Study in Public Library of Science Genetics suggests that humans have undergone a lot of adaptation in the last 200,000 years.
Adaptation and not neutral, random selection of genes is a critical part of human genomic evolution, according to geneticists at Stanford.
In the past, researchers would find changes in specific genes suggesting that recent adaptations in humans might be common but could not find genome-wide signatures of pervasive adaptation. Estimates of the degree of adaptation in humans ranged from as high as 30% and all the way down to zero. Signatures were impossible to interpret with confidence.
In this study, scientists found the adaptation signal by locating regions of the genome that hitchhiked along with an adaptation. The team detected a number of signatures that suggest adaptation is quite pervasive and common.
“Others have looked for the signal of widespread adaptation and couldn’t find it,” points out Dmitri Petrov, Ph.D., associate professor of biology at Stanford University and one of two senior authors of the paper. “Now we’ve used a lot more data and did a lot of work cleaning it up. We were able to detect the adaptation signatures quite clearly, and they have the characteristic shape we anticipated.”
When a genetic adaptation occurs and is passed on to offspring, other genes on both sides of the adaptation typically accompany it. The result is a whole region of the genome unusually similar in all humans. This scenario is referred to as a selective sweep, and researchers can identify and trace it through human genetic history.
“Adaptation becomes widespread in the population very quickly,” Dr. Petrov notes. “Whereas neutral random mutation doesn’t and would not have the selective sweep signature.”
The team found these regions of unusual similarity among all humans in particular places in the genome as theory has predicted. “The work suggests human beings have undergone rampant adaptation to their environment in the last 200,000 years of history,” according to Dr. Petrov.
Researchers should now be able to do a better job of finding the regions within the genome responsible for specific human adaptations such as lactose tolerance or skin pigmentation, which are related to changes in human history or past environments.
“As the data are going to grow, we should be able to locate specific adaptive events quite well,” says Dr. Petrov “By identifying specific genes, we can unravel this evolutionary history of adaptive change.”
This paper is published January 16 online in Public Library of Science Genetics.