You're All Mutants Out There - And That's A Good Thing

The fantastically swift and widespread mutation that gave 30% of the world's humans tolerance to lactose as adults is one indicator that human evolution has speeded up in recent years.

That's the conclusion that anthropologist Gregory Cochran and his team from the University of Utah has drawn in a highly controversial new study that just appeared in the online version of the journal Proceedings of the National Academy of Sciences. Here he is quoted by David Biello of Scientific American:

"We found very many human genes undergoing selection. Most are very recent, so much so that the rate of human evolution over the past few thousand years is far greater than it has been over the past few million years."

Ann Gibbons at ScienceNow summarized some of the conclusions.

Evolution has accelerated in 1800 human genes, which encompass about 7% of the human genome, [paleontologist Harry] Harpending's team reports online this week in the Proceedings of the National Academy of Sciences. Most of the mutations resulted from dramatic population booms, they suggest. As populations expand, the number of mutations increases, boosting the chances for a beneficial genetic variant that can improve survival and sweep through a population (in the same way that a large population of insects develops a gene for resistance to a pesticide faster than a small population).

Although the researchers don't know the identity of most of the genes, they say quite a few appear to be responses to changes in diet and a new wave of virulent diseases that swept through human populations as they began farming. Some examples include mutations that allow adults to digest starch, fatty acids, and lactose in milk, including mutations that arose in Europeans. Others improve the resistance to diseases, such as malaria, AIDS, and yellow fever in Africans. Several genes related to the production of human sperm also have been under selection in the past 10,000 years. Overall, "the pace of change has accelerated a lot in the last 40,000 years, especially since the end of the Ice Age," says Harpending.

The ability to drink milk as an adult has obvious survival advantages, especially in locations with otherwise poor resources and access to important nutrients, such as calcium. Far from milk being a poison, it helped spread humanity across the globe.

Cochran also said:

"We believe that this can be explained by an increase in the strength of selection as people became agriculturalists—a major ecological change—and a vast increase in the number of favorable mutations as agriculture led to increased population size.

Biello reports that:

Roughly 10,000 years ago, humanity made the transition from living off the land to actively raising crops and domesticated animals. Because this concentrated populations, diseases such as malaria, smallpox and tuberculosis, among others, became more virulent. At the same time, the new agriculturally based diet offered its own challenges—including iron deficiency from lack of meat, cavities and, ultimately, shorter stature due to poor nutrition, says anthropologist John Hawks of the University of Wisconsin–Madison, another team member.

"Their bodies and teeth shrank. Their brains shrank, too," he adds. "But they started to get new alleles [alternative gene forms] that helped them digest the food more efficiently. New protective alleles allowed a fraction of people to survive the dread illnesses better."

Milk drinking equaled survival. It's still not a bad way to get your nutrients. It's not essential, and no one is claiming that it is today. But it's certainly not poison. Or something that is only for baby cows. Science indicates otherwise.

Note: the controversial part of the study is only whether the speeded up evolution is to be found in so many many parts of the genome.

"I don't deny recent rapid selection," says geneticist Kenneth Kidd of Yale University. "But I am not yet convinced that so much rapid selection at so many places in the genome has occurred. ... I think we need much more data."

The conclusions about milk are all my own. They may be controversial to some, I suppose, but seem obvious and solid to me.