Europeans had darker skin, hair, and eye pigmentation some 5,000 years ago, research shows.
Researchers analysing ancient DNA from skeletons found that selection had a significant effect on the human genome even during the past 5,000 years - resulting in sustained changes to the appearance of people.
For several years, population geneticists have been able to detect echoes of natural selection in the genomes of living humans, but those techniques are typically not very accurate about when that natural selection took place.
Anthropologists at Johannes Gutenberg University Mainz (JGU) in Germany and geneticists at University College London (UCL) decided to take a new approach.
This involved analysing DNA from archaeological skeletons and then comparing the pre-historic data with that of contemporary Europeans using computer simulations.
While investigating numerous genetic markers in archaeological and living individuals, Sandra Wilde from the JGU Institute of Anthropology noticed striking differences in genes associated with hair, skin and eye pigmentation.
“Pre-historic Europeans in the region we studied would have been consistently darker than their descendants today,” Wilde noted.
This is particularly interesting as the darker phenotype seems to have been preferred by evolution over hundreds of thousands of years. All our early ancestors were more darkly pigmented, she explained.
However, things must have changed in the last 50,000 years as humans began to migrate to northern latitudes.
"In Europe, we find a particularly wide range of genetic variation in terms of pigmentation," added Karola Kirsanow.
“Perhaps the most obvious is that this is the result of adaptation to the reduced level of sunlight in northern latitudes," added professor Mark Thomas of University College London.
Most people of the world make most of their vitamin D in their skin as a result of UV exposure.
But at northern latitudes and with dark skin, this would have been less efficient.
If people were not getting much vitamin D in their diet, then having lighter skin may have been the best option, Thomas noted.
But this vitamin D explanation seems less convincing when it comes to hair and eye colour.
Instead, it may be that lighter hair and eye colour functioned as a signal indicating group affiliation, which, in turn, played a role in the selection of a partner, said the study published in the journal Proceedings of the National Academy of Sciences (PNAS).