Animal Provides Genetic Clue to Recent Human Evolution
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Scientists may have found a clue for discovering the incidence of recent human evolution. Researchers were able to find a single mutation that produces several traits common in East Asian peoples, from thicker hair to denser sweat glands.
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The findings, published in the journal Cell, examined a mutation that had previously been identified as a strong candidate for positive selection. That is, the mutation would have given an evolutionary advantage to individuals. The mutation itself was for an ectodysplasin receptor, or EDAR, which was part of a signaling pathway known to play a role in the development of hair, sweat glands and other skin features. Although human populations in Africa and Europe had one, most East Asian populations had a variant of it called EDAR370A, which studies linked to thicker scalp hair and altered tooth shape in humans.
In order to more fully examine this mutation, Yana Kamberov, one of the researchers, developed a mouse model with the exact mutation of EDAR370A. The researchers found that the mouse exhibited thicker hair, more densely branched mammary glands and an increased number of sweat glands. This prompted the scientists to examine similar traits in human populations. After examining the fingertips of Chinese volunteers who carried the gene, they found that their sweat glands were packed about 15 percent more densely than those of the control population.
It wasn't enough to find evidence of this trait, though. The team, which included collaborators at the University of College London, then used a computer model to predict when exactly this mutation arose. The models suggested that the variant emerged in central China between 13,175 and 39,575 years ago; the median estimate was 30,925 years ago. While the exact date is up for debate, researchers estimated it at least occurred 15,000 years ago, which predates the migration from Asia by Native Americans, who also carry the mutation.
So what does this mean exactly? It shows that it's possible that human evolution has occurred to some degree. The time span itself suggests that different traits could have been under selection at different times. Sweat glands may have conferred an advantage in new climates and a cultural preference for good hair may have occurred due to its link to other traits which made an individual more successful.
Moving forward, researchers hope to piece together how different selected mutations have impacted human diversity and why they occurred in the first place.