A Briton who lived 10,000 years ago had dark brown skin and blue eyes. At least, that鈥檚 what dozens of news stories published this month 鈥� including our own 鈥� stated as fact. But one of the geneticists who performed the research says the conclusion is less certain, and according to others we are not even close to knowing the skin colour of any ancient human.
The skeleton of Cheddar Man was discovered in 1903 in a cave in south-west England where it had lain for 10,000 years.
Until a few weeks ago, he had always been . This makes some sense, given that people living at northern latitudes often have paler skins. The explanation may be that it allows more of the weak northerly sunlight into their skin, so they can make enough vitamin D. And it seems our species reached Europe 30,000 years before Cheddar Man lived, so his ancestors would have had plenty of time to evolve paler skins.
Advertisement
But the new DNA analysis suggests that Cheddar Man may have had dark skin. Most news stories said his skin was 鈥渄ark to black鈥�.
Giveaway genes
To show this, researchers including at Indiana University鈥揚urdue University Indianapolis read Cheddar Man鈥檚 DNA. Walsh had helped develop a model that attempts to predict someone鈥檚 eye, hair and skin pigmentation solely from their DNA, and the team applied this model to Cheddar Man.
The most recent version of the model was . It focuses on 36 spots in 16 genes, all linked to skin colour.
To test it, Walsh and her colleagues took genetic data from over 1400 people, mainly from Europe and the US but also some from Africa and Papua New Guinea. The team used part of the data to 鈥渢rain鈥� their model on how skin colour and the 36 DNA markers are linked. They then used the rest of the data to test how well the model could predict skin colour from DNA alone. The model correctly identified who had 鈥渓ight鈥� skin or 鈥渄ark-black鈥� skin, with a small margin of error.
When Walsh and her colleagues applied the model to Cheddar Man, they concluded his skin colour fell between 鈥渄ark鈥� and 鈥渄ark to black鈥�.
Not so sure
The research was first announced by press release, to coincide with the release of a TV documentary. It has now been posted to a preprint server ().
Walsh stresses that the study doesn鈥檛 conclusively demonstrate Cheddar Man had dark to black skin. We cannot place such confidence in the DNA analysis, she says. For one thing, Cheddar Man鈥檚 DNA has degraded over the last 10,000 years.
鈥淚t鈥檚 not a simple statement of 鈥榯his person was dark-skinned鈥�,鈥� says Walsh. 鈥淚t is his most probable profile, based on current research.鈥�
In fact, we are not ready to predict the skin colour of prehistoric people just from their genes, says at Stony Brook University, New York. That鈥檚 because the genetics of skin pigmentation turn out to be more complex than thought.
Too many genes
In November 2017, Henn and her colleagues exploring the genetics of skin pigmentation in populations indigenous to southern Africa 鈥� where skin colour varies more than many people appreciate. Just weeks before, a group led by at the University of Pennsylvania in Philadelphia had published a paper on the genetics of skin pigmentation in people from eastern and southern Africa.
鈥淭he conclusions were really the same,鈥� says Henn. 鈥淜nown skin pigmentation genes, discovered primarily in East Asian and European populations, don鈥檛 explain the variation in skin pigmentation in African populations. The idea that there are really only about 15 genes underlying skin pigmentation isn鈥檛 correct.鈥�
It now seems likely that many other genes affect skin colour. We don鈥檛 know how.
[video_player id=鈥漮Ptt13Tq鈥� access_level=鈥漵ubscriber鈥漖
If we are still learning about the link between genes and skin pigmentation in living populations, we can鈥檛 yet predict the skin colour of prehistoric people, says Henn.
This debate may seem of little practical importance 鈥� although the idea that Cheddar Man was dark-skinned generated . However, we need to know the limitations of this sort of genetic technology.
Police could one day plug DNA from a crime scene into one of these models to determine what a suspect looks like. Walsh鈥檚 model might succeed at this in the US, says Henn, because it was trained on DNA from people with similar ancestry to North Americans. But it may well fail elsewhere.
Henn鈥檚 team has tested an older model that aimed to predict skin colour from DNA. When they put it to work among southern African populations, 鈥渋t literally predicted that people with the darkest skins would have the lightest skin.鈥�
