Almost three quarters of gene mutations occurred within the last 5 to 10 millennia of humans’ 200,000 years existence, and those of European descent have most of the harmful ones, an analysis of people in the U.S. showed.
About 14 percent of mutations scientists identified were found to be harmful, according to a gene study of 6,500 Americans published today in the journal Nature. About 86 percent of those variants arose in people with European heritage in the last 5,000 years, the research found.
The exploding population growth of humans enabled DNA errors to occur more rapidly, said study author Joshua Akey, an associate professor of genome sciences at the University of Washington in Seattle. People with European ancestry have most of the new deleterious mutations because the population boom among Europeans was more recent and natural selection hasn’t yet removed them, he said.
“There’s an enormous amount of recently arisen, rare mutations that’s directly attributable to the explosive population growth over the last two to four generations,” said Akey in a telephone interview.
The world’s population was 6.9 billion in 2010, more than doubling from 2.5 billion in 1950, according to United Nations data. The population boom may mean that unusual combinations may affect more people, numerically, while remaining rare relative to the world population, Akey said.
More people allow for rare variations to come up more often and for new mutations to appear, Akey said. The growing population also makes it more likely that new mutations will be introduced, such as those linked to autism, leading to an increase in certain diseases.
The findings are also consistent with the “out of Africa” hypothesis of human evolution, which holds that modern humans emerged in Africa before spreading across the rest of the world, according to the researchers. Events such as the Black Death, a plague which killed about a third of the people in Europe, could be seen through their effects on the genome, said Eric Topol, a professor of translational genomics at the Scripps Research Institute in La Jolla, California.
Today’s data may provide other hints of how the human population expanded, much like tree rings can provide records of the past weather, Topol said.
“This helps us understand bottlenecks and how humans evolved,” Topol said. He wasn’t involved in the study. Now when scientists see new genes or mutations, they “can also begin to ask when did they crop up,” he said.
What’s more, the data may help doctors identify the genetic basis of disease, he said. Researchers typically look for frequent variants in common ailments, such as diabetes and heart disease. Today’s results suggest that rare variations occur so often that they contribute more than once thought to common illnesses.
Because changes in the population have been so rapid and studies until this point relied on much smaller samples, scientists haven’t been able to detect increasing mutations.
For instance, scientists know from skeletons that humans have gotten larger over the last 1,000 years, though smaller analyses of the exome, the part of the genome that codes proteins, didn’t find any signs of that growth in their data.
“It turns out the reason we couldn’t see it before is because the growth happened so recently that you need thousands to see it,” Akey said. “There’s a massive signature of growth.”
The project, funded by the National Heart, Lung, and Institute Blood, was begun in September 2008. Further research may include sequencing parts of the genome that don’t code for proteins, Akey said. Some of these non-coding regions regulate the genes that code proteins, and may also be important.