ARE humans still evolving? Because evolution usually takes many generations, it is hard to tell. But two new genetic studies reveal DNA changes that took hold within the last few thousand years, suggesting that modern lifestyles have recently shaped our evolution 鈥� and are probably still doing so.
鈥淒uring a short time, human genomes have changed a lot,鈥� says Irina Morozova of the University of Zurich in Switzerland. 鈥淲e think these changes are driven by human civilisation.鈥�
Both studies looked for evidence of evolution favouring some DNA sequences over others, a process called selection.
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Morozova and her colleagues compared the genomes of 150 Europeans from between 5500 and 3000 years ago with those of 305 modern Europeans descended from them. This allowed the team to identify various processes that evolution has acted on in Europeans within the past 6000 years (Molecular Biology and Evolution, ).
The team found changes over time in the way that the body metabolises carbohydrates. Morozova suggests these happened when societies began farming, prompting a switch from a meat-heavy, hunter-gatherer diet to a starchier, more sugary one. She thinks human metabolism is still evolving, and may keep doing so for millennia. 鈥淚t鈥檚 not like we鈥檙e completely adapted to this.鈥�
There was evidence of evolutionary changes in several aspects of the immune system, too. It鈥檚 not clear what these changes do, but they could have been a response to exposure to new diseases some 6000 years ago, when people began living in more crowded conditions and spending more time with livestock.
But two processes stood out as showing very few evolutionary changes over the same period of time. These are how egg cells form, and long-term potentiation, a process in the brain that aids learning by strengthening the connections of commonly used neural pathways. It looks as if both have been protected from changing, says Morozova.
In the second study, Fernando Racimo at the University of Copenhagen in Denmark and his colleagues developed a new way to detect selection in modern human genomes, even when their ancestral populations have split and merged throughout history (bioRxiv, ).
They discovered that SLC45A2, a gene variant involved in skin and eye colour, became more common in early Europeans. This suggests it played a role in the evolution of paler skin, which is thought to have arisen within the past 10,000 years.
They also identified many genes that seem to have been evolving relatively recently in East Asian groups, whose genetic history has not been as well studied as that of ancestral Europeans. Several are involved in the immune system. 鈥淭hey have to do with how the body learns to respond to new threats,鈥� says Racimo.
Evolution during the last few hundred years is harder to spot because the signals are weaker, but Racimo says humans are definitely still evolving. 鈥淭he question is, what are the selective pressures that are driving the evolution? They鈥檙e probably very different from the selective pressures we were experiencing 5000 to 10,000 years ago.鈥�
This article appeared in print under the headline 鈥淐ivilisation shaped human evolution鈥�
