Several distinctive East Asian traits — thicker hair shafts, more sweat glands, characteristically identified teeth and smaller breasts — can be traced back to a mutation in the EDAR gene that occurred about 35,000 years ago:
The Broad team engineered a strain of mice whose EDAR gene had the same DNA change as the East Asian version of EDAR.
When the mice grew up, the researchers found they did indeed have thicker hair shafts, confirming that the changed gene was the cause of East Asians’ thicker hair. But the gene had several other effects, they report in Thursday’s issue of the journal Cell.
One was that the mice, to the researchers’ surprise, had extra sweat glands. A Chinese member of the team, Sijia Wang, then tested people in China and discovered that they, too, had more numerous sweat glands, evidently another effect of the gene.
Another surprise was that the engineered mice had less breast tissue, meaning that EDAR could be the reason that East Asian women have generally smaller breasts.
East Asians have distinctively shaped teeth for which their version of EDAR is probably responsible. But the mice were less helpful on this point; their teeth are so different from humans’ that the researchers could not see any specific change.
The finding that the gene has so many effects raises the question of which one was the dominant trigger for natural selection.
Dr. Sabeti said the extra sweat glands could have been the feature favored by natural selection, with all the other effects being dragged along in its train.