Scientists have traditionally thought that the speed of human evolution has been relatively unchanged over the millions of years that humanoid species have been on Earth. New research, however, indicates that this isn’t the case and that human beings have evolved more rapidly in the past 10,000 years than it had in the past:
If evolution had been proceeding steadily at the current rate since humans and chimps separated 6 million years ago there should be 160 times more differences than the researchers found.
That indicates that human evolution had been slower in the distant past, Harpending explained.
“Rapid population growth has been coupled with vast changes in cultures and ecology, creating new opportunities for adaptation,” the study says. “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.”
And they found that different changes are occurring in Africans, Asians and Europeans.
The most obvious adaptation, of course, is skin color, which can be traced to the fact that humanity evolved in Europe and Asia to allow for greater absorption of Vitamin D in climates where the sun was not as warm, but the research also indicates other adaptations that helped humans survive in new environments:
In another example, the researchers noted that in China and most of Africa, few people can digest fresh milk into adulthood. Yet in Sweden and Denmark, the gene that makes the milk-digesting enzyme lactase remains active, so almost everyone can drink fresh milk, explaining why dairy farming is more common in Europe than in the Mediterranean and Africa, Harpending says.
And, as humans expanded into other environments, they developed other traits favorable to surviving there.
Far from being a static force that moves at a glacial pace, it’s clear from reports like this that evolution and natural selection are active forces that continue to shape who we are.
Update: Further details from Scientific American:
Roughly 10,000 years ago, humanity made the transition from living off the land to actively raising crops and domesticated animals. Because this concentrated populations, diseases such as malaria, smallpox and tuberculosis, among others, became more virulent. At the same time, the new agriculturally based diet offered its own challenges—including iron deficiency from lack of meat, cavities and, ultimately, shorter stature due to poor nutrition, says anthropologist John Hawks of the University of Wisconsin–Madison, another team member.
“Their bodies and teeth shrank. Their brains shrank, too,” he adds. “But they started to get new alleles [alternative gene forms] that helped them digest the food more efficiently. New protective alleles allowed a fraction of people to survive the dread illnesses better.”
By looking for wide swaths of genetic material that vary little from individual to individual within these sections of great variation, the researchers identified regions that both originated recently and conferred some kind of advantage (because they became common rapidly). For example, the gene known as LCT gave adults the ability to digest milk and G6PD offered some protection against the malaria caused by Plasmodium falciparum parasite.
“Ten thousand years ago, no one on planet Earth had blue eyes,” Hawks notes, because that gene—OCA2—had not yet developed. “We are different from people who lived only 400 generations ago in ways that are very obvious; that you can see with your eyes.”
Unless your name is Mike Huckabee
