European humans have become "whiter" in the past 5,000 years, undergoing a distinct change in their DNA due to natural selection, according to scientists.
In research published this week in the journal Proceedings of the National Academy of Sciences, experts analysed DNA taken from ancient skeletons and compared it with the current European human genome.
Teams from University College London and Mainz found that there were striking differences over time in the genes which are associated with hair, skin and eye pigmentation.
Sandra Wilde, the lead report author from Mainz's Johannes Gutenberg University, told Science Daily: "Prehistoric Europeans in the region we studied would have been consistently darker than their descendants today.
"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."
The team said that while geneticists have been tracking the "echoes" of natural selection in humans for a number of years, this was the first time results could be pinned accurately to a specific timeframe.
Working with archaeologists from Berlin and Kiev, they used computer simulations to join the dots between data. Where the genetic changes could not be explained by the randomness of inheritance, the researchers were able to infer that positive selection played a role.
The report authors said there were a number of possible explanations for why this change came about. UCL's Professor Mark Thomas said: "Perhaps the most obvious is that this is the result of adaptation to the reduced level of sunlight in northern latitudes."
Professor Thomas explained that the amount of vitamin D taken in through UV exposure by lighter skin compared to darker skin might have made the former "the best option".
But Wilde added: "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."
The team said their findings backed the theory that the quirks of a group's preferences often have a greater impact on sexual selection than the natural environment.