Our Stone Age ancestors were more genetically similar to Neanderthals than they are to us, as our species has evolved 100 times faster in the past 5,000 years than at any other time in human evolution, a new study indicates.
Conventional wisdom has held that human evolution slowed as modern humans emerged and even stopped with us, but genetic data is now showing that the opposite is true, with aspects of our cultures, such as diet and medicine, and the ballooning human population pushing the gas pedal on the evolution of our species.
Anthropologist John Hawks of the University of Wisconsin-Madison and his colleagues analyzed data from the International HapMap Project, which works to catalog the genetic similarities and differences among humans from cultures around the globe—this map of genetic variation can give insight into changes in human genes over time.
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DNA is constantly being reshuffled via recombination, so researchers examine genetic changes over evolutionary time by locating long sequences of DNA variations—because they are uninterrupted, they seem to have been positively selected for over time.
Hawks and his team found evidence of recent selection on approximately 1,800 genes, or 7 percent of all human genes.
One example of such a gene is lactase, which helps people digest milk. The gene normally declines and stops all activity in the teen years, said Hawks. But northern Europeans developed a variation that allowed them to drink milk their whole lives—a relatively new adaptation that resulted from domestic farming.
The biggest new pathway for selection relates to disease resistance, Hawks said. As people started living in large communities about 10,000 years ago, epidemic diseases such as malaria, smallpox and cholera, swept through and changed patterns of human mortality. As a result, humans with genetic adaptations for resistance to these diseases were selected for.
Another recently discovered gene, CCR5, which makes people resistant to HIV/AIDS, originated about 4,000 years ago and now exists in about 10 percent of the European population.
"There are many things under selection that are making it harder for pathogens to kills us," Hawks said.
Population explosion
The huge growth of the human population is making all these changes occur faster because large populations have more genetic variation, Hawks said. Only a few million humans lived on the planet 10,000 years ago. This number hit 200 million people at 0 A.D., 600 million people in 1700 and today it has risen to more than 6.5 billion people.
"What's really amazing about humans, that is not true with most other species, is that for a long time we were just a little ape species in one corner of Africa and weren't genetically sampling anything like the potential we have now," Hawks said.
The most recent changes in the past 5,000 years are the most striking, according to Hawks.
"Five thousand years is such a small sliver of time—it's 100 to 200 generations ago," he said. "That's how long it's been since some of these genes originated, and today they are in 30 to 40 percent of people because they've had such an advantage. It's like 'Invasion of the Body Snatchers.'"
The findings were published online today by the Proceedings of the National Academy of Sciences.
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