Where Is Human Evolution Heading?

The race's DNA is changing faster than ever; what it means for our descendants.

Video Channel: Science




New mutations. Until recently, anthropologists thought that human evolution had slowed down. But last December, Hawks reported that it has actually accelerated 100-fold in the past 5,000 to 10,000 years. He figured that out by comparing chunks of DNA among 269 people from around the world. Over time, DNA accumulates random mutations, just as the front of a white T-shirt tends to accumulate spots. The bigger the chunks of DNA without random spots, the more recently it had been minted. Using this system, Hawks concluded that recent genetic changes account for about 7 percent of the human genome. Much of the increase, he says, has been fueled by the growth of the world's population, which has expanded by a factor of 1,000 over the past 10,000 years. Having more people increases the odds of mutations.

At the same time, the human genome has been scrambling to adapt to a rapidly changing world—11,000 years ago, nobody farmed, nobody milked domesticated animals, and nobody lived in a city. People with a mutation that aided survival were more likely to thrive, reproduce, and pass that mutation along to offspring. For example, the capacity to digest lactose, the sugar in milk, has become common only over the past 3,000 years. Now, about 95 percent of the people in northern Germany have the mutation, which also popped up independently among the Masai in Africa and the Lapps in Finland. Hawks says: "This is really rapid evolution."

Humans will continue to change to cope with new diseases, if history is any guide. Genes that defend against infectious disease have been among the most rapidly evolving parts of the human genome. People whose ancestors lived in European cities are more likely to have some resistance to smallpox, while people in sub-Saharan Africa are more likely to be genetically resistant to malaria. Just weeks ago, researchers reported that one genetic variant that protects against malaria also makes people more susceptible to AIDS, a discovery that could lead to tailored treatment for AIDS in Africa.

Right now, our genes are playing catch-up against modern scourges—like diabetes. Native Americans and Polynesians, whose cultures only recently adopted a European-style diet of refined grains, have the world's highest rates of diabetes. The theory is that the "thrifty genes" that helped those groups survive famines haven't had time to adapt to the glucose spikes caused by eating starchy food. "How we move sugars around and how we burn them has really changed a lot," says Gregory Wray, an evolutionary biologist at Duke University.