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Genetic evidence shows that human evolution has been speeding up during the past 10,000 years, indicating that humans on different continents are becoming less alike, according to a report by two U professors that was published last month.
The rapid increase in human population from about five to 10 million 10,000 years ago to billions of people today is the result of several different factors, said Gregory Cochran, a biologist and professor of anthropology at the U, in the Dec. 10 issue of Proceedings of the National Academy of Sciences.
First, groups that went from hunters to farmers had more access to food and a diverse diet. A greater food supply led to more rapid population growth among certain groups, putting them at an advantage in comparison to groups that solely relied on hunting.
Other groups were able to develop a gene that allowed them to digest milk, causing them to evolve faster. Most humans were not able to digest milk after about age 5, but, between 5,000 and8,000 years ago, in an area close to southern Russia, some cattle herders developed the ability to digest milk, Cochran said.
As centuries passed, the descendants of this group of farmers and milk drinkers had developed a genetic advantage that allowed them to better digest a number of carbohydrates, including dairy.
"Those that switched to dairy had access to two-and-a-half times more food," Cochran said.
As a result, those groups were able to feed a population more than double the size of other groups, giving them a big advantage in taking control of their neighbors, Cochran said.
This group of people, the Indo-Europeans, was able to settle across Europe, Persia, central Asia and into northern India. Although a small number of African tribes around the area of present-day Sudan were able to develop the ability to digest milk, many people in Africa and China still have a problem digesting milk into adulthood, the study said.
"(The findings) can lead to a profound change in our outlooks on history," said Henry Harpending, a professor of anthropology at the U. "In another few decades, historians will have to understand genetics."
Cochran said that people are now evolving 100 times faster than in the past, and differences in how certain groups metabolize foods like carbohydrates, alcohol and milk are clear.
Harpending and Cochran conducted the study with anthropologist John Hawks, a former U postdoctoral researcher now at the University of Wisconsin, Madison, geneticist Eric Wang of Affymetrix Inc. in California and biochemist Robert Moyzis from the University of California, Irvine.
The researchers collected data from 3.9 million chromosome mutations from 270 people in four different populations, including Han Chinese, Japanese, the Yoruba tribe in Africa and northern Europeans.
After researching the history of human populations on every continent, they found that the data were consistent with their hypothesis that evolution is faster in certain larger populations.
Harpending and Cochran published a controversial study in 2005 that argued that northern European Jews developed above-average intelligence genetically. For 900 years, Jews from that area of the world were forced into jobs in finance, tax collection, trade and management, they argued.
An article in The New York Times about the study quoted one Harvard scholar who said the research is "politically incorrect" but shouldn't be dismissed.
Harpending didn't deny the controversial nature of the topic and said that more research of this nature from the scientific community will surface.
"New perspectives and understandings will come out of the woodwork in the next 10 years," Harpending said. "We violated a taboo by releasing that information. It's not good to have secret knowledge. You have to tell everyone the truth."
Harpending said that genetic differences among different human groups cannot be used to justify discrimination or inequality, but different ethnic groups generally don't perform the same in all areas.
"I think that human groups are different," Harpending said. "You can't predict a lot about individuals, but the idea that all groups are equal is a fantasy."
c.mayorga@chronicle.utah.edu
