Articles in Reuters and the BBC, reporting on a paper published in the Proceedings of the National Academy of Sciences, describe how the pace of human evolution has increased in the last 5000 years. However, the changes discussed have taken the form of adaptations specific to certain regions, with the result that the human species is becoming less similar.
From the BBC:
In the past 5,000 years, genetic change has occurred at a rate roughly 100 times higher than any other period, say scientists in the US.
This is in contrast with the widely-held belief that recent human evolution has halted….
Professor Henry Harpending, an author of the study from the University of Utah, Salt Lake City, US, said: “The dogma has been these [differences] are cultural fluctuations, but almost any temperament trait you look at is under strong genetic influences.
“Genes are evolving fast in Europe, Asia and Africa, but almost all of these are unique to their continent of origin,” he added. “We are getting less alike, not merging into a single, mixed humanity.”
This is happening, he said, because “there has not been much flow” between different regions since modern humans left Africa to colonise the rest of the world. And there is no evidence that it is slowing down, he added.
“The technology can’t detect anything beyond about 2,000 years ago, but we see no sign of [human evolution] slowing down. So I would suspect it is continuing,” he told BBC News.
Researchers found evidence of recent selection in 7% of all human genes, including lighter skin and blue eyes in northern Europe and partial resistance to diseases, such as malaria, among some African populations.
“Five thousand years is such a small sliver of time,” said co-author Professor John Hawks of the University of Wisconsin, Madison. “It’s 100 or 200 generations ago. That’s how long since some of these genes originated, and today they are [in] 30% or 40% of people because they’ve had such an advantage.”
The researchers propose that there are two factors causing human evolution to speed up.
“One of them is there are a lot more people – the more people you have the more opportunities there are for an advantageous mutation to show up,” said Professor Harpending.
A large population has more genetic variation and allows for more positive selection than a small one.
“The second is environmental change – our diets have changed, we are in radically new environments,” he added. “With a large population size comes lots of new diseases.”
However, geneticist Professor Steve Jones of University College London said suggesting a large population size could increase the speed of evolution was “a contentious issue”.
“Once a population gets above a very small size it is not very clear if its ability to respond to natural selection depends on size,” he told BBC News….
“At the moment we are in an evolutionary interval. We are in between two storms. One storm has more or less blown itself out, the storm of farming.
“The question is whether we are going to stay in the calms or whether another great storm will start. And if there is one, I would say it is most certainly to do with epidemic disease.”