CHICAGO (AFP) — The world may feel more and more like a global village, but its residents are increasingly genetically diverse thanks to the rapidly accelerating pace of human evolution, a study said Monday.
Geneticists say the huge explosion in our numbers in the past 40,000 years, since Homo sapiens migrated out of Africa to other continents, has resulted in a much faster pace of evolution compared to the previous six million years.
The pace of change has increased 100-fold in modern times compared to our distant past, and most notably since the Ice Age, 10,000 years ago, and has led to increasing diversification between the races.
"We are more different genetically from people living 5,000 years ago than they were different from Neanderthals," said John Hawks, an anthropologist at the University of Wisconsin-Madison who collaborated on the study.
The findings are based on analysis of data from an international genomics project. A team of scientists examined DNA from 270 individuals in four ethnically different populations to see how genetic variations or SNPs (single nucleotide polymorphisms) evolved over time.
Contrary to conventional wisdom, which holds that human evolution has slowed to a crawl or even stopped in modern humans, the researchers' analysis suggested that the process of natural selection has sped up.
"Rapid population growth has been coupled with vast changes in cultures and ecology, creating new opportunities for adaptation," the authors wrote in the paper in the Proceedings of the National Academy of Sciences.
"The past 10,000 years have seen rapid skeletal and dental evolution in human populations, as well as the appearance of many new genetic responses to diet and disease."
Human migrations into new European and Asian environments created selective pressures favoring less skin pigmentation (so more sunlight could be absorbed through the skin to make Vitamin D), adaptation to cold weather and dietary changes.
One example of a genetic adaptation to human culture involves the gene that makes the milk-digesting enzyme lactase.
The gene normally stops activity about the time a person becomes a teenager, but northern Europeans developed a variation of the gene that allowed them to drink milk their whole lives -- a relatively new adaptation that is directly tied to the introduction of domestic farming and use of milk as an agricultural product.
"Human races are evolving away from each other," said Henry Harpending, an anthropology professor at the University of Utah in Salt Lake City.
"Genes are evolving fast in Europe, Asia and Africa, but almost all of these are unique to their continent of origin. We are getting less alike, not merging into a single, mixed humanity."
He said that is happening because humans dispersed from Africa to other regions 40,000 years ago and "there has not been much flow of genes between the regions since then."
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