NotPoliticallyCorrect

Home » Posts tagged 'Skin Color'

Tag Archives: Skin Color

Advertisements

Black and White Skin

1750 words

Skin color is the first thing you see when you see someone. Skin color has many uses, and the color of one’s skin can give you a general idea of the type of climate one’s ancestors evolved in. The lighter one’s skin is may tell you that their ancestors evolved in low UVB radiation, whereas the darker one’s skin is may tell you that their ancestors evolved in high UVB places. So this tells us that as migration occurred out of Africa, skin needed to lighten in order to synthesize vitamin D in low UVB climes. Note that I won’t make any claims about any skin color being an adaptation to any climate; I will just state that there is a strong association between UVB and skin color—the higher the UVB the darker the skin and the lower the UVB the lighter the skin.

The skin comprises about 16 percent of the human body, making it the body’s largest organ (D’Orazio et al, 2013). There are two layers to the skin, the dermis and epidermis. The outermost layer of skin—the epidermis—is the point of contact with the environment. So since this is the case, then the number of UVB rays in any given environment will dictate the color of one’s skin—in an ancestral manner.

So the most important factor in skin color is melanin, which is produced by melanocytes, but it accumulates in the keratinocytes of the stratum basale (the deepest layer of the five layers of the epidermis) and the stratum spinosum (the layer between the stratum granulosum and the stratum basale). Two forms of melanin exist: eumelanin (which is brownish black) and pheomelanin (which is reddish-yellow and contains sulfur).

In his textbook Anatomy and Physiology: The Unity of Form and Function, professor Ken Saladin writes:

People of different skin colors have essentially the same number of melanocytes, but in dark-skinned people, the melanocytes produce greater quantities of melanin, the melanin granules in the keratanocytes are more spread out than tightly clumped, and the melanin breaks down more slowly. Thus, melanized cells may be seen throughout the epidermis, from stratum basale to stratum corneum. In light-skinned people, the melanin is clumped near the keratinocyte nucleus, so it imparts less color to the cells. It also breaks down more rapidly, so little of it is seen beyond the stratum basale, if even there.

The amount of melanin in the skin also varies with exposure to ultraviolet (UV) rays of sunlight, which stimulates melanin synthesis and darken the skin. A sun-tan fades as melanin is degraded in older keratinocytes and as the keratinocytes migrate to the surface and exfoliate. (Saladin, 2010: 194)

Skin color is one of the most significant factors involved in colonizing a certain, new, area where the skin color the group has is not conducive to life in that clime. So, when the out of Africa migration occurred, skin color needed to lighten as to better confer survival in the new, colder climes. Though, there is an anomaly: Arctic peoples. Why is their skin dark—at least relative to other peoples who live or have lived in colder climates?

Think about life in the Arctic. It is pretty much all white. Food is scarce, and they eat a lot of animal fat and protein. Now, think about the ice. The ice reflects UV rays onto the skin of the Arctic people, making it not as light as, say, Europeans and East Asians.

A term I’ve heard a lot over the years is “Black don’t crack”, speaking to the fact that a lot of black people look young, even into old age. What, if any, is the physiologic reason behind this? For instance, Vashi, Maymone, and Kundu (2016) write:

Individuals with darker skin are overall thought to have firmer and smoother skin than individuals with lighter skin of the same age

Rawlings (2006) states that “Caucasians have an earlier onset and greater skin wrinkling and sagging signs than other skin types and in general increased pigmentary problems are seen in skin of colour although one large study reported that East Asians living in the U.S.A. had the least pigment spots.” Blacks have more corneosome layers than whites (21.8 cell layers compared to 16.7 cell layers). There is no difference in skin thickness between whites and blacks, so black skin is thought to be more compact with greater intercellular cohesion (see also La Ruche and Cesarini, 1992). Take transepidermal water loss (TEWL)—the total amount of water vapor lost through the skin and other appendages through non-sweating conditions. Since the Asian corneum is thinner, it takes fewer tape strippings to decrease TEWL compared to blacks who take more tape strippings, while whites are in the middle. (Though some studies note no difference).

Rawlins (2006: 85) notes that Sugino, Imokawa, and Maibach (1993) state that TEWL is greater in the order of Blacks > Caucasians > Hispanics > Asians.

So why does it seem that blacks, on average, age less than whites in the fact? I can think of one main thing: Their darker skin protects them from the effects of photoaging due to the melanocytes their skin produces. The opposite holds for whites—white skin produces fewer melanocytes and therefore is less protected against UV rays from the sun. Therefore lighter ethnic groups are more likely to have damaged skin compared to darker ethnic groups, and the main driver of this is the number of melanocytes produced by the skin. Rawlings (2006: 87) even writes that “Overall I would expect less signs of aging, i.e. maintenance of skin elasticity in darker skinned individuals [Negroids are reported to have an intrinsic sun protection factor (SPF) value of approximately 13].

Rawlings also writes (pg 89):

In African Americans photoaging appears primarily in lighter complexioned individuals and usually does not appear until the late fifth or sixth decade of life.

There is another factor when it comes to skin: sweat glans. I have covered in the past the fact that Asians have fewer apocrine sweat glands than whites and blacks, while blacks produce more chloride in their sweat compared to whites. Prokop-Prigge et al (2017) state “that an individual’s ethnicity has a significant impact on human axillary odor production.” Blacks also have around 70 percent more lipids in their hair, while having larger sebaceous glands than whites.

So skin color dictates numerous changes in the skin which are associated with aging. Skin aging is associated with lighter-skin, whereas hyperpigmentation is associated with darker skin. Asians have lower TEWL, highest water content, and highest skin color lipid levels while the opposite is seen for blacks. Blacks have greater gland pore size, and increased apocrine and apoeccrine sweat glands along with greater sebum excretion. White skin has an earlier onset of aging, skin wrinkling and loss of elasticity. So there are differences in ethnic skin color and structure and function, and this causes the differences we notice between ethnies and how they age.

Campiche et al (2019) write:

There is differential manifestation of aging signs in different ethnic groups.

[…]

Our results show that Africans from the African continent show delayed signs of aging compared to Caucasians.

They found no differences in forehead wrinkles between Caucasians and Africans, though there was a difference in depth of forehead wrinkles. Blacks showed less advanced crow’s feet than whites, while also having less depth. There were no differences in mouth frown lines with the exception of depth and wrinkle surface and volume parameter, of which there was an increase in Caucasian subjects compared to African subjects. Though when it comes to the length, surface and vertical lines in African subjects they showed more advanced aging but there was no difference in depth between the races. Caucasians had bigger nasiolabial folds (smile or laugh lines) than Africans, regarding length, surface, depth and volume. Africans had deeper pores than Caucasians. Africans had a greater homogeneity than Caucasians when it came to skin color. (Note that the cohorts came from France and Mauritius.)

Campiche et al (2019: 12) write:

This is also in line with the fact that photoaging in African Americans does not appear until the late fifth or sixth decade of life.22 This may explain why aging in our Black African cohort from Mauritius is less pronounced than in the Caucasian cohort although the Black African cohort is older.

[…]

The difference in age between our Caucasian and Black African cohorts (median age 46 years vs 56 years) could bring into question the comparisons of the two cohorts. Nevertheless, we mostly found that Caucasians displayed more severe signs of aging than Black Africans which is in line with the common understanding that the onset of aging in fair skin starts earlier than in darkly pigmented skin and that there were differences in the appearance of lip lines and facial pores.

So differences between the two ethnic groups come down to facial site, and measurement parameter. This study further buttresses the point that, at least when it comes to certain ethnic groups, whites age faster than blacks—even when the whites are younger than blacks (46 compared to 56 years, respectively).

When it comes to skin color and desirability, though, we see something else: light skin being prized, whereas dark skin is shunned. Jablonski (2010: 188) writes:

As we have seen, for much of recent history and around the world, pale skin has been prized to such a degree that people have been willing to risk illness and disfugurement to obtain it.

[and also on pg 177]

Preferences for light skin have arisen independently in many cultures, and they have been reinforced when different “cultures of lightness” have come into contact. Because having lighter skin has often been associated with higher social status, success, and happiness, people over the ages have sought to become lighter by various means.

I won’t ruminate on the causes of this, I just wanted to make a note of it at the end of this piece on black and white skin color.

In sum, there are many interesting differences between black and white—and even Asian—skin. Better understanding of these kinds of differences will lead to better skin care for all races, and dermatologists can then use that information to give better case based on race/ethnicity/skin color to a certain individual. We know what causes differences in skin color between individuals and groups—melanocytes. We also know that skin color and UVB radiation are strongly related. We know that there are numerous differences in skin biology when comparing different peoples whose ancestors have evolved in different climates. So understanding these differences can and will lead to better healthcare for all populations.

Advertisements

Nina Jablonski on Race

1550 words

Nina Jablonski’s work on vitamin D and the implications that lighter skin had not only on our evolution but our health are extremely important for understanding how we evolved after the out of Africa migration. However, Jablonski then takes what she has written about skin color over the past few decades and concludes that race doesn’t exist. Jablonski believes that the term “race” should be discontinued from our lexicon, but as most may know, the term “race” does not need to disappear from our lexicon. (Watch her TED Talk Skin Color is an Illusion.)

In 2014, Nina Jablonski stated that the term “race” was ready for scientific retirement. In the article—and her book (Jablonski, 2012: chapters 9 and 10)—she states that race was a “vague and slippery concept”, eschewing the views of Kant and Hume as “racist”. She talks about how Kant was really one of the first people to recognize and categorize groups of people as “races”, stating that skin color, hair type, skull type etc—along with differing mores, aptitudes, and capacity for civilization—arranged in a hierarchical manner with Europeans at the top. A climatic theory was held, which stated that the original humans were light and became darker since “the transformation from light to dark was a form of degeneration, a departure from the norm” (Jablonski, 2012: 143).

She then discusses how, in Biblical history, skin color was meaningful, meaningful because it was believed that darker-skinned races were descendants of Ham:

And the sons of Noah, that went forth of the ark, were Shem, and Ham, and Japheth: and Ham is the father of Canaan. These are the three sons of Noah: and of them was the whole earth overspread. And Noah began to be an husbandman, and he planted a vineyard: And he drank of the wine, and was drunken; and he was uncovered within his tent. And Ham, the father of Canaan, saw the nakedness of his father, and told his two brethren without. And Shem and Japheth took a garment, and laid it upon both their shoulders, and went backward, and covered the nakedness of their father; and their faces were backward, and they saw not their father’s nakedness. And Noah awoke from his wine, and knew what his younger son had done unto him. And he said, Cursed be Canaan; a servant of servants shall he be unto his brethren. And he said, Blessed be the Lord God of Shem; and Canaan shall be his servant. (Genesis, 9: 18-26)

So Noah’s three sons—Ham, Japheth and Shem—were seen to be the three modern-day races of man—Africans, Europeans, and Asians, respectively. The term “servant of servants” was taken to mean that the descendants of Ham would serve the descendants of Shem and Japheth. This, according to those who believed the authority of the Bible, was enough to justify chattel slavery.

Jablonski—in an interview with the magazine Nautilus—stated that there “are no clean breaks between human populations. Individuals have different groups of genes” and that “Only a tiny fraction of alleles, and a small fraction of allelic combinations, is restricted to a single geographic region, and even less to a single population” which “is why attempts to identify races in humans have failed.” She commits the continuum fallacy, and the argument form is thus: “One extreme is X, at another is Y. There is no definable point where X becomes Y. Therefore, there is no difference between X and Y.” This has also been called the “Argument of the Beard”: at what point does a man not become clean shaven?

The use of the continuum fallacy, that there “are no clean breaks between human populations” shows how far the “race is a social construct” line has come (it is, but that race is a social construct does not also mean that it cannot also be a significant biological reality). The continuum fallacy is one of the most-used fallacies by those who deny race. Though, those who use the continuum fallacy are only attempting to argue that the claim is “too vague” because it is not as precise as they would like it to be. It does not matter that there “are no clean breaks between human populations“; what matters is that patterns of visible physical features correspond to geographic ancestry, and this is what we find.

Her second problem arises when she says that “Only a tiny fraction of alleles, and a small fraction od allelic combinations, is restricted to a single geographic region, and even less to s single population“. That there are no “race genes” or “genes for race” does not mean that race does not exist as a biological reality; these rigid “either this or that” definitions that some people have for race, such as race-specific genes are strawmen: people who believe that race is a significant biological reality do not believe in race-specific genes. That there are no race-specific genes does not mean that race doesn’t exist, as we know that genes are expressed differently in different races.

Finally, she claims that this “is why attempts to identify races in humans have failed“, though these attempts have not failed, of course. So-called races are distinguished by patterns of visible physical features; these patterns are observed between real, existing groups; these real existing groups that share these patterns of visible physical features satisfy the requisites of minimalist race; therefore race exists. Of course, Jablonski has reservations about acknowledging the reality of race due to how the transatlantic slave trade was promogulated through so-called differences that stemmed from Noah and Ham’s curse, but I fail to see why she would discard the argument just provided for the existence of race since differences in mores, intelligence, physical and mental abilities, are not discussed in the argument. ONLY the observable differences between populations are observed, with no value-judgment put onto each race, such as having lower “intelligence” or differing mores compared to another race.

She also states, in an interview with the New York Times, that skin color is not about race, “it’s about sun and how close our ancestors lived to the Equator. Skin color is what regulates our body’s reaction to the sun and its rays. … That shows that color is not a permanent trait.” That the differences in skin color observed in human populations can change over time does not mean that skin color “is not about race” as Jablonski claims. Skin color is one physical trait to delineate races, along with hair type, physiognomy, and anatomy, that groups peoples into groups we call “races”. This is not a good argument against the existence of race; of course anatomy, physiology, and physiognomy can change over time: but this does not mean that race does not exist!

Michael Hardimon’s race concepts (Hardimon, 2017) show that one does not need to believe that races differ in “intelligence”, mores, etc to believe in the existence of race. The concept takes everything from the racialist concept and “minimizes it”, taking the aspect of visible differences in physical features, while leaving the so-called mental differences (“intelligence”, mores) alone. This is enough to recognize that race exists and, as Jablonski has noted for decades in her career, being displaced from the environment where your skin color evolved causes an environmental mismatch which then—in the case of black Americans—may lead to vitamin D deficiency. This is one significant aspect that shows that race has an impact on health policy.

The minimalist concept of race is “deflationary” in that it does not discuss what we “can’t see” with our own eyes; it only discusses physical traits which should be enough for Jablonski to say that race is real and exists as a biological reality. Combined with the known health effects of, for instance, living in differing climates with differing amounts of UV radiation that is not “for” your skin color has further consequences and is why, in some cases, race-based medicine should stick around (though I am aware that, first and foremost, the individual matters first in a medical context, racial membership is secondary).

In sum, Jablonski refers to old and outdated individuals when speaking about the biological reality of race. She does a good job chronicling how and why the concept of race arose, especially through Biblical history and the curse of Ham. However, she takes it too far and claims that race does not exist, nor is it a significant biological reality since there are no “race-specific genes” (also remember that you do not need genes to delineate race, using differences in physical traits and then correlating them to geography is sufficient) and there “are no clean breaks between human populations“. These fallacies aside, it is possible, as I have noted before, to denote racial classifications sans the use of “intelligence” or “mores” in the concept. Skin color is just one of many observable traits that differ by geography that make the basis for separating groups on the basis of race.

The minimalist race concept from Hardimon is non-hierarchical: meaning that it doesn’t discuss anything that would put races in a hierarchy like the racialist concept does (with mores and “intelligence”). If anything, this strictly physical definition of races (and the simple argument for it) should be enough to sway race-deniers to become race-believers.

It Makes Logical Sense for Santa Claus to Be a White Man

1100 words

Of course, with Christmas just around the corner, it is getting attacked like it does every year. The song ‘White Christmasgot attacked a few years back (a personal favorite of mine during the Holiday season). I recall the attacks on the song a few years back, I used to live in the NYC metro area and I remember very clearly that the song would get strongly attacked by ‘PoCs’ because it was ‘racist’ because it was talking about a ‘white Christmas’. Well, there has been even more crazy attacks against Christmas and this time, it’s against Santa!

This attack on ol’ Saint Nick leads to him having homosexual relations with a black man, which brings me to the point of this article: Santa is being attacked now for being white and it’s clear that people don’t know a thing about skin color and cold adaptations when it comes to skin color. Of course, people choose ideology before science. It’s ridiculous that I have to write an article like this but in #2017 I’m not too surprised.

A writer for Slate, Aisha Harris, published an article back in 2013 titled “Santa Claus Should Not Be a White Man Anymore: It’s time to give St. Nick his long overdue makeover“. In the article, Harris states that she saw two Santas while growing up: one black and the other white. Her father stated that Santa came in every color. She states that decades later America is “less and less white” and that “a melanin-deficient Santa remains the default in commercials, mall castings, and movies”. The author goes on to state that we should replace white Santa with a penguin, and call it penguin Claus. But penguins live in the South Pole, not the North Pole, so the author’s contention here, again, doesn’t make sense.

Megyn Kelly discussed this article where she brings up good points that just because white Santa makes you uncomfortable that doesn’t mean that it has to change. She’s right. Your feelings don’t really matter to a long-standing tradition; if you want to make Santa black, that’s your right to do so in your household just know that 1) it doesn’t make logical sense and 2) you can’t impose your will on what you believe Christmas should or should not be like based on your feelings. I know the world is beginning to work like that today (changes based on people’s feelings), but people need to really grow up and accept certain things, especially if these things are sound and logical.

Talking about illogical statements, Andy Ostroy in HuffPo (low-hanging fruit, I know) writes an article in response to Megyn’s small tirade and states: “Yes it does, Megyn. Just because white people have concluded that Santa is white doesn’t make it right, a fact or a status that’s immune from change. It doesn’t matter what he’s ‘always been.’ I’m sure prior to 1865 there were a lot of white folks who said about slaves, “but they’ve always been slaves!”” Here’s another guy who doesn’t logic. Sure, it ‘may not matter what he’s ‘always been”, howeber if you’re looking for logical consistency with what we know about human skin variation then you will see that, even though ‘white people have concluded that Santa is white’ literally makes logical sense due to how human skin variation has evolved. We have scientific evidence for that, as you say in your piece in regard to one of Megyn’s contributors saying that it wouldn’t work because penguins live in the South Pole.

So, sorry Andy Ostroy, but Santa Claus is white.

However, you have articles like this one from The Atlantic titled “Megyn Kelly Assures Everyone That Santa Is White Even Though Santa Does Not Exist“, well I’m here to tell you that I assure everyone that Santa is white even though he doesn’t exist because logical deductions can be made based on where he lives.

This article talks about where to find black Santas that are ‘peppered’ all over the country (do you think the author of this article realizes what he wrote there?). Even former NBA all-star Baron Davis states that “his eyes see no color”. A man was teaching that “Santa comes in all colors“. People need to be logical when talking about skin color and Santa Claus, because by making ol’ St. Nick have dark skin, they’re really showing absolutely no logical thought at all.

In my article The Evolution of Human Skin Variation, I discussed how and why those people who migrated out of Africa evolved lighter skin due to migrating into high latitudes: vitamin D production. People with lighter skin can synthesize the steroid whereas people with darker skin, for instance, get diseases like rickets from not having much vitamin D. Though, logical thought such as this escapes people when they assert that Santa should be black or a ‘PoC’, they show that they do not have any knowledge of latitude, UV rays and skin color which evolves due to the intensity of UV rays.

Santa is based on St. Nicholas, a man who lived during the third century from the village Patara, which is now modern-day Turkey. This is the basis for the Santa Claus we all know and love today, and he was a white man. Santa Claus has his origins being brought to the New World by the first European settlers. Others have claimed that Santa borrows ideas from the Germanic god Wodan and other Pagan figures. Whatever the case may be, we have a few lines of evidence that he is white: 1) the man he was based off was European; 2) he was based on European legends and gods; and perhaps most importantly, 3) he lives at the damn North Pole where it makes sense to be white and have light skin to better produce vitamin D! This attack on Santa being white literally makes no sense at all.

Santa being white is logical, if a human lives at the North Pole for an extended amount of time, he will definitely be a white man due to how skin evolves in those latitudes. If you want to create a black Santa, that’s you’re right to do so. People really should stop letting their shitty ideologies permeate into everything we as a society do in America. The people who push a black Santa should know that if this version of Santa lives at the North Pole he’d quickly die due to lack of vitamin D production. Can’t let logic get in the way of a feel-good story though! Logic and reason is a white male construct anyway!

The Evolution of Human Skin Variation

4050 words

Human skin variation comes down to how much UV radiation a population is exposed to. Over time, this leads to changes in genetic expression. If that new genotype is advantageous in that environment, it will get selected for. To see how human skin variation evolved, we must first look to chimpanzees since they are our closest relative.

The evolution of black skin

Humans and chimps diverged around 6-12 mya. Since we share 99.8 percent of our genome with them, it’s safe to say that when we diverged, we had pale skin and a lot of fur on our bodies (Jablonski and Chaplin, 2000). After we lost the fur on our bodies, we were better able to thermoregulate, which then primed Erectus for running (Liberman, 2015). The advent of fur loss coincides with the appearance of sweat glands in Erectus, which would have been paramount for persistence hunting in the African savanna 1.9 mya, when a modern pelvis—and most likely a modern gluteus maximus—emerged in the fossil record (Lieberman et al, 2006). This sets the stage for one of the most important factors in regards to the ability to persistence hunt—mainly, the evolution of dark skin to protect against high amounts of UV radiation.

After Erectus lost his fur, the unforgiving UV radiation beamed down on him. Selection would have then occurred for darker skin, as darker skin protects against UV radiation. Dark skin in our genus also evolved between 1 and 2 mya. We know this since the melanocortin 1 receptor promoting black skin arose 1-2 mya, right around the time Erectus appeared and lost its fur (Lieberman, 2015).

However, other researchers reject Greaves’ explanation for skin cancer being a driver for skin color (Jablonksi and Chaplin, 2014). They cite Blum (1961) showing that skin cancer is acquired too late in life to have any kind of effect on reproductive success. Skin cancer rates in black Americans are low compared to white Americans in a survey from 1977-8 showing that 30 percent of blacks had basal cell carcinoma while 80 percent of whites did (Moon et al, 1987). This is some good evidence for Greaves’ hypothesis; that blacks have less of a rate of one type of skin cancer shows its adaptive benefits. Black skin evolved due to the need for protection from high levels of UVB radiation and skin cancers.

Highly melanized skin also protects against folate destruction (Jablonksi and Chaplin, 2000). As populations move away from high UV areas, the selective constraint to maintain high levels of folate by blocking high levels of UV is removed, whereas selection for less melanin prevails to allow enough radiation to synthesize vitamin D. Black skin is important near the equator to protect against folate deficiency. (Also see Nina Jablonski’s Ted Talk Skin color is an illusion.)

The evolution of white skin

The evolution of white skin, of course, is much debated as well. Theories range from sexual selection, to diet, to less UV radiation. All three have great explanatory power, and I believe that all of them did drive the evolution of white skin, but with different percentages.

The main driver of white skin is living in colder environments with fewer UV rays. The body needs to synthesize vitamin D, so the only way this would occur in areas with low UV rays.

White skin is a recent trait in humans, appearing only 8kya. A myriad of theories have been proposed to explain this, from sexual selection (Frost, 2007), which include better vitamin D synthesis to ensure more calcium for pregnancy and lactation (which would then benefit the intelligence of the babes) (Jablonski and Chaplin, 2000); others see light skin as the beginnings of more childlike traits such as smoother skin, a higher pitched voice and a more childlike face which would then facilitate less aggressiveness in men and more provisioning (Guthrie, 1970; from Frost, 2007); finally, van den Berghe and Frost (1986) proposed that selection for white skin involved unconscious selection by men for lighter-skinned women which is used “as a measure of hormonal status and thus childbearing potential” (Frost, 2007). The three aforementioned hypotheses have sexual selection for lighter skin as a proximate cause, but the ultimate cause is something completely different.

The hypothesis that white skin evolved to better facilitate vitamin D synthesis to ensure more calcium for pregnancy and lactation makes the most sense. Darker-skinned individuals have a myriad of health problems outside of their ancestral climate, one of which is higher rates of prostate cancer due to lack of vitamin D. If darker skin is a problem in cooler climates with fewer UV rays, then lighter skin, since it ensures better vitamin D synthesis, will be selected for. White skin ensures better and more vitamin D absorption in colder climates with fewer UV rays, therefore, the ultimate cause of the evolution of white skin is a lack of sunlight and therefore fewer UV rays. This is because white skin absorbs more UV rays which is better vitamin D synthesis.

Peter Frost believes that Europeans became white 11,000 years ago. However, as shown above, white skin evolved around 8kya. Further, contrary to popular belief, Europeans did not gain the alleles for white skin from Neanderthals (Beleza et al, 2012). European populations did not lose their dark skin immediately upon entering Europe—and Neanderthal interbreeding didn’t immediately confer the advantageous white skin alleles. There was interbreeding between AMH and Neanderthals (Sankararaman et al, 2014). So if interbreeding with Neanderthals didn’t infer white skin to proto-Europeans, then what did?

A few alleles spreading into Europe that only reached fixation a few thousand years ago. White skin is a relatively recent trait in Man (Beleza et al, 2012). People assume that white skin has been around for a long time, and that Europeans 40,000 ya are the ancestors of Europeans alive today. That, however, is not true. Modern-day European genetic history began about 6,500 ya. That is when the modern-day European phenotype arose—along with white skin.

Furthermore, Eurasians were still a single breeding population 40 kya, and only diverged recently, about 25,000 to 40,000 ya (Tateno et al, 2014). The alleles that code for light skin evolved after the Eurasian divergence. Polymorphisms in the genes ASIP and OCA2 may code for dark and light skin all throughout the world, whereas SLC24A5, MATP, and TYR have a predominant role in the evolution of light skin in Europeans but not East Asians, which suggests recent convergent evolution of a lighter pigmentation phenotype in European and East Asian populations (Norton et al, 2006). Since SLC24A5, MATP, and TYR are absent in East Asian populations, then that means that East Asians evolved light skin through completely different mechanisms than Europeans. So after the divergence of East Asians and Europeans from a single breeding population 25-40kya, there was convergent evolution for light pigmentation in both populations with the same selection pressure (low UV).

Some populations, such as Arctic peoples, don’t have the skin color one would predict they should have based on their ancestral environment. However, their diets are high in shellfish which is high in vitamin D, which means they can afford to remain darker-skinned in low UV areas. UV rays reflect off of the snow and ice in the summer and their dark skin protects them from UV light.

Black-white differences in UV absorption

If white skin evolved to better synthesize vitamin D with fewer (and less intense) UV rays, then those with blacker skin would need to spend a longer time in UV light to synthesize the same amount of vitamin D. Skin pigmentation, however, is negatively correlated with vitamin D synthesis (Libon, Cavalier, and Nikkels, 2013). Black skin is less capable of vitamin D synthesis. Furthermore, blacks’ skin color leads to an evolutionary environmental mismatch. Black skin in low UV areas is correlated with rickets (Holick, 2006), higher rates of prostate cancer due to lower levels of vitamin D (Gupta et al, 2009; vitamin D supplements may also keep low-grade prostate cancer at bay).

Libon, Cavalier, and Nikkels, (2013) looked at a few different phototypes (skin colors) of black and white subjects. The phototypes they looked at were II (n=19), III (n=1), and VI (n-11; whites and blacks respectively). Phototypes are shown in the image below.

skin-type-chart

fitzpatrick-color-chart

To avoid the influence of solar UVB exposure, this study was conducted in February. On day 0, both the black and white subjects were vitamin D deficient. The median levels of vitamin D in the white subjects was 11.9 ng/ml whereas for the black subjects it was 8.6 ng/ml—a non-statistically significant difference. On day two, however, concentrations of vitamin D in the blood rose from 11.9 to 13.3 ng/ml—a statistically significant difference. For the black cohort, however, there was no statistically significant difference in vitamin D levels. On day 6, levels in the white subjects rose from 11.6 to 14.3 ng/ml whereas for the black subjects it was 8.6 to 9.57 ng/ml. At the end of day 6, there was a statistically significant difference in circulating vitamin D levels between the white and black subjects (14.3 ng/ml compared to 9.57 ng/ml).

Different phototypes absorb different amounts of UV rays and, therefore, peoples with different skin color absorb different levels of vitamin D. Lighter-skinned people absorb more UV rays than darker-skinned people, showing that white skin’s primary cause is to synthesize vitamin D.

UVB exposure increases vitamin D production in white skin, but not in black skin. Pigmented skin, on the other hand, hinders the transformation of 7-dehydrocholesterol to vitamin D. This is why blacks have higher rates of prostate cancer—they are outside of their ancestral environment and what comes with being outside of one’s ancestral environment are evolutionary mismatches. We have now spread throughout the world, and people with certain skin colors may not be adapted for their current environment. This is what we see with black Americans as well as white Americans who spend too much time in climes that are not ancestral to them. Nevertheless, different-colored skin does synthesize vitamin D differently, and knowledge of this will increase the quality of life for everyone.

Even the great Darwin wrote about differences in human skin color. He didn’t touch human evolution in On the Origin of Species (Darwin, 1859), but he did in his book Descent of Man (Darwin, 1871). Darwin talks about the effects of climate on skin color and hair, writing:

It was formerly thought that the colour of the skin and the character of the hair were determined by light or heat; and although it can hardly be denied that some effect is thus produced, almost all observers now agree that the effect has been very small, even after exposure during many ages. (Darwin, 1871: 115-116)

Darwin, of course, championed sexual selection as the cause for human skin variation (Darwin, 1871: 241-250). Jared Diamond has the same view, believing that natural selection couldn’t account for hair loss, black skin and white skin weren’t products of natural selection, but female mate preference and sexual selection (Greaves, 2014).

Parental selection for white skin 

Judith Rich Harris, author of the book The Nurture Assumption: Why Kids Turn Out the Way They Do (Harris, 2009), posits another hypothesis for the evolution of light skin for those living in northern latitudes—parental selection. This hypothesis may be controversial to some, as it states that dark skin is not beautiful and that white skin is.

Harris posits that selection for lighter skin was driven by sexual selection, but states that parental selection for lighter skin further helped the fixation of the alleles for white skin in northern populations. Neanderthals were a furry population, as they had no clothes, so, logic dictates that if they didn’t have clothes then they must have had some sort of protection against the cold Ice Age climate, therefore they must have had fur.

Harris states that since lighter skin is seen as more beautiful than darker skin, then if a woman birthed a darker/furrier babe than the mother would have committed infanticide. Women who birth at younger ages are more likely to commit infanticide, as they still have about twenty years to birth a babe. On the other hand, infanticide rates for mothers decrease as she gets older—because it’s harder to have children the older you get.

Harris states that Erectus may have been furry up until 2 mya, however, as I’ve shown, Erectus was furless and had the ability to thermoregulate—something that a hairy hominin was not able to do (Lieberman, 2015).

There is a preference for lighter-skinned females all throughout the world, in Africa (Coetzee et al, 2012); China and India (Naidoo et al, 2016; Dixson et al, 2007); and Latin America and the Philipines (Kiang and Takeuchi, 2009). Light skin is seen as attractive all throughout the world. Thus, since light skin allows better synthesize of vitamin D in colder climes with fewer UV rays, then there would have been a myriad of selective pressures to push that along—parental selection for lighter-skinned babes being one of them. This isn’t talked about often, but infanticide and rape have both driven our evolution (more on both in the future).

Harris’ parental selection hypothesis is plausible, and she does use the right dates for fur loss which coincides with the endurance running of Erectus and how he was able to thermoregulate body heat due to lack of fur and more sweat glands. This is when black skin began to evolve. So with migration into more northerly climes,  lighter-skinned people would have more of an advantage than darker-skinned people. Infanticide is practiced all over the world, and is caused—partly—by a mother’s unconscious preferences.

Skin color and attractiveness

Lighter skin is seen as attractive all throughout the world. College-aged black women find lighter skin more attractive (Stephens and Thomas, 2012). It is no surprise that due to this, a lot of black women lighten their skin with chemicals.

In a sample of black men, lighter-skinned blacks were more likely to perceive discrimination than their darker-skinned counterparts (Uzogara et al, 2014). Further, in appraising skin color’s effect on in-group discrimination, medium-skinned black men perceived less discrimination than lighter- and darker-skinned black men. Lastly—as is the case with most studies—this effect was particularly pronounced for those in lower SES brackets. Speaking of SES, lighter-skinned blacks with higher income had lower blood pressure than darker-skinned blacks with higher income (Sweet et al, 2007). The authors conclude that a variety of psychosocial stress due to discrimination must be part of the reason why darker-skinned blacks with a high SES have worse blood pressure—but I think there is something else at work here. Darker skin on its own is associated with high blood pressure (Mosley et al, 2000). I don’t deny that (perceived) discrimination can and does heighten blood pressure—but the first thing that needs to be looked at is skin color.

Lighter-skinned women are seen as more attractive (Stephen et al, 2009). This is because it signals fertility, femininity, and youth. One more important thing it signals is the ability to carry a healthy child to term since lighter skin in women is associated with better vitamin D synthesis which is important for a growing babe.

Skin color and intelligence

There is a high negative correlation between skin color and intelligence, about –.92 (Templer and Arikawa, 2006). They used the data from Lynn and Vanhanen’s 2002 book IQ and the Wealth of Nations and found that there was an extremely strong negative correlation between skin color and IQ. However, data wasn’t collected for all countries tested and for half of the countries the IQs were ‘estimated’ from other surrounding countries’ IQs.

Jensen (2006) states that the main limitation in the study design of Arikawa and Templer (2006) is that “correlations obtained from this type of analysis are completely non-informative regarding any causal or functional connection between individual differences in skin pigmentation and individual differences in IQ, nor are they informative regarding the causal basis of the correlation, e.g., simple genetic association due to cross-assortative mating for skin color and IQ versus a pleiotropic correlation in which both of the phenotypically distinct but correlated traits are manifested by one and the same gene.”

Lynn (2002) purported to find a correlation of .14 in a representative sample of American blacks (n=430), concluding that the proportion of European genes in African Americans dictates how intelligent that individual black is. However, Hill (2002) showed that when controlling for childhood environmental factors such as SES, the correlation disappears and therefore, a genetic causality cannot be inferred from the data that Lynn (2002) used.

Since Lynn found a .14 correlation between skin color and IQ in black Americans, that means that only .0196 percent of the variation in IQ within black American adults can be explained by skin color. This is hardly anything to look at and keep in mind when thinking about racial differences in IQ.

However, other people have different ideas. Others may say that since animal studies find that lighter animals are less sexually active, are less aggressive, have a larger body mass, and greater stress resistance. So since this is seen in over 40 species of vertebrate, some fish species, and over 30 bird species (Rushton and Templer, 2012) that means that it should be a good predictor for human populations. Except it isn’t.

Razib Khan states:

we know the genetic architecture of pigmentation. that is, we know all the genes (~10, usually less than 6 in pairwise between population comparisons). skin color varies via a small number of large effect trait loci. in contrast, I.Q. varies by a huge number of small effect loci. so logically the correlation is obviously just a correlation. to give you an example, SLC45A2 explains 25-40% of the variance between africans and europeans.

long story short: it’s stupid to keep repeating the correlation between skin color and I.Q. as if it’s a novel genetic story. it’s not. i hope don’t have to keep repeating this for too many years.

Finally, variation in skin color between human populations are primarily due to mutations on the genes MC1RTYRMATP (Graf, Hodgson, and Daal, 2005), and SLC24A5 (also see Lopez and Alonso, 2014 for a review of genes that account for skin color) so human populations aren’t “expected to consistently exhibit the associations between melanin-based coloration and the physiological and behavioural traits reported in our study” (Ducrest, Keller, and Roulin, 2008). Talking about just correlations is useless until causality is established (if it ever is).

Conclusion

The evolution of human skin variation is complex and is driven by more than one variable, but some are stronger than others. The evolution of black skin evolved—in part—due to skin cancer after we lost our fur. White skin evolved due to sexual selection (proximate cause) and to better absorb UV rays for vitamin D synthesis in colder climes (the true need for light skin in cold climates). Eurasians split around 40kya, and after this split both evolved light skin pigmentation independently. As I’ve shown, the alleles that code for skin color between blacks and whites don’t account for differences in aggression, nor do they account for differences in IQ. The genes that control skin color (about a dozen) pale in comparison to the genes that control intelligence (thousands of genes with small effects). Some other hypotheses for the evolution of white skin are on par with being as controversial as the hypothesis that skin color and intelligence co-evolved—mainly that mothers would kill darker-skinned babies because they weren’t seen as beautiful as lighter-skinned babies.

The evolution of human skin variation is extremely interesting with many competing hypotheses, however, to draw wild conclusions based on just correlations in regards to human skin color and intelligence and aggression, you’re going to need more evidence than just correlations.

References

Bang KM, Halder RM, White JE, Sampson CC, Wilson J. 1987. Skin cancer in black Americans: A review of 126 cases. J Natl Med Assoc 79:51–58

Beleza, S., Santos, A. M., Mcevoy, B., Alves, I., Martinho, C., Cameron, E., . . . Rocha, J. (2012). The Timing of Pigmentation Lightening in Europeans. Molecular Biology and Evolution,30(1), 24-35. doi:10.1093/molbev/mss207

Blum, H. F. (1961). Does the Melanin Pigment of Human Skin Have Adaptive Value?: An Essay in Human Ecology and the Evolution of Race. The Quarterly Review of Biology,36(1), 50-63. doi:10.1086/403275

Coetzee V, Faerber SJ, Greeff JM, Lefevre CE, Re DE, et al. (2012) African perceptions of female attractiveness. PLOS ONE 7: e48116.

Darwin, C. (1859). On the origin of species by means of natural selection, or, the preservation of favoured races in the struggle for life. London: J. Murray.

Darwin, C. (1871). The descent of man, and selection in relation to sex. London: John Murray, Albemarle Street.

Dixson, B. J., Dixson, A. F., Li, B., & Anderson, M. (2006). Studies of human physique and sexual attractiveness: Sexual preferences of men and women in China. American Journal of Human Biology,19(1), 88-95. doi:10.1002/ajhb.20584

Ducrest, A., Keller, L., & Roulin, A. (2008). Pleiotropy in the melanocortin system, coloration and behavioural syndromes. Trends in Ecology & Evolution,23(9), 502-510. doi:10.1016/j.tree.2008.06.001

Frost, P. (2007). Human skin-color sexual dimorphism: A test of the sexual selection hypothesis. American Journal of Physical Anthropology,133(1), 779-780. doi:10.1002/ajpa.20555

Graf, J., Hodgson, R., & Daal, A. V. (2005). Single nucleotide polymorphisms in theMATP gene are associated with normal human pigmentation variation. Human Mutation,25(3), 278-284. doi:10.1002/humu.20143

Greaves, M. (2014). Was skin cancer a selective force for black pigmentation in early hominin evolution? Proceedings of the Royal Society B: Biological Sciences,281(1781), 20132955-20132955. doi:10.1098/rspb.2013.2955

Gupta, D., Lammersfeld, C. A., Trukova, K., & Lis, C. G. (2009). Vitamin D and prostate cancer risk: a review of the epidemiological literature. Prostate Cancer and Prostatic Diseases,12(3), 215-226. doi:10.1038/pcan.2009.7

Guthrie RD. 1970. Evolution of human threat display organs. Evol Biol 4:257–302.

Harris, J. R. (2006). Parental selection: A third selection process in the evolution of human hairlessness and skin color. Medical Hypotheses,66(6), 1053-1059. doi:10.1016/j.mehy.2006.01.027

Harris, J. R. (2009). The nurture assumption: why children turn out the way they do. New York: Free Press.

Hill, Mark E. 2002. Skin color and intelligence in African Americans: A reanalysis of Lynn’s data. Population and Environment 24, no. 2:209–14

Holick, M. F. (2006). Resurrection of vitamin D deficiency and rickets. Journal of Clinical Investigation,116(8), 2062-2072. doi:10.1172/jci29449

Jablonski, N. G., & Chaplin, G. (2000). The evolution of human skin coloration. Journal of Human Evolution,39(1), 57-106. doi:10.1006/jhev.2000.0403

Jablonski, N. G., & Chaplin, G. (2014). Skin cancer was not a potent selective force in the evolution of protective pigmentation in early hominins. Proceedings of the Royal Society B: Biological Sciences,281(1789), 20140517-20140517. doi:10.1098/rspb.2014.0517

Jensen, A. R. (2006). Comments on correlations of IQ with skin color and geographic–demographic variables. Intelligence,34(2), 128-131. doi:10.1016/j.intell.2005.04.003

Kiang, L., & Takeuchi, D. T. (2009). Phenotypic Bias and Ethnic Identity in Filipino Americans. Social Science Quarterly,90(2), 428-445. doi:10.1111/j.1540-6237.2009.00625.x

Libon, F., Cavalier, E., & Nikkels, A. (2013). Skin Color Is Relevant to Vitamin D Synthesis. Dermatology,227(3), 250-254. doi:10.1159/000354750

Lieberman, D. E. (2015). Human Locomotion and Heat Loss: An Evolutionary Perspective. Comprehensive Physiology, 99-117. doi:10.1002/cphy.c140011

Lieberman, D. E., Raichlen, D. A., Pontzer, H., Bramble, D. M., & Cutright-Smith, E. (2006). The human gluteus maximus and its role in running. Journal of Experimental Biology,209(11), 2143-2155. doi:10.1242/jeb.02255

López, S., & Alonso, S. (2014). Evolution of Skin Pigmentation Differences in Humans. ELS. doi:10.1002/9780470015902.a0021001.pub2

Lynn, R. (2002). Skin color and intelligence in African Americans. Population and Environment, 23, 365–375.

Mosley, J. D., Appel, L. J., Ashour, Z., Coresh, J., Whelton, P. K., & Ibrahim, M. M. (2000). Relationship Between Skin Color and Blood Pressure in Egyptian Adults : Results From the National Hypertension Project. Hypertension,36(2), 296-302. doi:10.1161/01.hyp.36.2.296

Naidoo, L.; Khoza, N.; Dlova, N.C. A fairer face, a fairer tomorrow? A review of skin lighteners. Cosmetics 2016, 3, 33.

Norton, H. L., Kittles, R. A., Parra, E., Mckeigue, P., Mao, X., Cheng, K., . . . Shriver, M. D. (2006). Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians. Molecular Biology and Evolution,24(3), 710-722. doi:10.1093/molbev/msl203

Rushton, J. P., & Templer, D. I. (2012). Do pigmentation and the melanocortin system modulate aggression and sexuality in humans as they do in other animals? Personality and Individual Differences,53(1), 4-8. doi:10.1016/j.paid.2012.02.015

Sankararaman, S., Mallick, S., Dannemann, M., Prüfer, K., Kelso, J., Pääbo, S., . . . Reich, D. (2014). The genomic landscape of Neanderthal ancestry in present-day humans. Nature,507(7492), 354-357. doi:10.1038/nature12961

Stephen, I. D., Smith, M. J., Stirrat, M. R., & Perrett, D. I. (2009). Facial Skin Coloration Affects Perceived Health of Human Faces. International Journal of Primatology,30(6), 845-857. doi:10.1007/s10764-009-9380-z

Stephens, D., & Thomas, T. L. (2012). The Influence of Skin Color on Heterosexual Black College Women’s Dating Beliefs. Journal of Feminist Family Therapy,24(4), 291-315. doi:10.1080/08952833.2012.710815

Sweet, E., Mcdade, T. W., Kiefe, C. I., & Liu, K. (2007). Relationships Between Skin Color, Income, and Blood Pressure Among African Americans in the CARDIA Study. American Journal of Public Health,97(12), 2253-2259. doi:10.2105/ajph.2006.088799

Tateno, Y., Komiyama, T., Katoh, T., Munkhbat, B., Oka, A., Haida, Y., . . . Inoko, H. (2014). Divergence of East Asians and Europeans Estimated Using Male- and Female-Specific Genetic Markers. Genome Biology and Evolution,6(3), 466-473. doi:10.1093/gbe/evu027

Templer, D. I., & Arikawa, H. (2006). Temperature, skin color, per capita income, and IQ: An international perspective. Intelligence,34(2), 121-139. doi:10.1016/j.intell.2005.04.002

Uzogara, E. E., Lee, H., Abdou, C. M., & Jackson, J. S. (2014). A comparison of skin tone discrimination among African American men: 1995 and 2003. Psychology of Men & Masculinity, 15(2), 201–212. http://doi.org/10.1037/a0033479

van den Berghe PL, Frost P. 1986. Skin color preference, sexual dimorphism and sexual selection: a case of gene-culture coevolution? Ethn Racial Stud 9:87–113.