(Adapted from Do pigmentation and the melanocortin system modulate aggression and sexuality in humans as they do in other animals?, by J. Philippe Rushton and Donald I. Templer, Personality and Individual Differences, Volume 53, Issue 1, July 2012, Pages 4–8. [PDF].)
[VDARE.com note: We urge readers to study the citations in the original. Our hyperlinks sometimes differ—if, for example, Professors Rushton and Templer’s source is not available online.]
Pigmentation—coloring—varies greatly across species. In 2008, Anne-Lyse Ducrest, Laurent Keller and Alexandre Roulin, three ecologists at Switzerland’s University of Lucerne published a review article in Trends in Ecology and Evolution [Pleiotropy in the melanocortin system, coloration and behavioral syndromes, September 2008] on the relations between pigmentation, sexuality, and aggression in 45 vertebrate species. They found that darker-colored individuals had higher levels of aggression and sexuality than lighter colored individuals across three species of mammals (African lion, soay sheep, and white-tailed deer), four species of fish (mosquito fish, guppy, green swordtail, and Arctic char), four species of reptiles (asp viper, adder, fence lizard, and spiny lizard), one amphibian species (spadefoot toad), and 36 species of birds.
Ducrest and her co-authors’ explanation: increased levels of melanocortin hormones, which determine coloring, are linked with increased testosterone and other steroids that stimulate aggression and sexuality, among other things.
To test this, Ducrest & Co. experimentally varied melanocortin dosage levels. They found concomitant increases (or decreases) in aggression and sexuality.
They also carried out cross-fostering studies, placing darker and lighter offspring with adoptive parents of the opposite pigmentation. Cross-fostering did not alter the offspring’s coloring or behavior. Male lions with darker manes remained more aggressive and sexually active than those with lighter manes. Darker feathered barn owls continued to have a stronger immune response to stress (another linked phenomenon) than lighter feathered barn owls.
It was the biological, not the adopting, parent that determined both the offspring’s coloration and its behavior.
This link between coloring and behavior has been confirmed in many other species—even tortoises. In Russia, a 40-year-study bred for tameness in silver foxes and found that lightness coincidentally emerged. After 40 years, the selected foxes were as tame and eager to please as domestic dogs—and the dark coat colors originally evolved as camouflage in the wild had been replaced by piebald. (Piebald coats are often seen among domestic animals—in dogs, cats, sheep, donkeys, horses, pigs, goats, mice, and cattle).
Similarly, selecting for tameness over 30 generations of Norway rats caused the proportion of piebald rats to increase rapidly until over 70% had white bellies and about 50% had white feet and ankles—“socks.”
But what about humans? Despite all the evidence on color, aggression, and sexuality in animals, there has been little or no discussion of the relationship in people. Ducrest & Co. even warned that genetic mutations may make human populations not exhibit coloration effects as consistently as other species. But they provided no evidence.
My co-author, Donald I.Templer, formerly Professor of Psychology, Alliant International University [email him], and I were skeptical. After all, if it turned out that the melanocortin system did lead to heightened aggression and sexuality in people, we would have a substantially stronger and more powerful theory to explain aspects of human behavior than before. The hypothesis was worth examining seriously.
Our new paper in Personality and Individual Differences (free download here) reports clear evidence that darker pigmentation is indeed associated with higher levels of aggression and sexuality in humans—just as it is in animals.
We compared people of African descent with those of European and Asian descent. Worldwide— ever since record keeping began—blacks have averaged higher levels of aggression and sexuality than whites and Asians:
Racial differences in sexual behavior parallel those found in crime.
In the Kinsey data, race predicted sexual behavior better than did socioeconomic status. Kinsey’s black sample was college-educated and came from a middle-class background. One of the white samples was non-college educated and had low socioeconomic status. But the middle-class blacks displayed higher levels of sexuality than the working-class whites.
Differences in sexual behavior lead to real-life consequences. For example:
The conventional explanations for these black-white differences focus on cultural deprivation, poverty, slavery, white racism etc. But the analyses presented here (and here, and here, and here) show that genetic factors are also likely involved.
Behavioral genetic analyses, using twin, family, and adoption designs, show that most differences in behavior traits between people are about 50% heritable and are genetically linked. For example, in one study among adolescents, 36 to 49% of the sexual intimacy engaged in by one sibling was predicted by the amount of delinquency engaged in by the other.
Another study found that sexuality and delinquency correlated positively with measures of impulsivity, deceitfulness, and rebelliousness, and negatively with those of parental affection and encouragement of achievement. Moreover, mixed-race (Black-White) adolescents were intermediate in the number of sexual partners they had by comparison to the two parental populations.
There’s other evidence of correlation between color and behavior. A 2006 study by Donald I. Templer and Hiroko Arikawa found a remarkably high correlation of 0.92 between skin color and national IQ across 129 countries and within each of the three continents: -0.86 for Africa; -0.55 for Asia; and -0.63 for Europe. The correlations are negative because darker skin color predicted lower IQ score.
In 2008, Donald I. Templer found that, across 129 countries, skin color correlated with IQ (-0.91), birth rate (0.85), infant mortality (0.71), longevity (-0.84), rate of HIV/AIDS (0.53), and GDP (0.60).
Subsequently, in a 2009 study , Donald Templer and I found skin color also correlated with crime in 113 countries (homicide, 0.34; rape, 0.24: and serious assault, 0.25) as well as with IQ (-0.91), GDP (-0.57), HIV/AIDS (0.56), birth rate (0.87), longevity (-0.85), and infant mortality (0.76). Rates of murder, rape, and serious assault correlated with those of HIV/AIDS (0.48, 0.57, and 0.42, respectively).
Finally, in 2011, Donald Templer and I confirmed the international findings using data from within the 50 U.S. states. Skin color was measured by the percentage of blacks in the state. It correlated with infant mortality (0.41), longevity (-0.66), HIV/AIDS (0.74), birth rate (0.12), murder (0.84), robbery (0.77), assault (0.54), as well as IQ (-0.48) and income (-0.28).
Pigment differences in temperament are also found within human races. A 20 year study by development psychologist Jerome Kagan found that, in kindergarten, blue-eyed children were more likely than brown-eyed children to be shy, wary, and inhibited.
In The Long Shadow of Temperament , Kagan and Snidman reported the shy infants grew to have a dourer temperament in adolescence, whereas the bolder infants were more outgoing in adolescence.
The authors acknowledged that temperament can be modified by experience. But their work showed how far the link between infant temperament and pigmentation could extend over the lifetime.
The correlations between human coloration, aggression, sexuality and IQ may also play a role in the phenomenon of “pigmentocracies”—societies stratified by skin color, with lighter skin denoting higher status. Again, pigmentocracies are conventionally explained by cultural factors such as the legacy of slavery. But our work suggests that the relationship between skin color and behavior may be at work.
Our paper provides only a first approximation of melanin and its correlates. There are complex issues that need to be studied further. Nonetheless, we believe our work points in a direction that could greatly advance knowledge.
J. Philippe Rushton [E-mail him] is a professor of psychology at the University of Western Ontario, London, Ontario, Canada.