A Review of Black Skin Research: Gloger Rule/Theory Dead or Alive?

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Introduction
The widespread dismissal of and indifference to the topic black skin embarrassingly run counter to the fundamentals of scholarly work. It is like saying, for example, that just because a cure/solution has been found in the course of biology history for cleft lips, cleft palates, epilepsy, tuberculosis, etc. any review/research of those and many similar topics of human life has been already closed and removed from scholarly work. As paleoanthropologists Smith and Wood (2017) reminded all researchers (of biology and skin color, including), "the overall [emphasis in original] research agenda of a discipline… must conform to science norms. This means, among other things, that… its knowledge is cumulative and progressive" (p. 672). One cannot improve that which is not researched/analyzed. What is most significant about black skin is that, as is obvious from the present review, just as misconceptions have been crafted and propelled about black skin by illustrious scholars, so too wrong attitudes toward and erroneous concepts about black skin continue to be perpetrated by eminent biology or science scholars and their outlets.
Gloger theory (1833) is an appealing theory, usually applied intentionally or unintentionally across biology and science fields. Fundamentally, Gloger theory takes the view that a cause-effect relationship exists between black(er) skin and warm(er) climate/region. To shed greater light on Gloger theory, a historical background of black skin has been laid out. If biology and in fact any scientific discipline aim to achieve a greater impact in the world, they ought to engage heads-on with the theories surrounding the concepts central to their work and to the world in which they operate, and black skin scholarship is no exception. As anthropologist Jablonski (2017) pertinently reminded skin color researchers, "the absence of scientific justification for races as 'biological real' does not mean that they are not socially real" (p. 7). To add to this dilemma, skin color represents one of the most conspicuous traits in the kingdom of living beings, from humans to animals to plants to microorganisms. Theories behind the "differences in biology brought about by racism" (Jablonski, 2020a, p. 6) cannot fail to warrant scrutiny. Oddly enough, black skin resides at the heart of racism and similar phenomena (i.e., slavery, poverty, unemployment, etc.). While racism, to name just this example, figures in human civilization as one of the deepest-seated evils, black skin is one of the least researched and most misunderstood topics of interest.
The diversity of the Black Jewish community is given much emphasis in the book of Lamentations when it reads, "her Nazarites were purer than snow, they were whiter than milk, they were more ruddy in body than rubies, their polishing [was] of sapphire" (Lamentations 4:7 Hebrew Interlinear Bible). Evidently, servants of God appeared to be cleaner and more shimmering (the actual translation or meaning of the Hebrew verb tzchu, used in text, Hebrew Interlinear Bible) than average people, with their bodies being ruddier than rubies and more polished or shinier than sapphires. Note that rubies display a strong blackish red whereas sapphires have a strong blackish blue or purple, all of which cannot be said of white skin. Of importance here is the phrase black like an oven, mentioned supra (Lamentations 5:10 Hebrew Interlinear Bible), that is also inapplicable to white skin. Some explanation is of the essence. By nature, smoke --especially when produced constantly as in the case of cooking --blackens metal or material so deep that it cannot (or can barely) be removed. In fact, a combination of smoke and burnt food items (e.g., oil, paste, soup, meat, bread, flour, etc.) occurring during cooking, causes a stove or oven to turn pitch-black, blackish red, or blackish grey. The insistence on and the superlative of black color in the stories of Job and Lamentations are a patent indication of black-skinned individuals. In addition, as is evident in the book of Lamentations, Black communities had a steady, distinct sense of their Jewish identity/nationality. The book of Lamentations states, "we have given the land [to] the Egyptians, [and to] the Assyrians, to be satisfied with bread" (Lamentations 5:6 Hebrew Interlinear Bible). More specifically, the book of Lamentations continues, "our inheritance is turned to strangers, our houses to aliens" (Lamentations 5:2 Hebrew Interlinear Bible). Both the story of Job and that of Lamentations, reflecting the Near East world around the 6th century BC, allude to black skin and heat without any pejorative connotation. Furthermore, apart from Jewish and Egyptian nations, swarms of historical materials have demonstrated extensive presence of black-skinned communities aboriginal in much of Asia and in Siberia as far as the Caspian regions and Caucasian mountains (Herodotus, ca. 425 BC/1950, ca. 425 BC/1957, ca. 425 BC/1960Brook, 1999Brook, /2018Kolga, Tõnurist, Vaba, & Viikberg, 2013) without deprecation concerning black skin and heat. Black individuals were shown to be full members of the communities and regions in which they were living, something unusual for slaves or low-class individuals. For example, Herodotus (ca. 425 BC/1957) spoke of Ethiopians of Libya as having "of all men the woolliest hair" (7.70). Ethiopians of Libya could not be called so if they were not Libyan and the same holds true for Ethiopians of Asia, who would not have been identified so if they were not Asian (see below). Also Herodotus noted that among the Asian kingdoms that were bringing gifts to Darius, the king of Babylon, were also Colchians, whom he described as "dark-skinned and woolly-haired" (Herodotus, ca. 425 BC/1960, 2.104) and Ethiopians of Asia (Herodotus, ca. 425 BC/1950, 3. 92-94. 97). The description woolly-haired individuals indicates Black people.
Of paramount interest here is the fact that, according to Liddell andScott (1843/1996) celebrated Greek lexicon, the Greek word ούλότριχες (oulo-trikhes) employed by Herodotus (ca. 425 BC/1960, 2.104) when describing the Colchians, and translated by most commentators as woolly-haired comes from the Greek verb οὐλοτριχέω [oulotrikheo], meaning to have curly hair. A further note of interest is that regarding the Greek adjective that derives from the verb to have curly hair, namely, the adjective οὐλόθριξ, τριχος [oulothrikhs, oulothrikhos], which denotes someone with curled hair, Liddell andScott (1843/1996) unmistakably limited this notion to Blacks noting: "with crisp, curly hair, like negroes, opp. [as opposed to] εὐθύθριξ [euthuthris]". The adjective οὐλόθριξ [oulothrikhs] is composed of two particles: οὐλό [oulo] and θριξ [thrikhs], which respectively mean curly and hair. Here too, Liddell andScott (1843/1996) insisted and defined the adjective οὐλός [oulos] as: "of the crisp, woolly hair of the negro". As can be seen, the adjective οὐλό-θριξ is being opposed to the adjective εὐθύθριξ [euthuthrikhs], which stands for straight-haired. Furthermore, Herodotus (ca. 425 BC/1957, 7.70) was able to distinguish the Ethiopians of Egypt with straight hair and those of Libya with the curliest hair of humans. Without question, the Colchians were nothing but Black with curled hair. Curled or coiled hair is a characteristic notably employed by torrid zone theory to underscore the intense heat of Africa, as Smith (1787Smith ( /1810 declared below that just like wool and vegetable leaves, hair curls itself up when put close to a flame. In addition, slaves much less foreign black-skinned individuals --if and only if slaves had been imported to the area as some authors tend to argue (Blakely, 1986) --could not have been allowed to form and have kingdoms in the host land, with the ability to own and ship precious gifts via official delegations to the reigning king (Darius) on behalf of their own kingdoms. Another example, Brook (1999Brook ( /2018 enumerated several communities of Black individuals living in Siberia, Russia, until the 1880s and later, such as "Black Khazars" (p. 4), "the Magyars [or] the Black Ugry" (p. 5), and "Kuban Bulgars (Black Bulgars)" (p. 125). Not a small number of facts clearly certify a presence of black-skinned people in this part of the world. "For instance, the seventeenth century Arab traveller Ezliya Chlebi encountered black Crimean potters" (Blakely, 1986, p. 11). Slaves are usually kept deprived from basic services/liberties and unmingled with local populations. However, in addition to being able to form a kingdom and send gifts to Darius, Black communities in the Caucasian mountains were so intermingled with local communities that Russian travelers were astounded and contrasted them with Blacks in the US (Blakely, 1986). One characteristic of slaves is that slaves usually have their masters known, and well-identified because slaves' masters intervene and speak on behalf of slaves, especially when dealing with foreigners or visitors. The geographical conditions of Siberian regions did not allow constant and easy access of foreigners or researchers. The indisputable aboriginal existence of Black Caucasians completely belies all claims of Black slaves or Black aliens in the Caucasian region or other regions beyond the equator.
Thus, "it was not until early in the twentieth century that the Russian public was made aware of the existence of settlements of several hundred Negroes in the Black Sea region" (Blakely, 1986, p. 6). The thesis of slave trade as an explanation of black-skinned communities in ancient world is untenable in many respects. The likeliest reason might be that there was no large-scale labor that would require a titanic, perilous, across-continents, and long-distance trade of hundreds or thousands of foreign-born black individuals in a given land of the Old World, wherein man power was otherwise locally available for merchant, royal, and domestic chores. Another likeliest reason is that private or royal palaces would not and usually do not require long-distance and large-scale shipping trade of foreign or black populations because palaces have no room/space to house and attend to such big personnel made of children, women, and men of all kinds. Normally, it can be argued that kings and emperors might want to ship (via the military) one or two Black or foreign concubines for romantic purposes, or one or two strong Black or foreign men for heavy-duties domestic chores, and not large-scale communities in the slightest. Also, such a costly and challenging shipping business (of humans) would have to be profitable both for traders and buyers (Cibangu, 2015), which is certainly not the case in this specific context of Asia and North Africa.
All in all, in the various communities and nations mentioned above from Egypt to the far east of the world, black skin was not denigrated nor associated with (some place of) heat. Most remarkable is the fact that, although on the one hand the concept others or foreigners could be the object of disparagement often described as barbaric (Gruen, 2011(Gruen, , 2020, and on the other hand the land of Kush, a foreign land, was noted for its wealth and militaristic power (Burrell, 2020), black skin was highly regarded throughout the ancient world. Equally, the concept heat was not stereotyped as exclusive to a given population or community, all of which is also observed earlier with king Akhenaten narrative in the 14th century BC (Foster, 2001). The predominance of aboriginal black-skinned individuals in the Old World from North Africa to the far east of Asia renders less likely both the thesis of slave trade of Blacks and that of deprecation against black skin. What's more, the persistent designation, during pharaonic times, of Egypt as Khemet, meaning Black nation alongside a steady awareness of skin color as distinctive of nations (Foster, 2001) would have constituted a serious threat to the sovereignty, famous wealth, and diverse landscape of ancient Egypt if Blacks had nothing to do with the black land. Most curiously, the words Kush or Cush (now Sudan) and Egypt relate to the same Hebrew radical ‫שּׁוּכ‬ [kush] (Brown, 2001), meaning black. Even most worthy of note here is that the Hebrew word Kush, black skin, was readily indisputably applied to persons in Israel, Assyria (now Syria), Egypt, Arabia, Ethiopia, South Sudan, etc. No White nation governed by White kings or rulers would allow their land to be called black land for three millennia.
In Antiquity, black skin was normally associated with Ethiopia, a millennia-long Black nation of unbeaten and stand-alone civilization, with its own writing, language, and political system. As is now clear, black skin was not the subject of deprecation for three millennia BC and for much of the first millennium AC roughly after the turn of the 17th century. In the first half of the 1700s, Swedish naturalist Carl Linnaeus (1707Linnaeus ( -1778 introduced the first classification of human species based on skin color and latitude, distinguishing: red (i.e., Americans), yellow (i.e., Asians), white (i.e., Europeans), and black (i.e., Africans) species (Burrell, 2020). The classification --created by Linnaeus in the first volume of the 10th edition of his book Systema Naturae, in 1758, first published in 1735 --carried an explicitly disparaging description of Africans as being lazy and negligent species or varieties (Linnaeus, 1735(Linnaeus, /1758. Skin color was ever since characterized as synonymous with and as a measurement for the standards of decency and civility, with Blacks [niger] being at the lowest level, and Whites [albus] at the highest one. Proper to Linnaeus system, or Linnean system as it is also commonly called, is the notion gradient or hierarchy of species based on geography or latitude for skin color and for human behavior. Black skin thus became a species, namely the Africanus, niger [African, black] species, and its characteristics as well as the descriptions or assumptions made on them were (believed to be) congenital. The Linnean skin color-based classification of humans drawn along the lines of the four continents (i.e., America, Europe, Asia, and Africa) will have an unspeakably immense impact in academia and the general public in the 18th-19th century and onward. The inferiority of black-skinned peoples and their skin was thus put forth. On the heels of the Linnean classification of human varieties/species, German philosopher Immanuel Kant (1724Kant ( -1804, started teaching summer courses on physical geography in 1756 at the University of Königsberg [now Kaliningrad, Russia], the last of which he published in 1775 (Kant, 1775)  Black skin came to be defined as black race and white skin as the icon of whiteness. With Kant popular summer teachings on physical geography delivered for nearly two decades, from 1756 to 1775, the idea of black skin as substandard, black race and whiteness as a model of humanity will be lastingly etched in the minds of people in Europe and beyond. Climate was presented as the reason for the color of black skin (see Kant, 1775, p. 8). Deprecation against black skin climaxed in particular in the first half of the 1800s with the advent of articulate torrid zone theory along with a rapid rise of transatlantic slave trade. The rise of transatlantic slave trade was expedited by new technologies invented during the Industrial Revolution (e.g., steam engine, electricity, telegraph, etc.). As can be imagined, the shift and prediction from biology (i.e., skin color) to social values/standards (i.e., decency or civility) has proven to be the toughest nemesis of skin color research in particular and biology or academia in general. A review paper such as the present paper reappraising Gloger theory and its background is definitely in order.

From the 18th Century Onward
Deprecation against black skin might be hearkened back to the application of what might be called torrid zone theory, a theory whose ingredients were arguably first laid out in 1646 in Paris by prince Armand de Bourbon (1629-1666) --prince of Conty, second son of Henry II, also called prince of Condé (Bourbon, 1646). In a reflection about the nature and manifestations of the sun, Bourbon (1646)  [And yet the torrid zone of the earth is a place, wherein most things are flammable, energy is flaming, or converting into heat. Therefore, the torrid zone of the earth is a place in which more heat rises in abundance… And yet the torrid zone of the earth is a place where most water is mixed with the air and emissions of the earth, which is salty and mostly dirt that is even being roasted by the fire of the sun or even being mixed with water. Therefore, the torrid zone of the earth is a place where most matter is flammable]. (pp. 29-30) As can be realized, torrid zone theory is derived from the Latin phrase torrida zona, taken from Bourbon (1646) work seen above, simply transliterated in English as torrid zone. However, in 1810, more than a decade after the defense of Blumenbach doctoral thesis, torrid zone theory received a clearer exposé with American Presbyterian minister --and the seventh President of Princeton University, USA, from 1795 to 1812 --Samuel Stanhope Smith (Kelly& Jamoussi, 2016;Mann, 2009;Noll, 1989;Thornton, 2020) in his 2nd-edition (Smith, 1787(Smith, /1810 book (details below). Blumenbach described extensively the effects of climate on human body, but he was of the opinion that under the effect of African burning heat black skin came from bile (see Blumenbach, 1775Blumenbach, /1795. This is probably the reason why in his work Gloger (1833) did not refer to Blumenbach (1775Blumenbach ( /1795. Nonetheless, in his description of Africa, Blumenbach (1775/1795) put forth torrid zone theory. In a nutshell, torrid zone theory holds that scorching, extreme temperatures are unique to and worst in Africa, and thus, are what caused Africans' skin to be black and Africans' hair to be curled. Concerning black skin, torrid zone theory has left an indelible impression on European and North American audiences.
Central to torrid zone theory is the notion "Varietas caucasia [Caucasian variety]" (Blumenbach, 1775(Blumenbach, /1795, first introduced in the classification of humans by Blumenbach in 1795 in his 3rd-edition book as the only race (i.e., Whites) encapsulating beauty as well as human origin and rationality. The concept Caucasian was analyzed also by Freedman (1984) and Holubar (1996), among others. Blumenbach classification of humans was modeled on the Linnean classification (Linnaeus, 1735(Linnaeus, /1756) and on the Kantian classification (Kant, 1775). The Linnean classification was used primarily for its concept species and/or varieties whereas to a greater degree the Kantian classification provided the concept whiteness. The reason given by Blumenbach (1775Blumenbach ( /1795 in using the classification Caucasian was taken from an account of the 18th-century French explorer Chardin (1771) who claimed to have been impressed by the beauty of the women he encountered in the Georgian/Caucasian part of Siberia. Chardin (1771) indicated, Le sang de Georgie est le plus beau de l'Orient, et je puis dire du monde… La Nature y a répandu sur la plupart des femmes des graces qu'on ne voit point ailleurs. Je tiens pour impossible, de les regarder sans les aimer. L'on ne peut peindre de plus charmans visages, ni de plus belles tailles, que celles des Georgiennes [The blood of Georgia is the most beautiful of the East, and I would say of the world… Nature has provided most women with graces not seen elsewhere. I find it impossible to love those women when I watch them. One cannot describe faces more charming and heights more beautiful than those of Georgian women]. (p. 123) It needs to be underlined here that the above statement does not amount to a valid and representative description of Siberia, a region vastly researched by Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a and Gloger (1833), who both characterized Siberia as a region of marked diversity (details below). It might also need to be said that the romantic description of Chardin (1771) is not entirely different from the one offered by Stanley (1878) about the women he found in Uganda. Stanley (1878) wrote, For pure Waganda are not black by any means. The women and chiefs of Mtesa who may furnish the best specimen of Waganda, are nearly all of a bronze or a dark reddish brown, with peculiar smooth, soft skins, rendered still more tender and velvety to the touch by their habit of shampooing with butter. Some of the women, I observed, were of a very light red-gold colour, while one or two verged on white. [emphasis added]. (pp. 196-197) Based on the aforesaid reasoning and description of Blumenbach (1775Blumenbach ( /1795 referring to Chardin (1771) portrayal of the notion Georgian/Caucasian, the classification and qualification of Caucasian perfectly fit in with Waganda women. The point noted above by Stanley worth-making here is the aboriginal presence of white-skinned individuals in Uganda on the equator. Yet, the word Caucasian is an old term utilized to designate nothing but the Caucasus mountains or Caucasia mountains. For example, Herodotus (ca. 425 BC/1950, 3.97) used the word Caucasian in the 5th century BC. The Caucasus mountains are located between Black Sea and Caspian Sea in Eastern Europe. With torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 (1736/1778, p. 69). This means that Whites could not share the same origin or dignity with Blacks. Thus, Feijóo (1736/1778) concluded, "el color negro de los Etí opes es de tal modo natural, y congé nito a aquella raza de hombres, que por ningún accidente puede alterarse, ni en ellos, ni en sus sucesores [the black color of Ethiopians is so natural and innate to this race of humans that it cannot be changed by any means in themselves or their descendants]" (p. 68). Most clearly, in the 19th century, the idea of inferiority particularly assigned to Black populations gained greater traction with Swiss-born American naturalist Jean Louis Rodolphe Agassiz (1807Agassiz ( -1873, who earned a PhD in natural philosophy at the University of Erlangen (Germany) in 1829 and in the following year 1830 a PhD in medicine at the University of Munich (Irmscher, 2013;Weissmann, 2013). Agassiz (1850) affirmed, race… and nevertheless there has never been a regulated society of black men developed on that continent, so particularly congenial to that race. (p. 143) The inferiority or the lack of civilized, regulated society of black-skinned individuals was claimed to be congenital to Africans, and thus appeared to have received an established and entrenched dimension in university circles. Agassiz was described to be "the incorrigible racist" (Irmscher, 2013, p. 4), and for the same reason "a leader of the anti-Darwin crusade" (Weissmann, 2013(Weissmann, , p. 1289). Agassiz lectured for more than two decades at Harvard University and Cornell University, which lent prominence to his teachings. Such a condition has dwarfed the research environment of black skin and of related individuals and communities.
Similarly, although Smith (1787Smith ( /1810 believed in and defended the unity of mankind, he vigorously advocated the superiority of white skin as the beacon of civilization. To a great degree, transatlantic slave trade since the 15th and 16th centuries came to provide additional, solid grounds for deprecation against black skin in Europe and North America (Kendi, 2017;Sussman, 2014), with Blacks not being seen as humans and being denied aboriginal existence beyond Sub-Saharan Africa (details below). A further boost for deprecation against black skin was with the concept dark continent introduced by British-born American journalist and explorer Henry Morton Stanley (1841Stanley ( -1904, noted above, during his travels to Africa (Stanley 1878(Stanley , 1899. As Stanley (1878) diarized one of his expeditions, upon nearing the African continent, "A wave of my hand, and the anchors were hove up… The sun sinks fast to the western horizon… as we glide away through the dying lights towards the Dark Continent" (p. 69). Perhaps to make things even worse, from the 20th century onward, with the dissemination of skin-bleaching creams, cosmetic global companies have nothing but intensified deprecation against black skin (Dixon & Telles, 2017;Hall, 2018Hall, , 2019. For better or worse, Gloger theory can be used to that effect.

Significance of the Study
The significance of the present review dovetails well with the salience of black skin. Indeed, in an increasingly interacted, instantaneously informed, and racially intermingled world, the topic black skin, how it is viewed and what is done to it, has been rising to the fore. Meanwhile, the history of black skin and/or black-skinned people is abuzz with examples of bad, unscientific theories leading to bad decisions and to a fractured world (Jablonski, 2021a;Kendi, 2017;Samson, 2013;Sussman, 2014). Thus, critically reassessing Gloger theory in light of its historical/social roots has the potential to allow for a better understanding of black skin and smoother integration of black-skinned individuals. Such an understanding will in turn pave the way for a more constructive conversation on and informed deterrent to racial inequality and injustices seen to be relentlessly wreaking havoc on our growingly multiracial world.

Clarification
One major concept needing to be clarified from the outset is that of theory. Many a good material of life sciences and social sciences has used the phrase Gloger rule (Glaubrecht & Haffer, 2010;Delhey, 2017Delhey, , 2018Delhey, , 2019, some authors have referred to the term Gloger school (Homeyer, 1868). This paper preferred the phrase theory, providing more freedom or room to the researcher and the researched than a rule does. Thus, "theory is a set of propositions that explain specific relationships between the phenomena being studied" (Cibangu, 2012, p. 98). As researchers, theory is a core component of our inquiries and our interactions with the world in which we live. Theory represents a series of statements used as a blueprint to investigate and/or interpret a research question. One term variedly employed in place of theory is hypothesis (Beck, 2019;Delhey, 2017Delhey, , 2019Elias & Williams, 2015Jablonski, 2017Jablonski, , 2018Jablonski & Chaplin, 2017;, which also tends to give more leeway to the researcher and the researched. As can be seen, in academic circles, freedom of the researcher and indeed of the researched is key to the impact made on the world -especially when the researched are human. Sure enough, animals, plants, and nature in general are increasingly believed to be endowed with inalienable rights more than ever before, in the hopes of bringing about healthier, safer, or more sustainable ecosystems. All in all, Gloger theory or hypothesis comprises a set of Gloger statements or propositions taken to interpret a given biological phenomenon or topic. Along with a conclusion, the rest of the paper is structured around four sections: (1) background of Gloger theory, (2) key arguments of Gloger theory, (3) discussion, and (4) pathways of future research on skin color.

Background of Gloger Theory
In this section, attention is given to a brief biography of Gloger and to key figures that have shaped or contributed to Gloger theory. Constantin Wilhelm Lambert Gloger was born in Kasischka (then southeast of Germany) on September 17, 1803 and died in Berlin on December 30, 1863. Gloger grew up in Upper Silesia, at the border of Poland and Czech Republic. After his high school (or secondary school) studies in Neiße (Nysa, Poland), he took zoology at the University of Breslau, now Wroclaw (Poland) where he earned his PhD in the same field in July 1830 (Haffer, Hudde, & Hillcoat, 2014;Glaubrecht & Haffer, 2010). He did much of his work particularly on birds of the Eurasian region. After earning his PhD, he taught natural history at the Gymnasium (High School) of Breslau until 1842, at which point he moved to Berlin to undertake as an independent researcher various bird projects nearly unsuccessfully. From 1853 till his death, Gloger was --for a modicum of stipend --a collaborator of German ornithologist Jean Cabanis, the editor of the Journal für Ornithologie [Journal of Ornithology] and director of the Berlin Museum. Part of his work helping Jean Cabanis, Gloger published quite profusely in the Journal of Ornithology (Haffer, Hudde, & Hillcoat, 2014). As Gloger was undertaking his work, three individuals came to be key figures with invaluable impact on his arguments and writings.
The first individual who had influenced Gloger was University of Berlin (now Humboldt University) German zoology professor Martin Heinrich Karl Lichtenstein (1780-1857, founder of the Zoological Museum of Berlin (Haffer, Hudde, & Hillcoat, 2014;Glaubrecht & Haffer, 2010). Indeed, during his studies at the University of Breslau (Poland), Gloger enrolled in courses of winter semester at the University of Berlin in the academic year 1824/1825, over the eight-month period of which he was exposed to the teachings of professor Lichtenstein --the then director of Berlin Natural History Museum --mentioning the phenomenon of bird coloration presumably driven by climate (Haffer, Hudde, & Hillcoat, 2014;Glaubrecht & Haffer, 2010). On this note, Haffer, Hudde, and Hillcoat (2014) wrote that Lichtenstein himself published hardly anything on these important conformities, but was in full agreement with his student Gloger using the Berlin [Natural History Museum] material to study geographical variation in the coloration of birds and mammals and later publishing his findings in a long paper. (p. 71) Lichtenstein did not publish or cite a work on the topic of bird coloration, as is apparent from his foreword to Gloger work (Lichtenstein, 1833, pp. iii-iv). In the foreword to Gloger work, Lichtenstein is seen to be more thrilled by Gloger brilliancy and enthusiasm for research than by the topic of geographic colorations.
The second key figure that had shaped Gloger theory after Lichtenstein was German naturalist and explorer of Siberia and Far East, Peter Simon Pallas (1741-1811) who completed varying extensive research on animals of the Eurasian region (Pallas, 1780a(Pallas, , b, 1784(Pallas, , 1811(Pallas, /1831a. As Haffer, Hudde, and Hillcoat (2014) clarified, before Lichtenstein, "this phenomenon [of bird coloration] had already been pointed out by… Pallas" (p. 71). More clearly, Gloger received the idea of climate-led coloration of birds from Pallas published work entitled Zoographia Rosso-Asiatica (Pallas, 1811(Pallas, /1831a). This work is referred to by Gloger (1833, pp. v-vi). In his book, Gloger (1833) cited Pallas research substantially. Concerning bird coloration, Pallas (1811/1831a) noted, Semper enim aves ad ea loca, ubi exclusae sunt, ad prolificandum revertuntur, ideoque climatis effectu perplures generationes continuato, etiam colores mutare possunt, ut exemplo in Alauda nivali demonstravi [Indeed, birds can change even colors and therefore shall continue to reproduce under the effect of climate through many generations in those places where they were excluded and are returning to proliferate, as I demonstrated with an example of Alauda nivali (skylarks)]. (p. 185) Part of the above statement on coloration is cited on the frontpage of Gloger (1833) book. The idea of coloration was reflected upon by Pallas (1780a, pp. 234-235). Bird coloration was demonstrated to be a function of climate effect in a research run by Pallas on skylarks species in the Eurasian region.
What is most notable with Pallas research is that black coloration is predominant across the artic region as well as across the body parts of birds and animals species (Pallas 1780a(Pallas , b, 1784(Pallas , 1811(Pallas /1831a. As a result, black coloration is not a latitudinal manifestation, but rather an internal mechanism of birds to adapt to ambient temperature. Meriting special consideration here, however, is that Pallas research about climate-based coloration of animals in the Eurasian region was arguably first published in 1780 (Pallas 1780a, b, details below) the year in which Lichtenstein was born (Haffer, Hudde, & Hillcoat, 2014).
The idea of climate effect on species or life goes back to immemorial times with the effect of the weather on plants. In this respect, Pallas (1780b) was of the belief that climate effects do not necessarily engender a variation by species or by latitude. In his paper on the variation of animals, Pallas (1780b)  Identical latitude, diet, longitude, and climate are indicated to be characteristics of people with entirely different traits and skin color and hair. The variety of color, skin, and hair shown in peoples living across the Siberian region, as demonstrated by various authors such as Pallas (1780b, pp. 80-81), Herodotus (ca. 425 BC/1950, 3. 92-94. 97), Brook (1999Brook ( /2018, and Kolga, Tõnurist, Vaba, and Viikberg (2013, p. 88), comes in striking contradiction with the notion Caucasian race propelled by torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 as the sole autochthone people of the Caucasian mountains. The contradiction is further compounded by the predominance of lighter-complexioned skins observed in equatorial Africa by Stanley (1878Stanley ( , 1899, a first-hand researcher of that region, not counting the existence of aboriginal un-mixed Black communities in Siberia (Brook, 1999(Brook, /2018Herodotus, ca. 425 BC/1950, 3. 92-94. 97) mentioned earlier. The variety of humans in the Siberian region has led Blakely (1986) to consider "this general area… richer in mystery and fable than any other in the world" (p. 5). This broad-based and proven variety is key in Gloger arguments. For example, Pallas (1780b)  s assume even the effect of a climate foreign to an animal, and more powerful than it really is, we still can never make sense of the fact that plenty of species that live in two continents and that have spread from the freezing zone to the tropics, have not varied and have not continually changed their form and their nature… Even man who has become indigenous to all climates and regions of the globe has kept his species pure and has undergone no more than superficial changes of skin and hair]. (p. 80) The point is that climate effects cut across species and latitudinal boundaries, and thus cannot be categorized as per species or latitude. Pallas argument of climate effects is an indispensable element to Gloger arguments. Indeed, Pallas position about climate effects is a complete reversal of torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. Moreover, although Pallas (1811/1831a) was an ornithologist, he made a remark of utmost significance for the African continent and the species thereof --even as torrid zone theory was brewing the widest during that period of time in the late 1700s and early 1800s when he undertook much of his research (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. Statements made about the African continent ought to be open to future research, as opposed to being stereotyped regardless of whether they are proven or not. Pallas (1811/1831a) affirmed, Et videtur sane pluribus constare speciebus, quam quae hactenus sunt notae; ex Africa enim semper aliquid novi expectandum, donec interiora hujus vastae continentis innotuerint [Also the plurality of species in Africa appears by all means to be self-evident, and there are many more than those observed so far, because from Africa indeed there is always something new expected until the interior variables/aspects of this vast continent become fully known]. (p. 180) Reconsideration of all too often taken-for-granted assumptions about Africa is immeasurably essential to a better, safer theory of black skin and the populations thereof. Torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787/1810) did not do a good job regarding biogeographical research on the African continent. The third and last key figure after Pallas and perhaps the most influential figure ever to have affected Gloger theory was German naturalist and explorer Alexander von Humboldt (1769Humboldt ( -1859, who invented some of the first tools for measuring temperatures and latitudes (Norder, 2019;Pausas & Bond, 2018;Rupke, 2021;Wulf, 2016), and whose thoughts are abundantly cited by Gloger (Gloger, 1833, pp. 13-15, pp. 33-34, pp. 61-62, pp. 106-107). Humboldt is known for the theory that organic life tends to increase and multiply as one moves nearer the tropics. This theory is commonly designated latitudinal gradient in species diversity (Beck, 2019;Fieldsend, 2020;Hanly, Mittelbach, & Schemske, 2017;D. Jablonski et al., 2017; or latitudinal gradient (Bartels et al., 2020;Kerkhoff, Moriarty, & Weiser, 2014). It is crucial to emphasize that Humboldt spoke of organic life or bio-diversity in general, without any limitation to or predilection for a specific location or ethnicity. As Humboldt (1808) indicated,

Je näher dagegen den Tropen, desto mehr nimmt Mannigfaltigkeit der Bildungen, Anmuth der Form und des Farbengemisches, ewige Jugend und Kraft des organischen Lebens zu.
[The closer one moves to the tropics, the more there is an increase in the multiplicity of growth, the beauty of design, and the mixture of colors as well as the continual bloom and vitality of organic life]. (pp. 167-168) As noted above, the colorfulness, fluidity, growth, vitality, and bloom of biodiversity increase with latitude. It needs to be borne in mind that abundance of life is spread across the globe.
Ist aber auch Fülle des Lebens überall verbreitet; ist der Organismus auch unablässig bemüht, die durch den Tod entfesselten Elemente zu neuen Gestalten zu verbinden: so ist diese Lebensfülle und ihre Erneuerung doch nach Verschiedenheit der Himmelsstriche verschieden [But the abundance of life is also spread all over (the earth); and organism endeavors relentlessly to fasten the components released by death, together into new forms. Then this abundance of life and its renewal, however, vary according to the differences of hemispheres]. (Humboldt, 1808, pp. 166-167) Death or the apparent interruption of productivity is presented as a way in which nature firms up life components. Interruption of life is not the same as absence of life, rather it's an affirmation of life. This is, as Humboldt (1808) explained, "denn Flüssigkeit ist Bedingniss zum Leben [because fluidity is a prerequisite for life]" (p. 167). Life cannot be restricted to a concept, form, variable, or process. As claimed earlier, the idea of life found across the globe was also propounded by king Akhenaten in ancient Egypt over three millennia ago (Foster, 2001). Perhaps most central to Gloger background is the idea developed by Humboldt (1831, pp. 407-409) and followed considerably by Gloger that, due to an array of variables, latitudinal distance is not a straightforward, mathematical line.
This idea is given more prominence with the fact often forgotten that the division between northern hemisphere and southern hemisphere starts at the equator. What this means is that northern hemisphere encompasses all the equatorial section north of the equator and the pole to the north just as southern hemisphere comprises the entire equatorial section south of the equator and the pole to the south (La Condamine, 1745). Indeed, French naturalists and geographers, namely La Condamine (1745) and his companions, undertook some of the first geodesic measurements on the equator and left a monument in Ciudad Mitad del Mundo [Middle of the World City] in Quito, Ecuador (see Table 1), showing the northern hemisphere on one side and southern hemisphere on the other. At this monument one can stand with one foot in the northern hemisphere and the other in southern hemisphere. One more specific reason for Humboldt (1808, 1831) insistence on latitudinal variation along with the universality of life, ensuing fluidity, and heat can be found with Blumenbach (1775/1795) torrid zone theory. While La Condamine (1745) and Humboldt (1808Humboldt ( , 1831 made seminal measurements and observations of the equator and latitudinal differences, they never defined the concepts heat, radiation, or sunshine as limited to a specific location/weather much less Sub-Saharan Africa. Because the earth is (viewed as) a sphere, the notion equator was thus understood as the dividing line at which geomagnetic force increases the most as one moves from the tropics toward that line (Korte & Mandea, 2019). No skin color was implied or predicted.
As indicated earlier, while torrid zone theory was first put forth by Blumenbach in 1775 in his doctoral dissertation at the University of Göttingen, it was fully fleshed out by Smith (1787/1810). Smith stated, "in various districts of the torrid zone of Africa, many of their domestic animals, and particularly their dogs, and common poultry, as well as the human inhabitants, are uniformly black" (1787/1810, p. 78). To show the fiery effects of the torrid zone in Africa, Smith (1787/1810) recounted, Modern travellers, who have explored the interior of that continent [Africa] with the greatest intelligence and care, inform us that, although … there are shady forests and a fertile soil, yet almost the whole region embraced between the tropics is a tract of sand that often literally burns. This state, not of the atmosphere only, but especially of the earth… will have its effects in increasing the close nap of the wool, for the same reason that a hair held near a flame will coil itself up, or the leaves of vegetables be rolled together under the direct rays of an intense sun… The hair as well as the whole constitution, suffers, in that region the effects of an intense fire. (pp. 96-97) Burning sand as well as the atmosphere of torrid zone are presented to be the cause of Africans' black curled hair and black-burnt skin. To emphasize, Smith (1787/1810) posited that "something may be ascribed also to the excessive ardor of that region of burning sand. Africa is the hottest country on the globe [emphasis added]" (pp. 95-96). Knowledge of torrid zone theory is foundational to a crisper picture of Gloger theory in particular and of skin color literature in general. As Smith (1787/1810) put it, in the torrid zone of Africa, "all nature bears the marks of a powerful fire" (p. 221). All vegetation in this continent is said to be on fire. Principally, Smith (1787/1810) wrapped up his ideas, saying: "the whole interior [of Africa], as far as it has been explored, is represented to be a desert of burning sand which often rolls in waves before the winds" (p. 222). It is said that the winds on this continent are made of fiery waves, searing everything in their paths. Owing to such blazing climate conditions, a key tenet of torrid zone theory is the belief that human darker skin is located closer the equator and lighter skin is nearer the poles. As Smith (1787/1810) expounded, In tracing the various climates of the globe, advancing from the arctic circle to the equator, we find them marked with considerable regularity by the colour of the inhabitants. In the European continent, we meet, in the highest temperate latitudes, with a ruddy, and sanguine [pink] complexion, which is commonly conjoined with different shades of redness in the hair. We soon descend to a clearer mixture of red in white. And afterwards succeed the brown, the swarthy, and passing over into Africa, the tawny, increasing by darker and darker shades as we approach the hottest temperatures of the torrid zone. In the Asiatic continent we pass at once from the fair to the olive, and thence by various gradations in the darkness of the hue to the black colour which prevails in the southern provinces of the peninsulas of Arabia and India [emphasis added]. (pp. 35-36) As explained above, torrid zone theory presents a climate and latitude-based gradation of skin color. To be precise, Smith (1787/1810) was perhaps the most stalwart supporter of the idea of "general uniformity in the effect [of climate], as we proceed towards the North, or the South… that the various shades of complexion which distinguish the different latitudes are to be ascribed chiefly to the influence of climate" (p. 62). As is all clear now, torrid zone theory is a fairly attractive theory taken to be something of a mainstay for the characterizations of skin color among species (details below). Undoubtedly standing against torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810, especially its misconception on or regionalization of heat, Humboldt propounded the idea of heat as a universal feature of life, an idea that Gloger (1833, pp. 61-62) (Foster, 2001), who, in fact, in the 14th century ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; BC, presented the blast of summer as central to and indicative of life. In essence, the idea of universal heat along with that of life fluidity and richness is quite at variance with torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. As it becomes evident, the background of Gloger theory spans a vast and diverse arena: zoology, ecology, geography, ornithology, physics, biology, etc. The point that has the most bearing here is that the ideas and figures outlined above are essential to a better and firmer understanding of Gloger theory (details below).

Key Arguments of Gloger Theory
It is safe to state from the outset that Gloger theory has been profoundly influenced by Humboldt (1808Humboldt ( , 1831 and Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a. It bears stating also as is evident below that Gloger made considerable criticism against the major elements of his own teaching or research, in search of a firmer understanding of the topics at hand. Self-reflectivity is a crucial characteristic of Gloger arguments. Worthy of note here is the fact that the most known and popular version of Gloger theorycommonly called Gloger rule, as explained above --is the one articulated in 1929 by Bernhard Rensch the then curator of Berlin Natural History Museum (Rensch, 1929), in recognition of Gloger work done at Berlin Natural History Museum. As Delhey (2019) summarized, The term 'Gloger's rule' was coined by B. Rensch in 1929 and included different patterns of variation from those described by Gloger. Rensch defined the rule in two ways: a simple version stating that endothermic animals are predicted to be darker in warmer and humid areas due to the increased deposition of melanin pigments; and a complex version that includes the differential effects of humidity and temperature on both main types of melanin pigments -eu-and phaeo-melanin. The blackish eu-melanins are predicted to increase with humidity, and decrease only at extreme low temperatures, while the brown-yellowish phaeomelanins prevail in dry and warm regions and decrease rapidly with lower temperatures. (p. 129) The point made above was affirmed from different perspectives by Rensch (1929, p. 160) and Rensch (1936, p. 283). For accuracy sake, the Rensch-formulated theory of Gloger can be called Rensh-Gloger theory. While the Rensch-Gloger theory (Rensch, 1929) is exclusively focused on birds research, it associates animals pigmentation or melanization with climate changes via either a simple or a complex correlation. An informative review of Rensch-Gloger theory was done by Delhey (2019). All the same, the lack of clear mechanisms involved in the stated correlation of climate variation and animals color remains the nemesis of Rensch-Gloger theory. Speaking of Rensch-Gloger theory, Delhey (2019) alerted interested authors that "a complex rule that is not associated with a clear mechanism is a good candidate for confusion" (p. 1297). One reason might be that Rensch formulation of Gloger theory might have been an overstatement (or understatement?) of Gloger arguments. This has caused Delhey (2019) to draw the conclusion that "complex definitions combined with ambiguous use and only partial empirical support may be indicative that Gloger's rule should be declared invalid or, at least, reformulated" (p. 1307). As clarified above, this paper focused on Gloger arguments to reassess or (re)define Gloger theory. A full-fledged background was provided to allow for a broader and clearer picture of Gloger theory.
As noted supra, while Gloger expertise falls under the scope of ornithology, Gloger theory stretches far beyond the confines of avian research. This is evident already from the subtitle of Gloger (1833)  As shown in the statements above, the universal, all-encompassing rationale arising from Gloger teachings and/or arguments is very much in tune with the multidisciplinary nature of biology fields. More particularly, the universal rationale is consistent with Humboldt (1808, pp. 167-168) latitudinal gradient theory touched on earlier. This is the rationale in which Gloger theory here discussed is (to be) best situated.
Perhaps, Gloger theory is most firmly and clearly rendered in the following statement: Wenn es bekannt und gewiss ist, daß sogar die, schwarz gebornen, Neger zu bleichen fähig sind und besonders dann etwas heller werden, wenn sie noch jung bereits gegen Norden gebracht wurden; so darf man wohl billig wiederum gar nichts Wunderbares darin finden, wenn die frei lebenden Thiere durch abwechselndes Versetzen hier lichter, nach Umständen zum Theile weiß, und nach Süden hin dunkler wurden [When it is known and certain that even unmixed black-born individuals are able to bleach and specifically become somewhat lighter-skinned once they have been brought still young right to the North, then one should again so easily find nothing extraordinary when wild living animals would became brighter by moving to a different environment, partly white according to circumstances, and darker in the South]. (Gloger, 1833, p. 107) In somewhat another context, the same idea was loosely alluded to by Gloger (1833, pp. 14-15). While the explanation outlined above might sound grotesque, it best captures Gloger theory. More interestingly, when the subject black-born individuals is replaced by the concept Homo genus, Gloger theory makes total sense (details infra). Typically, as indicated earlier, Gloger received this impetus from Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a research. Gloger was to some degree convinced of his position because at that time, the 18th and 19th centuries, a number of authors (Albinus, 1737;Feijóo, 1736Feijóo, /1778Mitchell & Collison, 1744;Smith, 1787Smith, /1810) dismissed the effect of climate --at least directly --on the color of skin. It must be said in passing that Pallas (1780b) was even one of the most fervent detractors of climate effects (details infra). The point here however is that under the effect of climate, humans or living species bleach or darken, depending on whether the location is cold or hot. For more clarity, Gloger theory can be visualized using an equation as follows: W x L = C (W= Weather, cold or hot; L= Length: number of years, C= color of skin, white or black) Note that the equation/formula was certainly not devised by Gloger; it is employed here just for visualization purposes.
What the equation implies is that unmixed darker-skinned born individuals (Blacks) who had moved to northern regions (e.g., Europe or North America) would see their skin turn white after, say, 1 to 2 million years of being subjected to cold weather, the same is true for unmixed lighter-skinned born individuals (Whites) who had moved to tropical regions (e.g., Africa or South America), they will see their skin become entirely black after the same number of years. The number of years is not entirely known or determined in Gloger theory, but it is assumed to be long enough (at a younger age, for instance) in order to produce the desired effects of bleaching or darkening. More precisely, Gloger explanation can be best understood in light of torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810  In other words, it can be argued that by moving away from such a rather scorching zone, delineated in torrid zone theory earlier, it is only fitting to imagine that the skin of animals, humans, and even plants will not only cool off, but will also bleach whereas the hair or the leaves of plants will straighten up. Surely, Blumenbach (1775/1795) torrid zone theory, so well articulated by Smith (1787/1810) needs to be borne in mind for a better understanding of Gloger theory.
Although Gloger defined longer exposure of skin to the weather as a conduit for the bleaching or darkening of skin, he was one of the harshest skeptics of torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 the climate of these cities! Petersburg is located at a latitude of 5 degrees north of Kazan, and yet the climate of Petersburg is despite all the rigor much milder than that of Kazan]. (p. 53) The jarring differences in climate conditions shown above, about Russia, go a long way toward calling into question torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810). An array of variables are believed to account for these climate differences, such as sea level, wind, soil nature, distance to the sea, etc. (see Gloger, 1833, p. 5). Variations that inexorably crosscut latitudinal and geographical boundaries have been plentifully demonstrated across Siberia and beyond by numerous authors, for example, Humboldt (1831, pp. 399-400), Pallas (1780b, pp. 80-81), and Smith (1787Smith ( /1810, to name a few. Perhaps most particularly integral to this blatant variation is a preponderance of black color across Siberia and across an animal's body parts in this region of the world (Pallas, 1780a(Pallas, , b, 1784(Pallas, , 1811(Pallas, /1831a. The signal and widely proven variation crosscutting latitude, species, and animals body parts has left its marks on Gloger thinking. This will probably be the knell for Gloger theory, if not an impetus for a deeper look into the questions left open by Gloger. The variation shown in Siberian region, as amply validated by Pallas (1780b, pp. 80-81), proves the notion Caucasian race/variety to be nothing short of erroneous, unsubstantiated, and irrelevant. No wonder, Gloger (1833) did not use the expression Caucasian race/skin/variety at all, when talking about humans or Whites in his book, and yet he mentioned the Caucasus mountains more than once (p. 100, p. 146). This is despite the fact not only that Gloger (1833) was an expert of and familiar with the Siberian, Caucasian region, but that Blumenbach (1775/1795) classification with the just coined concept Caucasian race was famous at that time. Perhaps a more suggestive piece of evidence highlighting weather-and latitude-crossing variation is that no species/variety (i.e., birds or mammals) found in the Caucasian area (Gloger, 1833) has been named after the term Caucasian variety/species. This is one of the biggest contributions of Gloger arguments. Gloger did not name birds species by latitude or climate areas. This is also indisputable proof of the influence that Gloger received from Humboldt (1808Humboldt ( , 1831 and Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a, whose research did not identify species per latitude, weather, or body parts. There is no such a thing as a map discretely drawn along the lines of species, latitude, or climate conditions. Moreover, in all species, black color crosscuts latitude, weather, and body parts. Humboldt did not use the concept Caucasian although he was a student of Blumenbach at the University of Göttingen (Korte & Mandea, 2019;Wulf, 2016). Perhaps most importantly, despite the fact that Humboldt invented and used measurement instruments for latitudes and altitudes and that he was an avid traveler himself, he did not conceive or use a global map for the skin color of animals, plants, or humans. Pallas and Gloger did not design one, either, despite a real need for it in their research and that of others. Humboldt (1808, pp. 167-168) proposed the gradient of life diversity, but not of skin color by any means; nor did he insinuate such an idea despite his towering research on the properties and measurements of the equator. Thus, diversity of life on the equator means diversity of skin as well. The idea of savannah vs forest for the origin of early hominins contradicts the uniformity of skin toward the equator. The proof of variety is further verified by the evidence of aboriginal white-skinned individuals on the equator (see Stanley, 1878, pp. 426-427, details below). The thing with human species is that no human naked skin can be claimed to be safe in any location, weather, or latitude, without necessary added protections, especially for the infant, elderly, sick, and disabled, not to mention pregnant women and albinos. For example, because of variability (i.e., latitude, climate, species, etc.), however, the imaginary line from the equator to the poles --the centerpiece of torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 in accounting for black skin coloration or bleaching --is no longer as straightforward and predictable as claimed. Consequently, Gloger (1833) . (p. 59) As seen in the example cited earlier, the highest temperatures of North America are nowhere near as high as those of Africa. Using the notion equatorial zone, an important theme of torrid zone theory, Gloger (1833) maintained, "in der Äquatorialzone ist da selten Sonnenschein; Tag und Nacht sind gleich, das Wetter ist veränderlich [in the equatorial zone, sunshine is rare, day and night look alike, and the weather varies]" (p. 47). The hottest sunshine and its scorching effects, the hinge of torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810, are demonstrated to be lacking in equatorial Africa. The statement is also evidenced by Stanley experience in equatorial Africa when Stanley (1899) wrote, "on the 6th of November [1876] we drew near to the dreaded and black chill forest…and at last, bidding farewell to sunshine and brightness, entered it… We knew not whether it was a sunshiny day or a dull, foggy, gloomy day ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; [emphasis added]" (p. 101). With this statement Gloger (1833) distanced himself from torrid zone theory. This position fits in well with one of the most memorable warnings of Pallas (1811/1831a) seen earlier against the broad-brush statements of torrid zone theory made about the African continent. The prevalence of black-skinned aboriginal communities along with the diversity of skin color seen across North Africa and Asia as well as the stories of Job and Lamentations (Blakely, 1986;Brook, 1999Brook, /2018Herodotus, ca. 425 BC/1950, ca. 425 BC/1957, ca. 425 BC/1960Humboldt, 1808;Job 30:30 Hebrew Interlinear Bible;Pallas 1780aPallas , b, 1784Pallas , 1811Pallas /1831aLamentations 4:7-8, 5:10 Hebrew Interlinear Bible) is unmistakable testimony to latitude-crossing variety of humans. Humboldt (1808, pp. 73-74) spoke of black-skinned Tuaregs, among the natives of Libya, to which Gloger (1833, p. 60, see footnote (*)) referred.
As is now abundantly clear, variety in its manifold aspects comes to be a common thread running throughout Gloger arguments. Furthermore, because innumerable variables interfere with climate conditions at same or similar latitudes, Gloger (1833) intently held that "es… unmöglich bleibt, die Gränzen der klimatischen Varietäten streng geographisch zu bestimmen [strictly geographically speaking, it remains impossible to determine the demarcation lines of climate varieties]" (p. 30).
Weather variations are not the same as geographic variations or species, although they are mutually inclusive. This is a dramatic reversal of the notion varieties or species as expounded by the famous Linnean classification (Linnaeus, 1735(Linnaeus, /1758, followed by that of Kant (1775), and that of Blumenbach (1775/1795). The resulting challenge for researchers lies in how and where exactly to map out specific regions along with their skin colors, without confusing one with another. To illustrate, Gloger (1833) asserted, "Niemand aber auf irgend einem Punkte der Erde von einem (absoluten) Osten und Western reden könnte! [Nowhere on earth, however, can anyone speak of an absolute East and West]" (p. 30, see footnote (**)). This is more problematic with skin color, namely in figuring precisely how and where in a given region a skin color of the west differs from that of the east. More exactly, for example, hundred communities of Nubians (Foster, 2001) and Ethiopians of Libya (Herodotus, ca. 425 BC/1957) are residents of and aboriginal to large swathes of Africa outside of the equatorial, tropical zone. The same is true of hundred communities of Hottentots and Zulus, living at the same latitude, away from the equatorial zone. Yet, "the Hottentots seem to be a race by themselves" (Smith, 1787(Smith, /1810. With these and similar examples in mind, the challenge is how to differentiate a region's skin color from another, such as an equatorial African skin color from a non-equatorial one. Beside skin color itself, the concepts tropical, rainforest, and savannah regions are already highly subjective (Beck, 2019;Waide, 2019 (p. 110) Local geographic variations allow humans, birds, and animals to adjust their body temperature so as to become natural or endemic to the host location. The statement demonstrates an intrinsically built-in interaction between organisms and ambient system, a statement suggestive of Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a findings noted above. This means that "was man nicht begränzen kann, das soll man doch auch nicht trennen [what one cannot delimit, one should not separate either]!" (Gloger, 1833, p. 5). The argument points to the complexity of variability in the sense that while there is an irreversible interplay between environment and biology, one should not compare incomparable items nor separate inseparable items (details below in discussion section). In other words, Gloger (1833) Gloger (1833), climate effects unfold in such a way that what affects the environment (i.e., weather) should also affect biology (i.e., species). This is not saying that species and climate varieties are interchangeable, but that they overlap. While both Pallas (1780a, pp. 234-235) and Gloger (1833, p. 107) alleged that climate can produce effects on species, they demonstrated in light of sizable research that climate effects do not create species. The best illustration might be with rain and temperature. It is the case that rain and temperature affect a plant. But it is also the case that rain and temperature do not generate a new species of plant. Gloger argument on climate effects shown above is copiously supported by Pallas (1780b, pp. 78-80). The most challenging question is how to delimit the phenomena involved in the stated interplay between environment and biology. The question was left open, unsettled purposely by Gloger. To conclude this trail of thought, Gloger (1833)  Hiernach wird es nun in Bezug auf klimatische Varietäten zwar gewiß noch überhaupt recht viel zu untersuchen geben, und es werden der kommenden Zeit gewiß noch eine Menge von interessanten Thatsachen aufzufinden und festzustellen geblieben sein [Accordingly, there will still be of course quite a lot to investigate regarding exactly climate varieties, and in the coming years there will remain certainly a host of interesting facts to find and determine]. (p. 59) Because of the infinite variability of the phenomena and factors involved in the interplay between biology and environment, more specifically between black skin and ecosystem, it is of uttermost importance to be alert to newer insights and findings rather than being stuck to unproven ideas however appealing to a researcher's long-held beliefs these ideas can be. Much remains to be found and determined about skin color in general and black skin in particular.
In sum, Gloger (1833) argued that skin color is a function of a longer and earlier exposure of a person to a given climate, with warmer climate blackening and colder climate bleaching the skin respectively. As such, Gloger theory does not warrant support, but Gloger arguments about variability are stronger than his stated theory. Gloger (1833) theory appears to be a perfect replica of torrid zone theory propelled by Blumenbach (1775/1795) and Smith (1787/1810). Notwithstanding, Gloger (1833) highlighted the fact that an infinite number of variables significantly interfere with climate of areas located at the same latitude. To a great extent, this has invalidated the core argument of torrid zone theory, and by implication that of Gloger theory itself. For example, Gloger (1833) noted that species endemic to warmer climate have the propensity to become colder when they move to colder regions, and that species endemic to colder regions become warmer when settled in warmer regions. As a result, Gloger (1833) cautioned that climate variations are not in any way, shape, or form the same as species variations and that environment and biology are inextricably interconnected. Just as Gloger did not use the phrase Caucasian race/skin/variety despite its popularity at the time (Blumenbach, 1775(Blumenbach, /1795Kant, 1775;Linnaeus, 1735Linnaeus, /1758, he did not identify birds varieties by latitude or climate conditions. As explained earlier, no human naked skin is safe anywhere without additional protection; this is even more true for the infant, elderly, sick, disabled, women, and albinos (details below). The determination of skin color based on region is subjective, to say the least. In much the same way, Gloger (1833) discouraged authors from separating what they cannot delimit. In simpler terms, Gloger (1833) alerted authors that with regard to environment and biology quite a lot of things remain to be uncovered and identified.
Gloger theory and skin color scholarship in particular can be best assessed in terms of their relationship with or allegiance to torrid zone theory (Blumenbach, 1775]/1795; Smith, 1787/1810) on the one hand and to latitudinal gradient theory (Humboldt, 1808(Humboldt, , 1831 on the other. This is largely because torrid zone theory and latitudinal gradient theory have come to be the underpinning theories around and from which biology fields tackle black skin and similar topics. Authors of skin color, especially black skin, are not always aware and/or explicit about the underlying theories beneath their works. When drilled deeper, theories are an important tool to show the ways in which a research's specific mechanisms alongside units of analysis or variables have been (mis)used, (mis)understood, and (mis)applied. As seen above, antithetical to Blumenbach (1775/1795) torrid zone theory is Humboldt (1808) latitudinal gradient theory. Unlike the idea of the fieriest sand with the hottest temperature that destroy nature and all organisms, the idea of freshest, coolest, and richest life is the core of latitudinal gradient theory --as one moves nearer the equator. Ever since latitudinal gradient theory has been expounded in 1808, it has been investigated and proven unrelentingly across numerous disciplines.
This phenomenon [of latitudinal gradient theory] … is one of the most widely recognized patterns in biogeography. Scientists have argued for over a century about its understanding… Since then over 100 hypotheses have been proposed to explain increased biodiversity in the tropics but we still lack a satisfactory answer. (Beck, 2019, p. 673) Similar research was undertaken by Hanly, Mittelbach, and Schemske (2017, p. 1) as well as Fieldsend (2020, p. 271). Hypotheses, not mere beliefs, have yet to be formulated about torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. While more than a hundred theories have been suggested to authenticate Humboldt (1808) latitudinal gradient theory, no hypothesis or theory has been proposed to attest to the patterns, if any, of Blumenbach (1775/1795) torrid zone theory in Africa or elsewhere (details below).
Stated differently, despite its understandably powerful attraction, torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810) has yet to be thoroughly investigated, from the widely touted extreme, most intense temperatures to glowing sand to heat-curled vegetable leaves and people's hair to fire-scorched black skin, all of which believed to be unique to and rampant in Africa. Meanwhile the idea of burning sand, for example, (said to be) omnipresent throughout the African continent (Blumenbach, 1775(Blumenbach, /1795 clashes with the reality of not only life itself, but of savannah and forest and their biodiversity. The hottest or extreme temperatures will kill, irradiate, or, at least, reduce the richness of organic life, which is essential and proper to equatorial regions; the hotter is the heat the more species are destroyed. On this point, consider that Lake Baikal, located at 55.637N, is the largest by volume and the oldest (>27 million years) lake in ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; 2022 the world, yet it has just 52 species of fish, 37 of which are endemic. In comparison, Lake Victoria, located at 1.307S, is just 18, 000 years old, yet it has 566 species, of which 450 are endemic. (Schemske & Mittelbach, 2017, p. 600) As shown by its latitude, Lake Victoria is situated on the equator. The above finding was demonstrated by Stanley in equatorial Africa, in which he observed "innumerable varieties of plants which spring up with such marvellous rapidity" (Stanley, 1899, p. 102, the same idea was validated nearly a century earlier by Humboldt (1808, pp. 167-168) in equatorial regions of Latin America). Africa is not the hottest continent either. As Rafferty (2011) underlined, "although the climate supporting tropical rainforests is perpetually hot, temperatures never reach the high values regularly recorded in drier places to the north or south of the equatorial belt [emphasis added]" (p. 16). Interestingly enough, Gloger (1833) was one of the stiffest opponents of torrid zone theory, while at the same a defender of latitudinal gradient theory to the core. Although torrid zone theory lacked (and still does) empirical evidence since its inception with Blumenbach (1775/1795), it has become one of the most ingrained, defended, and believed theories of skin color research. The theory is without difficulty detected in countless modern-day skin color materials.

Discussion
Torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810) has been the underlying theory according to or against which the discussion of materials related to black skin or skin color scholarship has unfolded in the aftermath of Gloger theory. Torrid zone theory is also the top-tier theory of most skin color research. This discussion can be divided in two periods: the 19th century and the 20th century onward.

The 19th Century
One of the most critical and synoptic authors of the 19th century, researching black skin --oftentimes forgotten --is British naturalist Charles Robert Darwin (1809Darwin ( -1882, the founder of evolutionary theory (Briggs, 2008;Broecker & Moelling, 2019;Loxdale, 2010;Porter & Graham, 2016;Ruse, 2008). The research of evolution theory or natural selection enjoyed the participation of more than one eminent biologist. This is evidenced in a historical sketch presented by Darwin (1859Darwin ( /1873 in his 6th revised edition of the Origin of Species. One of those biologists was Alfred Russel Wallace (1823Wallace ( -1913 who was marked out to be a co-founder of evolution theory (Briggs, 2008;Caro, 2016;Costa, 2014;Loxdale, 2010). Although Wallace (1871Wallace ( , 1878 works/arguments gained popularity relatively a decade after Gloger death in 1863, they are consistent with and pertinent to Gloger (1833) research (details below). Taken to its basic form, evolutionary theory holds that biological life is a product of natural selection, wherein species struggle to survive in adapting to the challenges posed by the environment and/or the weather (Darwin, 1859(Darwin, /1873Wallace, 1871Wallace, , 1878. As seen below, evolutionary theory is indescribably widely espoused by skin color researchers. Even as Darwin and Wallace were the gurus of evolutionary theory, however, they were some of, if not, the most vehement and vocal opponents of evolution-based or climate-led explanation of black skin. On this note, it is helpful to bear in mind a notable reference made by Darwin (1871Darwin ( /1889 to Pallas (1780b). Equally, Darwin can be considered to be one of the staunchest detractors of torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 Of all the differences between the races of man, the colour of the skin is the most conspicuous and one of the best marked. It was formerly thought that differences of this kind could be accounted for by long exposure to different climates; but Pallas first shewed that this is not tenable, and he has since been followed by almost all anthropologists… This view has been rejected chiefly because the distribution of the variously coloured races, most of whom have long inhabited their present homes, does not coincide with corresponding differences of climate. (pp. 192-193) Conceptions of climate-derived skin color were found to be far-fetched in the 19th century. Darwin (1871/1889) continued, Whether the saving of the skin from being thus burnt is of sufficient importance to account for a dark tint having been gradually acquired by man through natural selection, I am unable to judge. If it be so, we should have to assume that the natives of tropical America have lived there for a much shorter time than the negroes in Africa, or the Papuans in the southern parts of the Malay Archipelago, just as the lighter-coloured Hindoos have resided in India for a shorter time than the darker aborigines of the central and southern parts of the peninsula… A very damp or a very dry atmosphere has been supposed to be more influential in modifying the colour of the skin than mere heat; but… D'Orbigny in South America, and Livingstone in Africa, arrived at diametrically opposite conclusions with respect to dampness and dryness. (p. 196) Natural selection proved to be impractical for and inapplicable to black skin or skin color itself. Using empirical research from around the world, Darwin (1871/1889) averred, If, however, we look to the races of man as distributed over the world, we must infer that their characteristic differences cannot be accounted for by the direct action of different conditions of life, even after exposure to them for an enormous period of time. The Esquimaux live exclusively on animal food; they are clothed in thick fur, and are exposed to intense cold and to prolonged darkness; yet they do not differ in any extreme degree from the inhabitants of Southern China, who live entirely on vegetable food, and are exposed almost naked to a hot, glaring climate… The Botocudos… as well as the other inhabitants of tropical America, are wholly different from the Negroes who inhabit the opposite shores of the Atlantic, are exposed to a nearly similar climate, and follow nearly the same habits of life. (p. 197) Even from the standpoint of life conditions, skin coloration is still unpredictable across the world's regions. These findings relay Gloger (1833)  The limitation of black skin to natural selection of the equator lacks common-sense context. To better make her point, Jablonski argued, Darwin's preference for sexual selection in matters of human variation blinded him to the importance of natural selection in producing the attributes of human skin… Human skin is functionally naked and as such served for hundreds of thousands of years as the sole interface between our bodies and the environment. (Jablonski & Chaplin, 2010a, p. 169, see also footnote 1; 2010b, p. 8962, see footnote *) The above defense does not validate by any means the idea that black skin is a product of natural selection. It is not true either that with his world-wide empirical research/data, Darwin presented black skin (and not white skin?) as a mere product of sexual, natural selection. Still, sexual selection does not justify in any way how/why/where black skin is an equatorial product. The criticism was made with even greater force by Wallace (1878) in the 19th century: "we have arrived at the conclusion that tropical light and heat can in no sense be considered the cause of colour" (pp. 219-220) of skin. It is important to notice how heat and light in the tropics are being excluded from the formation of black skin.
A complete, resounding invalidation of the argument portraying black skin as a product of natural, equatorial selection is with the watershed research done by the team of Australian geneticist Vanessa M. Hayes (Chan et al., 2019). This research locates the birthplace of Homo sapiens, not on the equator in Africa, but rather hundreds of miles away in the area around the formerly vast Lake Makgadikgadi, now a basin situated North-East of Botswana in the current Kalahari Desert, at the latitude of 25° south from the equator, at the border of the savannah region. The corrective attempt of using the word savannah vs forest (Jablonski, 2017) for the skin of early hominins renders heat something less of a factor in the claimed blackening process of skin, thus contradicting the gradient of skin toward the equator. The equator-directed gradient of human skin has been challenged by varying research. Gloger vehemently rejected the idea of heat associated with equator in Africa and with latitude. Also, research led by French paleoanthropologist Jean-Jacques Hublin (Hublin et al., 2017) has shown the birthplace of Homo sapiens to be located in Morocco, quite far beyond the equatorial/savannah region. Moreover, regardless of the skin color attributed to Homo sapiens, the discovery of human skulls excavated at the turn of the 1990s in Dmanisi, Georgia, east Asia, right in the midst of Caucasian mountains some 90 kms southeast of Tbilisi, the main city in the republic of Georgia, Asia, fully calls into question any attempt to explain black skin with the equator or latitude (Rightmire, Lordkipanidze, & Vekua, 2006). The Dmanisi skulls are overwhelmingly identical to the skulls of the Homo species unearthed in the Turkana basin of Kenya, Africa.
The equatorialization and slavization, by the lack of a right word, of black skin prove to be utterly unseemly. The equatorialization or slavization of black skin received greater, unexamined credence with torrid zone theory (Smith, 1787(Smith, /1810, especially with the summer teachings of Kant (1775) and the subsequent implementations of torrid zone theory by Jablonski (2017Jablonski ( , 2018Jablonski ( , 2021bJablonski & Chaplin, 2010a. The simple fact that thick foliage, the proper of a forest, is a barrier to light and moisture sharply conflicts with the argument of UVR peak exposure in equatorial Africa, not to mention that by virtue of latitudinal gradient of organic life as one moves closer to the equator, a savannah is made of tall, thick grass and bushes. The rampant idea that black-skinned peoples had not migrated to and/or lived in other continents up until the Europe-sponsored slave trade roughly in the 18th -19th centuries (Jablonski, 2012b) is untrue. This idea is rooted in torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 as well as in the Linnean classification (Linnaeus, 1735/1758) of human skin color and the Kantian doctrine (1775) of human races. The idea has led to an unconscionable practice of considering slavery as an identifier of black skin. Yet, aboriginal Black communities were scattered and lived across the Old World, as seen with massive ancient materials (Blakely, 1986;Brook, 1999Brook, /2018Brown, 2001 The equatorialization of black skin is further challenged by the recent thesis of multiple dispersals of Homo sapiens out of Africa (Lamb et al., 2018). Multiple dispersals presuppose multiple reasons other than UVR, meaning that when some Homo sapiens individuals had to leave the UVR-sweltering equatorial or savannah region, others did not see the point or feel the need to do so. In other words, the natural selection of UVR and hairlessness did not work for all Homo sapiens persons, not only on one but multiple occasions, in the same area of origin, equatorial, savannah region. And to top it all, the latitudinal uniformity of white human skin increasing toward the northern hemisphere as claimed by torrid zone theory deemphasizes or simply ignores the tremendous existence of Innuit and Siberian dark-skinned persons in arctic regions, the coldest places on earth. Arctic and freezing regions are being subsumed as part of white supremacy, with higher latitudes being presented as the innate province of white skin (Jablonski & Chaplin, 2010aJablonski, 2017Jablonski, , 2018Jablonski, , 2021b). Yet, diverse materials looked at above lavishly show the Caucasian or northern mountains to be a region of skin diversity since immemorial times.

From Ancient Times to 19th Century: Summary
From ancient times with the writing of the Egyptian king Akhenaten in the 14th century BC (Foster, 2001) to human skulls found in Dmanisi in the republic of Georgia in the Caucasian mountains identical to the skulls seen in Kenya (Rightmire, Lordkipanidze, & Vekua, 2006) to Herodotus (ca. 450BC/1950, ca. 450BC/1957, ca. 450BC/1960 in the 5th century BC to the Hebrew usage of the work Kush, black, across the Old World (Brown, 2001) to Black Jewish communities (Hebrew Interlinear Bible) to Black Caucasian communities (Blakely, 1986) in the late 19th century, black skin was held in high admiration, and was unrelated with the concept equator and the ensuing alleged human skin gradient.
Latitudinal gradient of life diversity put forth by Humboldt (1808Humboldt ( , 1831 presupposes diversity of skin on the equator. Systematic deprecation against black skin had not started up until Linnaeus (1735/1758) racialization of human species along with Kant (1775) teachings in the 18th century. Deprecation against black skin ballooned nearly uncontrollably with torrid zone theory (Blumenbach, 1775(Blumenbach, /1995Smith, 1787Smith, /1810. Dispelling popular, unchecked mischaracterizations of black skin, Gloger (1833) completely rebutted the notion heat associated with the equator as well as the notion latitudinal gradient of human skin.

The 20th Century Onward
The period of the 20th century onward has seen a position particularly conform to torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 as well as to Gloger (1833) theory. One of the best implementations of Gloger theory in modern day times, although Gloger is not explicitly stated in them, is with skin color researcher Jablonski (2009Jablonski ( , 2011Jablonski ( , 2012aJablonski ( , b, 2013aJablonski ( , 2017Jablonski ( , 2018Jablonski ( , 2021b. Jablonski presented one of the most coherent and influential contemporary accounts of black skin research (Jablonski, 2017(Jablonski, , 2018(Jablonski, , 2021bJablonski & Chaplin, 2010a. In light of Gloger theory and ensuing broad-based historical background perused in sections outlined above, a closer, deeper look at these accounts is needed for a better understanding of black skin and research thereof. The firmest arguments advanced by Jablonski on black skin hinge on three main ideas: (a) UVR [Ultra Violet Radiation; also called UV B-rays or UVB], (b) comparative evidence, and (c) high physical activity of Homo genus.
These prolifically endorsed statements of Jablonski attach full weight to torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. To demonstrate the intensity of UVR in equatorial/tropical Africa Jablonski referred to NASA map (Jablonski, 2009(Jablonski, , 02:59-03:03, 2011 as well as to two figures made from an interpretation of NASA data (Jablonski & Chaplin, 2010a, pp. 175-176;2010b, pp. 8964-8965). Consequently, Jablonski (2017) made clear, saying: "at the equator and within the tropics, average UVB is high… Outside of the tropics, average UVR are much lower" (p. 4). This theory is called "the geographical gradient of human skin color" (Jablonski, 2017, p. 6). The theory is inherited from the Linnean classification (Linnaeus, 1735(Linnaeus, /1758) of human skin color encountered earlier. It follows from the reasoning of this theory that a longer exposure of skin to UVB zone, to use a word cherished of torrid theory zone, has produced black skin. And Jablonski (2017) concurred, "there has been a cause and effect relationship between UVR and skin pigmentation in human evolution" (p. 6). The causal relationship of black skin with torrid zone is unequivocally assumed, and for this reason, the formula W x L = C employed earlier to visualize Gloger theory at best comes into play. To recap, the formula implies that the amount of the weather (W) multiplied by the length (L) of time produces the color (C) of the skin. When unmixed black individuals move to the poles their skin turns to white after a period of time in low-UVR settings. As discussed above, while the formula may sound ludicrous, it makes perfect sense insofar as the subject unmixed black individuals is replaced by Homo genus. Jablonski added, using a key teaching of torrid zone theory mentioned supra, "that darkly pigmented peoples were found close to the equator; lightly pigmented peoples… were found closer to the poles" (2009, 01:44-50). The same idea was supported by Smith (1787Smith ( /1810. It is worth recollecting here that Jablonski argument is taken squarely from torrid zone theory. As Jablonski (2011) stipulated, By the mid-1700s… the American Samuel Stanhope Smith observed that skin pigmentation showed a pronounced gradient according to latitude, from dark near the equator to light toward the poles… "This general uniformity in the effect," Smith wrote, "indicates an influence in climate, that, under the same circumstances, will always operate in the same manner." (p. 8) The same statement was corroborated by Jablonski and Chaplin (2010a, p. 168, p. 170;2010b, pp. 8962-8963). More specifically, Smith statement quoted above, although not referenced in Jablonski (2011) article, was made in 1787 in the first edition of his book (see Smith, 1787, p. 18), but it was purely and simply dropped in 1810 in the 3rd edition of Smith book (see Smith, 1787Smith, /1810. This was because much at the discontent of Smith, Smith opinion of climate effect with dark skin being closer to the equator and light skin nearer the poles, had met with scathing objection from armies of authors in England and beyond, based on accounts and research received and done around the globe. Sure enough, in the 3rd edition of his book, Smith (1787/1810) markedly revised his statements and toned down his position. Most distinctly, after having been excoriated by "critical reviewers… round the globe" (Smith, 1787(Smith, /1810, see footnote *), Smith (1787/1810) was, in his 3rd-edition book, rather apologetic, stating: "I have endeavoured… to explain the proximate cause of colour… although I should have failed to point out the precise mode in which climate acts, or accurately to have traced the chain of its effects [emphasis added]" (pp. 60-61). Note the qualifier proximate in lieu of definite or absolute cause of color. As acknowledged above, failure to dissect the chain of climate mechanisms and related factors across and within region, latitude, location, group, species, and individuals is what makes torrid zone theory unrepresentative of and inconsistent with the variability proper to the population of the researched and to the world/reality thereof (details below).
While dark or melanized skin is being presented as an evolutionary adaptation of human species to equatorial or savannah intense UVR heat (Jablonski, 2009(Jablonski, , 2011(Jablonski, , 2012a(Jablonski, , b, 2013a(Jablonski, , 2017(Jablonski, , 2018(Jablonski, , 2021bJablonski & Chaplin, 2010a, the reality of human species rebuts such an evolutionary solution/recipe. In effect, the distribution of UVR does not translate into nature, specifically into the global distribution of mammals, birds, humans, and of living organisms. The simple idea that irradiation/combustion destroys organic life just jars with fluidity/richness of life being at its peak on the equator (Humboldt, 1808). A temperature/weather aflame with UVR and thus hot enough to permanently turn (the color of) skin pitch-black would unavoidably destroy organic life in the process. The fact that in equatorial/tropical Africa, infants, pregnant women, albinos, and the elderly of Homo sapiens species have survived UVR intensity with a below-average rate of melanin in their skin demonstrates that the proclaimed UVR-triggered natural selection of black skin did not work/happen. The point being, evolution has to do with the survival of species (Hanel & Carlberg, 2020). This is clearly because the skin of infants, elderly, sick, disabled, pregnant women, and albinos in equatorial Africa is not in any way, shape, or form naturally shielded against the extreme intensity of UVR. Most definitely, no population, race, or species even on the equator survives solely with UVR protection, without vitamin D-supplied nutrition, more so for infants, pregnant women, elderly, albinos, and the sick. Therefore, the argument of black skin being an evolutionary adaptation/solution to the intensity of UVR in equatorial/tropical Africa as arguably demonstrated by NASA map (see Jablonski, 2009Jablonski, , 02:59-03:03, 2011 is not as sound as claimed, and the concept variability defended by Gloger (1833) comes in greater focus. On this note, protection against UVR as an evolutionary reason of black skin was refuted by recent research. For example, Ammitzboell (2020) maintained, It is discussed that the darker skin was developed to protect the person from UV rays that cause skin cancer. But it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success and skin cancer usually affects people after they have had children. (p. 189) Evolutionary adaptation of black skin is contradicted by the fact that reproductive success of human species was not affected by this adaptation. A focus all too reliant on melanin as an ultimate antidote to UVR is not a well-grounded argument, either. Korte and Mandea (2019) waved a flag of caution, stating: "Earth's magnetic field shields our planet against highly energetic particles from the Sun and outer space, which threaten modern technology" (p. 3801). The ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; somehow imminent adversity of UVR tends to cause panic in studies/interpretations of black skin.
Indeed, a recent review by Caro and Mallarino (2020) and by Cuthill et al. (2017) of research done on skin color of mammals shows the skin color of mammals to be a function of crypsis, and not of scorching UVR on the equator. Most strikingly, Caro and Mallarino (2020) suggested that more than a simple cryptic tool "black and white stripes of Zebras are not a form of waning coloration…instead a growing number of studies indicate that stripes thwart attack by disease-carrying biting flies" (p. 362). It is interesting that Zebras, a species endemic to the equator, are endowed with stripes whiter than Whites living/residing in the northern hemisphere. Similarly, in his review of studies applying Gloger theory among birds, Delhey (2019) rejected UV radiation as a mechanism governing bird coloration, with crypsis being the most common mechanism instead. As to humans, the distribution of global UVR is not representative of the variability existing within human species at the time of Homo sapiens and at that of modern humans. To be clear, "hubris easily leads us to forget that Homo sapiens… is one only one of 400 extant species allocated to the order of Primates and just one over 6000 species in the class Mammals [emphasis added]" (Martin, 2015, p. 32). A conclusion or reasoning that each and every individual of Homo genus species is darkly pigmented has yet to be proven, not to mention the wide range of extant hominin species. Also, it seems implausible to present the northern hemisphere as the province/private property of Whites or lighter-complexioned individuals.
Perhaps the most potent refutation of concentrated UVR as an argument for black skin pigmentation, for the theory of geographical gradient of human skin (Jablonski, 2017), and to a great extent for torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 can be seen in four levels. The first level of refutation comes from Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a research. As demonstrated above, Pallas (1780b), an expert with extensive and unparalleled research into arctic regions, showed diversity of traits, skin color, and hair color to be the marker of arctic regions. To add dimension to the refutation, Stanley (1878Stanley ( , 1899, an explorer with remarkable expeditions in the equatorial Africa the birthplace of Homo sapiens, listed a fair amount of aboriginal lighter-complexioned communities on the equator. The second level of evidence sharply refuting UVR argument for black skin pigmentation and for associated theories noted above is with the ubiquity of melanin in nature (Herrera, 2018) and the correlated presence of endemic dark and black fish in Lake Baikal at 53º30N, the oldest, deepest, largest, and coldest lake on earth (Knizhin, Weiss, & Sušnik, 2006;Klump et al., 2020;Zaitseva, Smirnova-Zalumi, & Zakharova, 2008) as well as the dominance of black bacteria/microorganisms in Black Sea (Michaelis et al., 2002;Sergeeva et al., 2014) located at 44º N. Note that Black Sea is the blackest sea on earth with microorganisms interestingly blacker than those found in Lake Victoria located at 1°00S on the equator . Evidence from Lake Baikal and Black Sea was confirmed by Montagna, Prota, and Kenney (1993) research that "all deep-see fish have dark skin. The skin of these fish, which live in darkness, is black or dark-brown as is the fur of most bats, many of which fly at night" (p. 7).
The third level of refutation concerning UVR argument for black skin pigmentation and related theories deals with the fact that despite the omnipresence of pitch-black eyes among species, from reptiles to fishes to insects to birds to mammals and most significantly to humans, eyes of humans living on the equator are not black, According to Kasten and Dürr (2016) as well as Kolga, Tõnurist, Vaba, and Viikberg (2013), black eyes among humans can be found in Siberia the coldest and least UVR-exposed place on earth. While eyes of populations in Siberia can be black, eyes of Blacks living in the UVR-boiling region of Africa are not black or at least no blacker than those found in Siberia among several species including humans. And pitch-black eyes crosscut latitudes in the kingdom of living species. The diversity of color encountered in artic regions (Kasten & Dürr, 2016;Kolga, Tõnurist, Vaba, & Viikberg, 2013;Pallas 1780aPallas , b, 1784Pallas , 1811Pallas /1831a is extremely worthy of note here. The fourth and last level of refutation regarding UVR argument for black skin pigmentation, for the theory of geographical gradient of human skin (Jablonski, 2017(Jablonski, , 2018(Jablonski, , 2021b, and for torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 resides in the existence of pitch-black skin, regardless of races and individuals, particularly naturally occurring on or around elbows, nipples, anuses, arm pits, genitals, knees, ankles, toes, etc. (Cibangu, 2015). Most interesting and indeed refuting is the fact that the color of these areas can vary from pitch-black to pink, regardless of races, individuals, and latitudes. Following from the scenario depicted above, the best consequence would have been the existence of pink nipples, for example, solely among white-skinned individuals living in northern regions as well as the existence of pitch-black nipples solely among black-skinned individuals living in equatorial regions of Africa. Quite conversely, pink nipples or genitals, to mention just one case, exist across latitudes, races, and individuals. Perhaps most antithetical to the thesis of UVR-flooded regions as an evolutionary reason for human skin color is the fact that Tasmanians (Black aboriginals of Australia) had lived in freezing, wintery, and UVR-deficient conditions much longer than Whites had lived in the cold region (see Diamond, 2006, p. 116). The variability of species and of their locations is undeniably proven by the above recent findings.
Closely associated with the geographical gradient of human skin theory is the geographical gradient of human body size/physique. This theory is best summarized by American biologist William R. Leonard (Leonard, 2015) when he reasoned, Among human populations around the world, body size and proportions are strongly influenced by differences in environmental temperatures. Human populations living in cold, artic climates are relatively heavy with large trunks and shortened limb lengths. Conversely, tropical populations are lighter and typically have more linear physiques. These patterns of variation are consistent with the classic "ecological rules" of Bergmann and Allen. (p.

251)
However, a vast majority of Scandinavians along with the populations listed by Gloger residing in the same latitude from Kamchatka (Russia) to Kazan (Russia) to Petersburg (Russia) to Moscow to Dresden (Germany) to Amsterdam to Copenhagen to London to Edinburg (Gloger, 1833, pp. 53-54) display nothing nearing physiques of shortened limbs and large trunks. Research undertaken on various groups of Nordic individuals shows a variety of body size and height (Holmgren et al. 2018;Sorokowski et al., 2020;Zammit et al. 2007), which is a stark contradiction against the claimed gradient of human physique. Human physique is not entirely dependent on latitude. Gloger (1833) finding on the variability seen in Nordic areas was also borne out by Pallas (1780b, pp. 80-81) finding in the Siberian region as well as Humboldt (1831) research. If Gloger arguments were taken seriously, too many cookie-cutter characterizations of black skin could have been avoided, and the complexity of the myriad mechanisms involved in the organic life of black skin would have risen to the fore. Indeed, it has been recently suggested that the genetic basis of skin color is less simple than previously thought and that geographic variation in skin pigmentation was influenced by the concerted action of different types of natural selection, rather than just by selective sweeps in a few key genes [emphasis added]. (Rocha, 2020, p. 77) The statement encountered above is a disproval of an argument made to justify black skin using UVR. The argument was a reaction against Jablonski (2011) who wrote, When people started moving away from very sunny places with high levels of UVB to less sunny places with lower levels of UVB, those individuals who had lighter skin were able to stay healthier and leave more offspring. Evolution was at work again… We see evidence, in fact, that "selective sweeps"greatly accelerated periods of evolution by natural selectionled to genes for lighter skin becoming fixed in the population over the course of just a few thousand years. (p. 9) Selective sweeps did not increase the understanding of black skin and the genes behind it. The truth is, "while continent-scale selective sweeps have been relatively well-characterized, the more subtle interplay between natural selection and the uniquely human impact of culture and demography in shaping pigmentation diversity within smaller regions remains poorly understood" (Quillen et al., 2019, p. 14). Well beyond smaller regions, diversity more exactly variability lies at the heart of every aspect of organic life and physical world, the spinal cord of Gloger theory. It was also suggested that UVR protection is only one among the many functions of skin such as epidermal hydration, proteins and lipids reconstitution, elasticity, etc. (Badreshia-Bansai, Patel, & Taylor, 2016). The complexity of skin is reflected even in its functions. Variability of organic life and the mechanisms involved was a dominant theme of Darwin research on the origin of species since early on, and Wallace (1871, 1878) followed suit. Darwin (1859/1873) confirmed, "natural selection has been the most important, but not the exclusive, means of modification" (p. 4). The statement applies to the manner of understanding and researching black skin formation.

The Second Main Idea is Comparative Evidence
Comparative evidence can be seen as the basis for Jablonski (2017Jablonski ( , 2018 strongest arguments on black skin. The point is that "because skin is mostly not preserved in the fossil record, arguments about the evolutionary causation… have relied on critical examination and integration of pertinent comparative anatomical, physiological, palaeoecological and climatological evidence" (Jablonski & Chaplin, 2017, p. 2). While the reasoning sounds magnificent, its flaw lies in comparing and mixing together incomparable and inseparable units of analysis. To elaborate, there are broadly speaking four disciplines involved in the comparison suggested supra, namely: (1) anatomy; a sample of bones/skull taken from individual A, (2) physiology; a sample of a black skin cut taken from individual B, (3) paleoecology; a sample of a leaf taken from plant A, and (4) climatology; a sample of a temperature taken from spot A. As can be anticipated, the listed samples are units of analysis/research and worlds completely separate and different from one another. The issue was well raised by Smith (2016) and Smith and Wood (2017), namely, how counterproductive and almost impossible is the endeavor to consider a unity of study as representative of the concerned group and of variation (regarding the group and its individuals), not to mention surrounding mechanisms. The idea here refers to Gloger key argument about the complexity of variability mentioned earlier (Gloger, 1833). The variability of one sample and its specific world cannot override or be overridden by that of another. For example, and in line with Gloger (1833) thesis homing in on variability, (a skull of) individual A and (a leaf of) plant A are inextricably unique although they might be related, and cannot be lumped together as one species per location, weather, or latitude. More precisely, considering by way of illustration individual A as a whole in and by himself, his skull cannot be separated from the whole (i.e., world around it and the rest ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; of the individual's body). The same is true of black skin. Black skin (i.e., its ingredients and nature) cannot be separated from the whole.
A reflection fairly supportive of comparative study/evidence adopted by Jablonski is the one that reads as follows, Comparative study of the human melanocortin 1 receptor (MC1R) locus demonstrated that the timing of evolution of permanent, dark, eumelanin-rich, skin pigmentation coincided with the evolution of functional hairlessness and increased density of eccrine sweat glands early in the history of the genus Homo, approximately 1.2 million years ago or earlier… Adaptive evolution for sun-resistant alleles of the MC1R locus appear to have occurred, therefore, when early members of the genus Homo became mostly hairless and highly physically active inhabitants of open savannah environments in Africa. (Jablonski, 2017, p. 2) A similar argument was made in detail by Jablonski and Chaplin (2010a, pp. 167-183) and Jablonski (2018, p. 30). By all odds, the dating of MC1R has helped deduce the (time of) dark skin of Homo genus, which in turn has been described as a protective tool against sun-drenched environments of equatorial Africa. While comparative study can be a powerful tool for a researcher to make an argument, such as dating the protein MC1R in hominins, it is not a valid/scientific indicator of representativeness for the researched and their world. Indeed, the dating of MC1R at around the time of Homo genus presence in equatorial Africa not only falls short of representing the variability of human species at that specific time/period and the world thereof, but comes in sharp contradiction with the ubiquity of melanin or dark/brown pigment in nature (Galvá n & Solano, 2016;Herrera, 2018). The concept hairlessness of Homo genus is not without flaws, either.
Wallace (1871), a renowned co-discoverer of evolution theory with Darwin, quite empathically stated, "man's naked skin could not have been produced by natural selection [emphasis in original]" (p. 347). In more ways than one, naked skin poses no small health hazards in a savannah or forest setting; a setting famed for irresistibly rapidly reproductive organic life such as bugs, germs, pollens, etc. (details below).
Variability has been raised and/or demonstrated on multiple fronts by Gloger (1833) as well as his research mentors Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a and Humboldt (1808Humboldt ( , 1831. To date, variability --also called endogeneity or sample representativeness to highlight all factors endogenous or proper to a given phenomenon or population and the world or context thereof --is key in defining a research impact. Research impact is measured by a research's "sample representativeness, meaning that when the process of selecting the sample has been performed properly, the sample will often have characteristics similar to those of the population [emphasis in original]" (Sotos et al., 2007, p. 101). Recent research materials identify variability as a researcher's ability to produce results fully representative of and/or consistent with the variability pertaining to the population of concerned participants and to the reality or world in which the participants are situated or live. As Lichtenstein (1833) unambiguously acknowledged in the foreword to Gloger (1833) work, [Gloger] immer das Verdienst beimessen dürfen, den… von unsrer Zeit dringend gefordeten Untersuchungen… nach einer neuen Richtung die Bahn gebrochen zu haben [one would always give to the author of this paper [Gloger] credit for having broken fresh ground with the pressingly required research of our times… in the path toward a new direction]. (p. iv)

Man wird dem Verfasser dieser Schrift
Listened to closely, Gloger was a powerful mover of skin color research, particularly regarding the relations between environment and species. In this respect, there are myriads of inconsistencies plaguing present day skin color scholarship about black skin.

The Last and Third Main Idea is High Physical Activity
High physical activity of Homo genus underlies Jablonski (2017Jablonski ( , 2018Jablonski ( , 2021b forceful arguments on black skin. The argument is premised on increased density of eccrine sweat glands early in the history of the genus Homo, approximately 1.2 million years ago or earlier… when early members of the genus Homo became mostly hairless and highly physically active inhabitants of open savannah environments in Africa. (Jablonski, 2017, p. 3) The same idea was justified by Jablonski and Chaplin (2017, p. 3), Jablonski (2018, p. 30), andJablonski (2021b, p. 707). While the argument is fascinating, high physical activity is downright unworkable and unwarranted when it comes to the forces/factors at play in a savannah and forest natural setting. For example, one cannot easily run or walk on sand or on pointed, uneven rocks. To explain, sand, mud, dead leaves, hanging and entangled shrubs, broken branches, and fallen trees, to name a few features of a savannah or forest, are incompatible with, disruptive of, and hazardous to a normal and more so to a high physical activity of running and walking. Moreover, as one is in the midst of all the activity of running fast, bugs or moist as well as dust from sand, clay, wood, hay, and grass pollen only make the likelihood of injury and damage to eyes greater, and there is also a reasonable chance of choking and sneezing as the mouth and nostrils tend to remain wide open for better oxygenation. In all probability, untreated/unprepared terrain poses a nonnegligible hazard to ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; both shod and unshod runners or walkers.
Even more hazardous, naked skin is not at its best in a savannah or forest on the equator, considering on the one hand the richness of microorganisms, pathogens, bugs, etc. in that part of the world (Humboldt, 1808(Humboldt, , 1831 and on the other hand the moisture constantly found/replenished in skin (Jablonski, 2013a, p. 2). The moisturizing aspect of skin was asserted by Yadav et al. (2019, p. 2) and Badreshia-Bansai, Patel, and Taylor (2016, p. 67). As largely shown above, no naked skin -human, animal, or plant --remains secure in the open air, across latitudes, species, and individuals. Wallace (1871) observed that indigenous peoples found in tropical, equatorial forests were seen wearing fur and/or large leaves to protect their bodies/skins. This would not have happened if their skins were adequately shielded by natural selection. One classic example on this note is with human swollen lips, a characteristic singularly distinguishing humans from (the lips of) their ancestors primates according to Blumenbach (1775Blumenbach ( /1795). Yet, human lips are one of the most UVR-unprotected organs of humans, noted for its varying color across races and individuals (from brown to pink to black to red to yellow), and also an organ known for being the most exceptionally vulnerable to ambient air across latitudes and climates, both indoors and outdoors. If the melaninization of skin in hominins and modern humans had happened as claimed by skin color scholars (Jablonski, 2009(Jablonski, , 2011(Jablonski, , 2012a(Jablonski, , b, 2013a(Jablonski, , 2017(Jablonski, , 2018(Jablonski, , 2021bJablonski & Chaplin, 2010a, lips would have been the most melanized organ of humans because lips tend to be particularly susceptible to ambient air, regardless of temperatures and latitudes. Therefore, the claimed melaninization of skin is not an effective natural protection of skin. As Darwin (1859/1873) reminded skin color researchers earlier, natural selection although important is in no way the sole means of species modification. One other distinguishing characteristic of humans full of interest about naked skin of Homo genus, as Wallace remarked, is, In man the hairy covering of the body has almost totally disappeared, and, what is very remarkable, it has disappeared more completely from the back than from any other part of the body. Bearded and beardless races have the back smooth… the back, and especially the spinal cord region, is absolutely free, thus completely reversing the characteristic of all other mammalia. (Wallace, 1871, p. 345) With the back being most vulnerable to rain, wind, and cold, particularly in the spinal cord area, the idea of naked skin and eccrine glands as a means of natural selection makes no sense. Other mammals have their spinal areas well protected with fur or scale.
As an illustration, concerning the forest in Africa in which Homo genus are claimed to have started or been born, Stanley (1899) testified, And all this time the trees kept shedding their dew upon us like rain in great round drops. Every leaf seemed weeping. Down the boles and branches, creepers and vegetable cords, the moisture trickled and fell on us.
Overhead the wide-spreading branches, in many interlaced strata, each branch heavy with broad thick leaves, absolutely shut out the daylight. (p. 101) Such a context filled with hanging twisted vegetable cords and creepers is completely inadequate and indeed dangerous for any form of high physical activity, much less walking and running. To make things even more dangerous, regarding the soil similar to that of a savannah, Stanley (1899) asserted, We, accustomed to rapid marching, had to stand in our places minutes at a time, waiting patiently for an advance of a few yards, after which would come another halt, and another short advance to be again halted… The path soon became a stiff clayey paste, and at every step we splashed water over the legs of those in front, and on either side of us. To our right and left, to the height of about twenty feet, towered the undergrowth, the lower world of vegetation.
The soil on which this thrives is a dark-brown vegetable humus, the dé bris of ages of rotting leaves and fallen branches, a very foreing-bed of vegetable life, which, constantly fed with moisture, illustrates in an astonishing degree the prolific power of the warm moist shades of the tropics… Every few minutes we found ourselves descending into ditches. (pp. 101-102) The texture and density of the undergrowth arising from the soil, marshy, muddy, clayey, slippery and awash with broken branches defeat the purpose of walking and running. As Hunt (2015) indicated, "bipedalism is not only slow and unstable compared with quadrupedalismunlike most adaptations (say, adaptions to chewing harder foods), it is clumsy and inefficient in its earliest evolutionary stages" (p. 108). Human feet do not carry as much grip as the feet of birds, mountain goats, and cats do, to name a few. Therefore, human feet are ill-equipped on branches, rocks, holes, bumps, slippery soils, dead leaves, etc. In a forest or savannah, wet and dry leaves constantly cover the soil, leaving it slippery. Humans don't jump while running; jumping is essential in catching prey in a savannah or forest. Bipedalism is the least common way of motion in the kingdom of livings. Primates who are bipedal are excellent climbers whereas humans are not. Because bipedalism is unusual, clumsy, and imbalanced compared to quadrupedalism, crawling, or flying, there is a far greater likelihood of injury of ankles, toes, knees, and hips, which can happen regardless of shod or unshod feet, of heathy or unhealthy persons. In those days (i.e., Homo sapiens'), people didn't have surgery or ice pads. ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; According to Jablonski and Chaplin (2010a, 2021b, high physical activity to explain black skin evolution is closely correlated with eccrine production because of hairlessness or human naked skin seen with Homo sapiens. However, regardless of age, race, latitude, mobility, health, and location (i.e., outdoors or indoors), human skin invariably suffers from cracks, blisters, bruises, cuts, blotches, etc., all of which constitute perfect targets for germs and bugs, not to mention that band-aids and baby powder were unavailable during Homo sapiens' days. Perhaps the biggest shortcoming with the argument of high physical activity is with the hunting duty of Homo genus being described as part of and reason for high physical activity (Jablonski, 2017(Jablonski, , 2018(Jablonski, , 2021bJablonski & Chaplin, 2010a. This argument can be rebuffed using two facts. The first rebuffing fact is that high physical activity or hunting came quite late in the history of Homo genus. The reason is that "no actual fossil evidence of tools designed for hunting exists earlier than approximately 400, 000 years ago" (Sussman & Hart, 2015, p. 75). This shows that the melanization of human skin due to high physical activity is a moot point. "In fact, when we look at the fossil evidence, hunting may have come quite late in our human family. Interpretations of hominin behavior, therefore, should be conservative and cautious" (Sussman & Hart, 2015, p. 74). The behavior of high physical activity for early Homo genus is unjustifiable considering the wild/unarranged terrain of a savannah or forest. Perhaps more clarifying is the idea that hunting is not as much a characteristic of humans as agriculture (i.e., plowing, shepherding, gardening, etc.), metallurgy (e.g., mining, foundry, alloyage, etc.), and art (e.g., sculpture, painting, jewelry, etc.). Monkeys or primates, the ancestors of humans, do not hunt, and although as noted earlier monkeys are skillful climbers, humans are not.
The second rebuffing fact is that, even if hunting were to be taken as part of Homo genus activity, the argument is still unconvincing since hunting is not the same as running fast, supposedly to catch prey. Curiously enough, the synonyms of the English verb to hunt are: to look, to search, and to seek (Cambridge Advanced Learner's Dictionary, 2013), and not to sweat, to run, to race, to dash, etc. It is like saying that fishing consists of swimming fast in order to catch fish. No wonder the concept hunting often goes hand in hand with the concept gathering because one cannot gather while running and one cannot run while gathering, hence the phrase hunters/gathers. Taking everything into consideration, one realizes that running is well out of the picture partly because gathering, especially of food, has to be carefully slow/selective. Consider even wild cats (e.g., lions, jaguars, leopards, tigers, etc.) and wild dogs (e.g., coyotes, foxes, jackals, wolves, etc.), known to be among the fastest runners in the kingdom of animals: they do not spend days and/or hours running fast, panting/perspiring, in order to hunt prey. On the contrary, wild cats and wild dogs (Castelló, 2018(Castelló, , 2020Driscoll, Macdonald, & O'Brien, 2009;Hunter, 2015;Spencer, Crowther, & Dickman, 2014) hide and move slowly, cunningly, and surreptitiously to entrap and capture prey; thus running if it ever happens during hunting, is done in the blink of an eye. These hunting animals often times give the impression of being deeply asleep, motionless, inoffensive, and inattentive only to jump and catch prey in a fraction of a second.
For instance, describing Hadza people, famous hunters/gathers of Tanzania, Marlow (2010) underlined, Hadza men rarely run. They may run briefly to get a second shot at a large herd. Occasionally, when they see a small animal like a hyrax, they may run to cut it off before it can reach its home in a rock [emphasis added]. (p.

118)
Remember that this is one of the species-richestso to speak --areas on the globe, therefore running or high physical activity is uncalled for in order to find food/prey. Just as one does not need to sweat or swim fast in order to find fish in the ocean, so too one does not need to sweat in order to hunt prey in a forest or savannah. One paramount thing to acknowledge is that evolution concerns/affects a whole species (Ammitzboell, 2020;Hanel & Carlberg, 2020). But still, women, children, disabled, and elderly do not usually hunt, while being every day exposed to and grilled by intense UVR close to the equator. This means that their skin could and should not have turned black. Therefore, hunting and high physical activity as evolutionary solutions/adaptations are unsuitable, at least inadequate for the variety of human species dealing with this specific environment, variety being a central argument of Gloger.
Another no less gripping argument arising from high physical activity is that of vitamin D and folate regulation among hominins and modern humans. The classic explanation given here is that "the primary role of dark constitutive skin pigmentation in hominin and modern human evolution is that of a natural sunscreen to conserve folate" (Jablonski, 2017, p. 3). The explanation has received support at various levels, as shown by Jablonski (2012a, p. 11), Jablonski andChaplin (2017, p. 3), Kelly and Jamoussi (2016, p. 6), and Taylor and Kyei (2016, p. 9). This explanation cannot help but bolster torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810 in general and the formula visualizing Gloger (1833) theory in particular (see supra). Jablonski (2017) alleged that "when we consider the evolution of skin pigmentation, it is clear that long-term occupation of non-tropical latitudes would not have been possible without loss of some constitutive eumelanin pigmentation in order to prevent the serious sequela of hypovitaminosis D" (p. 5). As can be realized, the higher is the amount of pigment/melanin in a skin the more deficient in vitamin D is that skin, which in this case is black ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1;2022 63 skin.
Meanwhile, the vitamin D and folate argument to account for black skin has been disproven extensively in recent studies. Thus, Jones, Lucock, Veysey, and Beckett (2018) noted, The vitamin D-folate hypothesis and related theories propose that skin pigmentation evolved to regulate the biological effect of differing UVR levels in different regions of the globe… However, the migration of human populations across large distances over the last several hundred years has created an evident mismatch between the adapted skin types of individuals and their UVR environment. (p. 7) Similar research was conducted by Elias and Williams (2018, p. 2). A mismatch has equally been shown regarding the distribution of vitamin D across the globe. This research has been undertaken by Elias for more than a decade (Elias & Williams, 2013Elias, Williams, & Bikle, 2016). Natural selection of skin pigmentation has been immensely disputed. "Current theories for the development of epidermal pigmentation in hominins are problematic… Latitude-dependent pigment dilution to facilitate cutaneous vitamin D3 (VD3) synthesis is also problematic" (Elias &Williams, 2015, p. 273). Latitudinal skin pigmentation is rife with inaccuracies.
The argument of Vitamin D for skin pigmentation was further rebutted using extensive empirical research. In minute details, Elias, Williams, and Bikle (2016) asserted, Given its importance… natural selection surely would have evolved more efficient regulatory mechanisms than latitude-determined gradations in skin pigmentation… In fact, pigmentation did not lighten in a predictable fashion as humans emigrated out of Africa … Very fair pigmentation evolved solely in populations residing far to the north in Europe… long after they had migrated out of Africa. Likewise, virtually all other Eurasian populations display intermediate shades of pigmentation, independent of latitude… Consider also that melanin is a relatively inefficient UV-B filter in comparison to another endogenous mechanism that is much more efficient; that is, transurocanic acid (t-UCA), which intercepts well over 50% of incident UV-B, even in darkly pigmented skin. (p. 756) Elias, Williams, and Bikle (2016) elicited, Moreover… even dark-skinned individuals, living at latitudes comparable to New England, can generate sufficient vitamin D during normal summer seasons… Finally, and perhaps most importantly, melanin exists in many non-sun-exposed organs of mammals, as well as in many pro-and eukaryotic organisms … where it must mediate other functions, known or unknown. Even in mammalian skin, pigmentation modulates numerous other functions, ranging from insolation to camouflage. (p. 756) Elias research can be described as the most comprehensive and solid repudiation of the claimed skin pigmentation of hominins. The key idea being that regarding skin natural selection cannot be reduced to melanization.
The fact that both folate and vitamin D are related to a wide variety of cancers and chronic diseases debunks the evolutionary thesis of black skin as a byproduct of vitamin D and folate adaptation. Perhaps the biggest rebuttal against the vitamin D and folate argument is with what is called the vitamin D paradox. As Vieth (2020) elaborated, The vitamin D paradox relates to the lower risk of osteoporosis in people of sub-Saharan African ancestry (Blacks) compared with people of European ancestry (Whites). The paradox implies that for bone health, Blacks require less vitamin D and calcium than Whites do. (p. 617) To a great extent, the paradox cited above has led to relentless reexamination of Vitamin D argument regarding black skin. Consequently, Hanel and Carlberg (2020) contended, "thus, archeogenomic data as well as comparisons of today's populations did not provide any indication for an evolutionary pressure for light skin created by the need for vitamin D" (p. 871). Neither vitamin D nor folic acid amount to sufficient/cogent evolutionary grounds for black skin.
black skin is not as sun-proof as alleged. As Ansari, Le, and Harvey (2017) cautioned, The American Academy of Dermatology (AAD) recommends that all individuals apply sunscreen prior to outdoor exposure regardless of age, gender, or race… Sunscreens should be applied 15 minutes prior to going outdoors, and reapplied approximately every two hours, or after swimming or sweating… Guidelines also recommend usage of protective clothing such as long-sleeved shirts, pants, and wide-brimmed hat. (p. 58) This recommendation across races and skin types is corroborated by Solano (2020) finding that "sun exposure without skin protection can be harmful anytime and anywhere" (p. 5). The finding comes as a blatant repudiation of the pretended sunscreen property of black skin in hominins and modern humans living on the equator. The finding has reversed the long-standing misconception that solely light skin was sensitive to UVR. As Del Bino, Duval, and Bernerd (2018) underscored, "while fair skins were in the past considered as the only sun sensitive phototypes due to higher skin cancer prevalence, nowadays, concerns regarding pigmentary problems of people with darker skin are emerging" (p. 26). Sunscreen protection/property is no longer a valid evolutionary characterization of black skin. For example, infectious and/or cancerous conditions can occur and are more difficult to diagnose in black-skinned people in large part because, as Abdulhak and Moiin (2020a, b) demonstrated, black-skinned patients are rare in most hospitals and medical practices. The lack of diagnosis or knowledge about the conditions of black-skinned individuals leads to a mischaracterization of black skin. Adding a dynamic to this dilemma, most clinical skin conditions tend to be consistent among skin types (Hines & Moiin, 2020;Lawrence & Moiin, 2020a, b). This has created grave misunderstandings about black skin. One of the most common misunderstandings or misrepresentations of black skin resulting from the hypothesis of vitamin D is the idea that "the relationship between skin color and skin cancer is well established: the less melanin in one's skin the greater the risk for developing skin cancer" (LaBerge et al., 2020, p. 69). While such an idea is empirically established, the blunt reality is that black skin or melanin is not even among the palliatives or cures against the symptoms of regular diseases such as nausea, headache, fever, etc., not to mention cancer itself.
Vitamin D was also correlated with an increase in caesarean section at delivery, across races (Keats et al., 2021). Such evidence gives an indication that Vitamin D is not reducible to black skin formation. One clarification needing mention here is that some diseases can be more pronounced in certain categories such as age, gender, height, etc. than in others. One case in point is that of ovarian cancer and breast cancer observed to be more frequent among White women than Black women and/or other ethnicities (Chapman-Davis et al., 2020). Thus, the claimed low concentration of skin cancer among Blacks is not something completely unnatural nor something caused by the blackness or darkness found in an individual's or a population's skin.

Pathways of Future Research on Skin Color
A number of lessons can be drawn from Gloger (1833) theory and its historical background. Just like organs, for example, eyes, ears, teeth, etc. respectively require a stand-alone department or scientific field to be studied, so does skin. It would thus be misleading, counterproductive to forego the complexity of skin and the color thereof. While the racially based dichotomy blackness vs whiteness was found to plague skin color research (Jablonski, 2021a), entire notions as well as misused and inappropriate narratives continue to beleaguer the understanding of black skin and the research of it. Such practices tend to poison the working atmosphere of black skin research. As paleoanthropologists Smith and Wood (2017) warned, "we generate comprehensive narratives knowing that we do not have all of the relevant data… There is much we would like to know about human evolutionary history, but wanting to know something does not make it knowable" (p. 677). As a matter of fact, notions such as equator, UVR, heat, global map, hairlessness, etc. have been used without relevant data, taken out of their context, and twisted to support (the supremacy of) white skin, and further obscure black skin complexity. Perhaps one of the most detrimental pitfalls besetting black skin scholarship sits in its methodology. Influential tables (Jablonski, 2009;Jablonski & Chaplin, 2010a, b) used to explain the gradient of human skin or of global latitudinal skin variation are nowhere close to required standards for the construction of tables or graphs nor to standard research method (Babbie, 2021). A large part of the shortcoming is that university interpretations of black skin arose in prejudice with the Linnean classification (1735/1758), Kant teachings (1775) on different human races, and torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. Current skin color research has not done much to turn the tide. A larger part of the shortcoming is a lack of data covering the time and site of Homo sapiens (and even modern humans) in Africa. Perhaps the largest part of the shortcoming is that existing skin color research relies nearly exclusively on comparative evidence. However, comparative evidence is not a standard research method of quantitative research and qualitative research (Babbie, 2021). What makes comparative evidence, at least as it is applied in skin color research, less than convincing is the lack of needed relevant data.
Methodology is a term generally conceived as covering subjects/courses of quantitative research and qualitative research, which yield results as representative as possible of and/or consistent with selected participants and their worlds on the one hand, depending on a researcher's preference, or as deep-drilling as possible into the lives of selected participants and ijb.ccsenet.org International Journal of Biology Vol. 14, No. 1; their worlds, on the other hand (Babbie, 2021). Thus, methodology enables a researcher to further the understanding of a phenomenon's or reality's variability. The idea of species was a way for Gloger (1833) to address variability. Gloger insisted on the interplay between biology (e.g., black skin) and environment (e.g., climate) to warn authors against cookie-cutter approaches that wipe out specifics/variability across latitudes and weather conditions. The lack of "a global map that is comprehensively and individually representative of human skin variation [emphasis in original]" (Cibangu, 2015, p. 53) is living testimony to the fact that methodology merits attention in skin color discourse. Another testimony to the significance of methodology in skin color scholarship is with the erroneous and inappropriate narratives/scenarios of high physical activity or vitamin D regulation to explain the black skin of Homo genus. Another even starker testimony is with existing limited data regarding geographic populations of skin color variation (Jones, Lucock, Chaplin, Jablonski, Veysey, Scarlett, & Beckett, 2020, p. 2) and current scant knowledge on skin microbiome (Jablonski, 2013b). Since the last several decades quantitative research and qualitative research have increasingly been listed across universities and departments around the world as required subjects for the conferment of degrees.
Skin color research is called to be a type of research aiming to reflect the representativeness of and/or in-depth immersion into the lives of concerned participants and their worlds. Just as Gloger was unreservedly self-reflexive about his own research, it is time for skin color researchers to go past researchers' biases, labs, agendas, terminologies, etc. to live up to the standards of representativeness about and/or the unraveling of the life of the researched and of related world. Only then can skin color research produce research, narratives, or scenarios representative of, consistent with, and/or deep-drilling into the lives of black-skinned species/livings and their worlds. This is also one more reason for skin color researchas Smith (1787/1810) a leading figure of torrid zone theory acknowledged --to tease out piece by piece the mechanisms involved in climate effects, a condition proposed by Gloger (1833) to tackle variability. However, as indicated earlier, Jablonski (2011) referenced Smith (1787) for an argument on equator-based skin color that Smith (1787/1810) already retracted in recognizing the necessity of variability. Comparative study/evidence can be useful in posing a research question, but as claimed above it is not a standard method of representativeness/quantitative research or deep-drilling discourse/qualitative research about the researched and their worlds. Existing narratives alluding to the so called out-of-Africa migration of Homo genus (Jablonski, 2009(Jablonski, , 2011(Jablonski, , 2012a(Jablonski, , b, 2013a(Jablonski, , 2017(Jablonski, , 2018(Jablonski, , 2021bJablonski & Chaplin, 2010a obscure rather than illuminating the hardships/struggles/realities proper to the worlds of early and modern humans. A good start for a rethink of methodology embraced in skin color studies is perhaps with terminology as Jablonski (2013b) recognized, Skin science is hobbled by old practices and vocabularies, starting with the very concept of "ethnic skin". For example, the same skin phototypes can be produced by completely different sets of pigmentation genes… but phototypes continue to be used because they are durable traditions.… The importance of future discoveries in human skin diversity will be grasped fully and acted upon only if we have a sophisticated vocabulary to match our science. (p. v) As stated above, variability of pigmentation might be concealed under a veil of commonly used broad-brush concepts. Nevertheless, the lack of variability-appropriate terms admitted to be plaguing skin color discourse as suggested by Jablonski (2013b) above (and also Jablonski, 2021a, p. 444) is refuted by the well-known tendency of biology and climate sciences to use neologisms for newer, specific phenomena or topics. As a quick illustration, it is apparent even to lay people that every new hurricane or disease to give just one example among others has a name/terminology ascribed to it. One unfavorable prevailing condition of black skin research is that black skin is generally subsumed under broad-scoped headings such as "skin of color… ethnic skin, pigmented skin, and darker skin" (Kelly, Taylor, Lim, & Serrano, 2016, p. xxi). While these concepts and associated organizations can be powerful tools in developing an awareness of nonwhite-skinned populations, they tend to dilute the particulars/characteristics of black skin. Much of the reason is that "the lexicon of human diversity is replete with descriptors that evoke pejorative associations" (Jablonski, 2021a, p. 444), not to mention the narratives misused and concepts twisted in prestigious publications about black skin and skin color. With prejudice lingering behind, the quandary of skin color research is huge. The quandary of skin color research has been best summarized by Wood (2010) saying, "But when all is said and done a taxonomy [e.g., Homo sapiens] is just a hypothesis; it is not written on stone tablets" (p. 22), and by Jablonski (2012a) adding, "we can only speculate" (p. 38).
Interpretations of black skin are nothing less than culturally motivated and constructed speculations. As Jablonski (2021b) warned, "we cannot assume that the appearance, genetic composition, sun exposure habits, or UVR skin reactions of humans today are the same as those of our ancestors in prehistory" (p. 709). For example, hands, eyes, and hair, among others, pose the toughest challenges to traditional skin color as they completely defy the thesis of latitudinal gradient for human skin color. Perhaps the toughest challenge for skin color research resides in the use of arguments and narratives that are substantially at odds with the reality of the phenomena being researched or talked about (i.e., savannah, forest, running, feet, naked skin, etc.). These and many challenges are also aggravated by the inadequacy of extant nomenclatures for the description of skin color (Dadzie, Sturm, Fajuyigbe, Petit, & Jablonski, 2022), more especially black skin.
Prejudice represents an inconceivably huge challenge derailing black skin research. While temperatures in the equatorial zone, for example, are beyond a shadow of a doubt demonstrated to be lower than those on the east coast of North America as Gloger (1833, p. 59) noted, with no sunshine, again as Gloger (1833, p. 47) and Stanley (1899, p. 101), among others, observed, prejudices of intense heat and sunshine regarding equatorial Africa persist among high ranked skin color scholars (Jablonski, 2009(Jablonski, , 2011(Jablonski, , 2012a(Jablonski, , b, 2013a(Jablonski, , 2017(Jablonski, , 2018(Jablonski, , 2021a. Resulting from these and many prejudices is an unquestioned blanket application of concepts proper to manmade parks and woods seen in Western Europe and North America to explain Homo sapiens behaviors in savannah or equatorial Africa. It follows that there is no apparent reason for "sustained muscular effort involved in long-distance walking and running in hot conditions" (Jablonski, 2018, p. 30) in areas of wild, unprocessed, rocky, thorny, and slippery terrains, entangled with hanging bushes, grass, and fallen, broken branches, with no trails, paths, or hiking equipment (i.e., boots, gloves, knives, repellents, pairs of glasses, compasses, handguns, first-aid kits, etc.). It is thus unthinkable that areas noted for the highest richness of species would require long-distance walking and running in order for Homo sapiens and in fact for any individuals to find food. It is like saying as presented supra that in order to catch fish in the ocean one would need exhaustive/long-distance swimming, not to mention the consequences/hardships arising from naked skin, bare feet, bare hands, bare eyes, etc. As elicited earlier, the prejudices bedeviling skin color research derive in large part from the Linnean and Kantian classifications (Kant, 1775;Linnaeus, 1735Linnaeus, /1756) coupled with torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810. There is no such a thing as an animal or prey in the kingdom of living species that is known for being caught by running (fast) after it. The pathways of future research remain as a timely reminder of the limitations to overcome/acknowledge to move forward with this paper research/review.

Conclusion
While it is generally believed that humans are equal, erroneous attitudes toward, unreasonable concepts for, groundless theories of, and prejudiced narratives about black skin continue to be held by mainstream publication circles. Black skin is being dismissed as unfit and outdated for standard review/research while the concepts equator and UVR, among others, have been removed from their proper contexts and disciplines only to be wrongly reduced and applied to black skin. To make this worse, newer research has shown that the birthplace of Homo sapiens is neither on the equator nor in the savannah region of Africa.
The biggest contribution of Gloger, although commonly unrecognized, is a vehement disavowal of equatorial heat and accompanying human gradient of skin color. Part of the problem might be that Gloger (1833) himself started (the problem) by posing a research question or premise, popular during his time, broaching climate-carried color of skin. However, Gloger was never able to find, undertake empirical research to support such a premise, and he was seconded by his mentors (Pallas 1780a(Pallas , b, 1784(Pallas , 1811(Pallas /1831aHumboldt 1808Humboldt , 1831. From the Linnean system (Linnaeus, 1735(Linnaeus, /1758 to Kant (1775) summer lectures for over two decades and to Agassiz (1850) classes for more than two decades, the notion black skin has been presented with not only misconceptions, but misleading attitudes as well as misapplied and wrong concepts. The notion black skin was further obscured by that of Caucasian race (Blumenbach, 1775(Blumenbach, /1795) and by the captivating development of torrid zone theory (Smith, 1787(Smith, /1810. Adding to the hysteria, the Industrial Revolution provided sterling, new technologies never thought of before such as telegraph, steam engine, electricity, etc. which unimaginably bolstered the on-going transatlantic trade of slaves and its already widespread and university-endorsed prejudices on black skin. Unlike in ancient society, however, relatively from the turn of the 18th and 19th centuries onward, unchallenged and often unconfessed narratives of black skin evolution and explanation continue to be propelled and believed across eminent publication outlets and public policy agencies. In the matter of narratives/arguments deploying high physical activity of hominins in UVR-sizzling savannah or equatorial forest of Africa to characterize black skin, it warrants being borne in mind, for example, that human feet offer absolutely no grip in forest or savannah conditions (i.e., ditches, rocks, thorns, fallen trees, etc.), let alone human naked skin, ears, eyes, and noses are naturally ill-shielded against pollens, biting bugs, winds, and similar savannah or forest features. The recently increasingly accepted idea of multiple dispersals of Homo sapiens individuals out of Africa imply multiple reasons beyond natural selection.
Quite simply, the hottest temperatures would irreversibly destroy life so as to turn skin into a pitch-black-colored organ. Yet, equatorial/savannah region is recognized for the highest fluidity/richness of organic life (Humboldt, 1808;Stanley, 1899). Climate effects have been acknowledged since Antiquity, with no deprecation against or limitation to a given geography-bounded skin color or nation. Antiquity writings display a highly neutral respect and presence of black skin across latitudes and places. The respect was also heightened by an extensive existence of aboriginal Black communities in North Africa and across Asia (Blakely, 1986;Brook, 1999Brook, /2018Herodotus, ca. 425 BC/1950, ca. 425 BC/1957, ca. 425 BC/1960Humboldt, 1808;Job 30:30 Hebrew Interlinear Bible;Pallas, 1780b;Lamentations 4:7-8, 5:10 Hebrew Interlinear Bible), well beyond equatorial Africa to which torrid zone theory (Blumenbach, 1775(Blumenbach, /1795Smith, 1787Smith, /1810) and slavery-based transatlantic trade (Kendi, 2017) have tended to restrict black skin. The respect of black skin has survived quite persistently till the late 19th century, when a full-blown torrid zone theory emerged. Even in the 19th century onward, torrid zone theory and similar theories such as geographical gradient of human skin theory (Jablonski, 2017(Jablonski, , 2018(Jablonski, , 2021b were met with virulent, unyielding rejection. The rejection was further exacerbated in the late 18th and 19th centuries, when the pioneers of the measurements and observations of the equator and latitudinal differences never reduced the concepts heat and radiation on the equator to a given location or skin such as equatorial Africa or black skin (Humboldt, 1808(Humboldt, , 1831La Condamine, 1745). While Gloger (1833) clearly postulated Gloger theory invoking the idea of climate-bleaching effects, he subsequently fell short of supplying/finding empirical evidence. Pallas did the same when he (Pallas, 1780a) somehow posed the idea of region-based and species-limited climate effects only to completely revoke it with extensive empirical research (1780b). This might perhaps be one reason why both Gloger and Pallas did not finish up their works before they died as promised.
Indeed, the arguments and conclusions critically advanced by Gloger himself have laid to rest Gloger theory as well as torrid zone theory and gradient of human skin theory, bringing into greater focus (Humboldt, 1808(Humboldt, , 1831 latitudinal gradient theory as well as Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a position of variability about climate effects. The fact that the seminal writings of Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a, Gloger (1833), and to some extent Humboldt (1808Humboldt ( , 1831, Stanley (1878Stanley ( , 1899, Wallace (1871Wallace ( , 1878, and Antiquity authors (Bunson, 2002;Foster, 2001) are unknown or uncited among skin color readership has led to significant misleading interpretations of black skin and its ecological setting. Hairlessness alongside high physical activity of Homo sapiens were downright invalid as factors of natural selection for black skin, so were tropical light and heat, the favorite concepts of torrid zone theory. Neither Pallas nor Gloger nor Humboldt ever used the concept Caucasian in describing animal as well as human species and subspecies. Neither of them devised a global map of skin color (i.e., for birds, animals, or humans), either, despite their unrelenting penchant for travel, unparalleled geographical knowledge, and the spectacular tools at hand. Neither of them defined the equator and UVR as the yardstick of black skin., but rather as the yardstick of organic life diversity/richness. This is particularly significant because both Pallas and Gloger figure among some of, if not, the most authoritative biologists/naturalists of Siberian region. The concept Caucasian is anything but false so is the narrative regarding high physical activity of Homo genus in order to justify black skin. Narratives employed for the natural selection of hairlessness and bipedalism are void of common sense. Neither Antiquity authors (Brown, 2001;Foster, 2001;Matić, 2020), nor Herodotus (ca. 425 BC/1950, ca. 425 BC/1957, ca. 425 BC/1960, nor Darwin (1859Darwin ( /1873Darwin ( , 1871Darwin ( /1889, nor Wallace (1871Wallace ( , 1878, nor Pallas (1780aPallas ( , b, 1784Pallas ( , 1811Pallas ( /1831a, nor Humboldt (1808Humboldt ( , 1831, nor Gloger (1833) ever found in their trips and/or research the uniformity or gradient of human skin according to the equator or latitude, an idea largely defended by torrid zone theory (Smith, 1787(Smith, /1810, let alone Smith (1787/1810) himself, later and perhaps for the rest of his life, decidedly retracted his stance on black skin.
This implies that the most tested and increasingly widely accepted pattern, interpretation, or theory that can be used to fully explain/understand black skin in particular and skin color in general is latitudinal gradient theory. As seen with latitudinal gradient theory, (organic) life is too complex a phenomenon to be reduced to a single evolutionary mechanism/hypothesis/theory: black skin too can no longer be lodged in a single, isolated, and all-size-fit mindset/narrative. Rather skin (color) ought to be unraveled in an inclusive multifaceted mix of mechanisms or hypotheses. The variability endogenous to black-skinned population(s) and to the world/reality thereof further amplifies skin complexity. The requirement for skin color researchers and indeed for any researcher to produce research representative of and consistent with the researched and with related world cannot be dispensed with if (skin) researchers want to avoid endogeneity shortcomings. A reformulation of Gloger theory, if any, will have to rephrase if not replace Gloger arguments exposed above. In place of a closed-in and locked-up theory, Gloger himself left a theory that is open to newer findings and reflections. Gloger-postulated theory, Gloger stated arguments, and Rensch-Gloger theory can help researchers remove the misunderstandings about black skin.