A new research has indicated that human evolution is speeding up instead of slowing down or halting, indicating that humans on different continents are becoming increasingly different.
The research was conducted by a team led by John Hawks, an anthropologist from the University of Wisconsin-Madison.
"We used a new genomic technology to show that humans are evolving rapidly, and that the pace of change has accelerated a lot in the last 40,000 years, especially since the end of the Ice Age roughly 10,000 years ago," says research team leader Henry Harpending, professor of anthropology at the University of Utah.
The researchers built a case that human evolution has accelerated by comparing genetic data with what the data should look like if human evolution had been constant:
If evolution had been fast and constant for a long time, there should be many recently evolved genes that have spread to everyone. Yet, the study revealed many genes still becoming more frequent in the population, indicating a recent evolutionary speedup.
Next, the researchers examined the history of human population size on each continent. They found that mutation patterns seen in the genome data were consistent with the hypothesis that evolution is faster in larger populations.
"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," it adds.
The research estimates that positive selection just in the past 5,000 years alone - around the period of the Stone Age - has occurred at a rate roughly 100 times higher than any other period of human evolution. Many of the new genetic adjustments are occurring around changes in the human diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilizations.
"In evolutionary terms, cultures that grow slowly are at a disadvantage, but the massive growth of human populations has led to far more genetic mutations," said Hawks. "And every mutation that is advantageous to people has a chance of being selected and driven toward fixation. What we are catching is an exceptional time," he added.
The research team analyzed data from the International HapMap Project, short for haplotype mapping. This project is working to catalog genetic similarities and differences in human beings by studying genes from distinct sample populations around the globe.
"Because human population grew from several million at the end of the Ice Age to 6 billion now, more favored new genes have emerged and evolution has speeded up, both globally and among continental groups of people," said Harpending. "We have to understand genetic change in order to understand history," he added.
But according to Harpending, the speedup in human evolution is more or less a temporary state of affairs.
"That's because of our new environments since the dispersal of modern humans 40,000 years ago and especially since the invention of agriculture 12,000 years ago. That changed our diet and changed our social systems," said Harpending. "If you suddenly take hunter-gatherers and give them a diet of corn, they frequently get diabetes. We're still adapting to that. Several new genes we see spreading through the population are involved with helping us prosper with high-carbohydrate diet," he added.