Wednesday, March 12, 2014

The Notevolution of Blondness (Ukrainian edition)

An article published in Science on March 10th, 2014, explains how the attractiveness of blond hair pushed human evolution.  The old theory was that, having moved to colder climes where dark pigment wasn’t necessary to protect from the sun, Europeans gradually evolved lighter skin, hair and eye color.  This new theory states that, while that had some impact, there was a big evolutionary jump in the last 6000 to 8000 years, so big that it can only be explained by other forces.  The authors “speculate” that the switch to farming, with less animal consumption and therefore less vitamin D, created an evolutionary pressure for lighter skin to enable more efficient vitamin D production.  But that only explains skin color, not hair.  That, they suggest, is explained by the lust-inducing impact of blondness. Here are the key points of the study (full article here):

… [A] team led by Mark Thomas, an evolutionary geneticist at University College London, extracted DNA from 63 skeletons previously found at archaeological sites in modern-day Ukraine and surrounding areas. The researchers were able to sequence three pigmentation-related genes from 48 of the skeletons, dated between 6500 and 4000 years old … These three genes, like all pigmentation genes, come in numerous variants that lead to different shades of skin, hair, and eye color.

By comparing the variants of these genes in the ancient skeletons with those in 60 modern-day Ukrainians, as well as a larger sample of 246 modern genomes from the surrounding region, the team found that the frequency of variants related to lighter skin and hair, as well as blue eyes, increased significantly between the ancient and modern populations…  Thus, while the prehistoric Ukrainians had apparently evolved relatively lighter skin and hair, and a higher frequency of blue eyes, in the time since their ancestors had left Africa, the data suggested that they were not done evolving. To further test this conclusion, the team performed computer simulations designed to distinguish between natural selection and “genetic drift,” a change in the frequency of genetic variants due just to chance. These tests—which take into account ancient population sizes and the rate at which genetic alterations occur, and can determine whether genetic drift alone can account for the speed of evolutionary changes—showed that the pigmentation genes were still undergoing strong natural selection after 5000 years ago; indeed, the selection pressure was as great as that for other genes known to be very strongly selected in humans, such as those involved in the ability to digest lactose and protection against malaria.

“The signs of selection are indeed persuasive,” Rocha says. By using ancient DNA, he says, the team was able to “provide direct evidence” that “strong positive selection was the likely driver” of the changes in pigmentation profiles…
As for the trend toward lighter colored hair and blue eyes, Thomas and his co-workers suggest that may be due to sexual attraction—what in evolutionary terms is called sexual selection. If so, then the originally rare males or females with light hair and blue eyes might have been attractive to the opposite sex and so had more offspring; this kind of sexual preference for individuals with unusual appearances has been confirmed in other animals, such as guppies. 

I’m not questioning the science.  I’m not questioning the validity of evolution.  It’s the speculations and suggestions that strike me as nothistory. 

Based on two data points, separated in time by 6000 plus years, the scientist have determined the rate of evolutionary change.  All well and good, IF you have an unchanging population, such that evolution is the only factor affecting genetic changes.  But this is the Ukraine, not an isolated island immune from outside forces.  So we need to talk about migration.  Between the 8th and 3rd centuries BCE, the area absorbed both Greek and Iranian populations.  In the 3rd and 4th centuries CE it was the Goths.  The 5th century brought the Huns, the 9th century the Khazars, and the 12th and 13th centuries brought Mongols.  So there’s a lot of change to the gene pool between the early population in the study, who lived in 8500-6000 BCE, and the later, contemporary one.

Did any of these migrants bring in genes for lighter pigmentation?  Well, the Iranians (also referred to as Caucasians) certainly did.  In fact, one of those Iranian groups, the Sarmations, was described this way by a Roman historian: "Nearly all the Alani are men of great stature and beauty, their hair is somewhat yellow, their eyes are frighteningly fierce."  Another option is the Goths, who moved to the Ukraine from Scandinavia.  There is some argument as to whether they originated in Scandinavia or had moved there from some other place.  One thing we do know about human history, however, is that co-location means interbreeding.  If the Goths spent any time at all in Scandinavia, they would have brought a healthy dose of those Northern, sun-deprived, pigment-deficient genes with them. 

With all due respect, I’d like to suggest that the signs for selection are not, in fact, persuasive.  The signs that the scientists can’t tell that their apples are oranges, however, are.

As for the idea that sexual attraction accounts for the increased prevalence of blondness?  Never mind that they can't cite any evidence that, among humans, those considered more attractive at any particular point in history have had more children than those who aren’t.  Let’s just try to remember that human mating behavior is somewhat more complex than that of guppies.

Finally, in homage to Bill Maher, I’d like to suggest a new rule: Scientists aren’t allowed to publish historical interpretations of their work without first consulting with actual historians.