Reports that the Cheddar Man had “dark to black” skin have been blown wildly out of proportion, say the very scientists who studied the ancient specimen’s DNA who is purported to be the ancestor of modern day Britons.
Politically-motivated news stories claimed that the Cheddar Man’s skin was indisputably “dark to black” based on claims by researchers including Susan Walsh at Indiana University-Purdue University Indianapolis, whose study of the DNA was based on a model that attempted to predict eye, hair, and skin pigmentation solely from DNA.
New Scientist (paywalled article) reports that the most recent version of the model was published in May 2017, focusing on 36 spots in 16 genes, all linked to skin color. To test the model, Walsh and her team harvested genetic data from over 1400 people, mainly from Europe and the US, and some from Africa and Papua New Guinea. Using the data, the team “trained” their model on how skin color and the 36 DNA markers are linked, using it to predict if a person was light or dark-skinned with a small margin of error.
Walsh then applied the model to Cheddar Man and concluded that his skin fell between “dark” and “dark to black,” prompting the news stories. The research was first announced by press release to coincide with the release of a TV documentary, and has only now been published on a preprint server, according to New Scientist.
Contrary to reports, Walsh says that her study does not “conclusively demonstrate” Cheddar Man had “dark to black” skin. She says that placing confidence in the DNA analysis would be a mistake, and notes that Cheddar Man’s DNA has degraded over the last 10,000 years since he was buried in a cave in south-east England.
“It’s not a simple statement of ‘this person was dark-skinned’,” said Walsh. “It is his most probable profile, based on current research.”
Stony Brook University’s Brenna Henn says that the science of predicting the skin color of prehistoric people through their genes just isn’t there yet, as the genetics of skin pigmentation are as yet under-researched and more complex than previously thought.
New Scientist reports that Henn and her colleagues published a paper in November 2017 on the very subject, exploring the genetics of skin pigmentation in populations indigenous to southern Africa, which has a wide variety of skin pigmentation—more so than most people realize. Similar research was conducted by a group led by Sarah Tishkoff at the University of Pennsylvania on the skin pigmentation of people indigenous to eastern and southern Africa just weeks before.
“The conclusions were really the same,” Henn said to New Scientist. “Known skin pigmentation genes, discovered primarily in East Asian and European populations, don’t explain the variation in skin pigmentation in African populations. The idea that there are really only about 15 genes underlying skin pigmentation isn’t correct.”
Henn states that there are many other genes that affect skin color, but the exact number remains unknown. Given scientists’ lack of understanding even in living populations today, predicting the skin color of prehistoric people remains a far cry, she says. The results also vary wildly depending on how the model is trained.
To prove her point, Henn used a genetic model trained to predict skin color from DNA and used it among southern African populations, and found that “it literally predicted that people with the darkest skins would have the lightest skin.”
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