Not what they were

STUDYING recent human evolution can be frustrating. Take lactose tolerance—the ability of some people, particularly of European descent, to digest this sugar, found in milk, even into adulthood. In the evolutionary past the gene for lactase, the enzyme that does the digesting, normally got switched off in adults. But one variant (known as an allele) of the gene that does the switching off instead leaves the system running, conferring adult lactose tolerance. That lets this allele’s bearers consume a diet rich in dairy products, a useful trick for a species beginning to domesticate milk-producing animals. Genetic analysis shows that lactose tolerance emerged between 5,000 and 10,000 years ago. In evolutionary terms, it is thus extremely recent. In human terms, though, that timescale means how it spread and how this process intertwined with the rise of dairy farming are lost in the mists of prehistory.

It would be nice, therefore, to have a technique that could look at human evolution on a scale of centuries, rather than millennia. And on May 7th a team led by Jonathan Pritchard, a biologist at Stanford University, announced they had come up with one. In a paper posted to bioRxiv, they describe it, and also how they have used it to track ways the inhabitants of Britain have altered over the past 2,000 years.