If you judge the progress of humanity by Homer Simpson, Paris Hilton, and Girls Gone Wild videos, you might conclude that our evolution has stalled—or even shifted into reverse. Not so, scientists say. Humans are evolving faster than ever before, picking up new genetic traits and talents that may help us survive a turbulent future.
Much remodeling has gone on since the dawn of agriculture about 10 millenniums ago. "People who lived 10,000 years ago were much more like Neanderthals than we are like those people," says John Hawks, a professor of anthropology at the University of Wisconsin. "We've changed."
Hawks is among a growing number of scientists who are using whole-genome sequencing and other modern technologies to zero in on just how we've changed. Their research is helping illuminate not only how humans became what we are but also where we might be headed. For instance, some scientists speculate that changes in human mating patterns may be contributing to the increase in autism. Others track how humans have morphed in response to changing circumstances, including enhanced abilities to metabolize sugar and fight disease. Some people are genetically more resistant to the HIV virus, for instance, and that trait should become more common in the future, as those people are more likely to survive and have children who are resistant. Yet for some people, the makeover isn't big enough or fast enough. Some parents have started using DNA testing to choose the genetic makeup of their children, rejecting embryos with inherited flaws or embracing those with desired traits—such as being the right sex.
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.
It's even possible that very recent changes in society and the workplace could underpin the recent rise in cases of autism. Simon Baron-Cohen, director of the Autism Research Centre at the University of Cambridge, was struck by how many of the parents of children with autism who he tested were really good "systematizers"—people who understand the world according to rules or laws. They also were more likely to have a father who worked in engineering. He wonders if the increase in autism diagnoses could be partly due to "assortative mating"—that is, people picking mates like themselves. People with autism spectrum disorder are often detail oriented and analytical, and today they might have an easier time finding a spouse with similar abilities than they would have in past eras. Baron-Cohen notes that in the late 1950s, only 2 percent of the undergraduates at Massachusetts Institute of Technology were women; now, 50 percent are. So, he's setting up a study to test whether assortative mating among people with a genetic predisposition for autism could be fueling the birth of more children with autism.