According to the New York Times, the journal Cell has recently published a study on the mutation of the EDAR gene. This mutation, known as EDARV370A, is responsible for part of the characteristic phenotypes of Eastern Asian and Native American humans. Mutation of the EDAR gene causes hair shafts to be thicker, teeth to be shaped differently, and more sweat glands to develop. It is likely that the EDAR mutation allowed these populations to diverge from Europeans and Africans approximately 35,000 years ago.
In the Cell article, the EDAR370A mutation was tested in mice. When the gene was altered to completely remove function in vivo, the result was improper hair development, and absence of sweat glands and teeth. In contrast, mice with a mutant copy of EDAR370A had thicker hair roots and an increased number of eccrine glands. Interestingly, homozygotes for 370A showed increased branching of mammary tissue coupled with smaller mammary fat pads. Further testing showed this EDAR mutation is a "gain of function" model, and that specimens with a single copy of the mutation showed a lessened but significant level of the traits. The authors of the study in Cell tested the genotype of several Han Chinese individuals, and found that the physical characteristics present in mice with an EDAR mutation were also carried over to humans.(Kamberav, et al.)
There are several theories for why this mutation may have been selected. Some scientists believe that thicker hair may have been beneficial in cold areas, although the dating of the mutation makes this theory unlikely. Another belief is that thicker hair and smaller breast size are sexually selected characteristics, similar to blond hair in Europeans. A third scientist believes that each of the mutations on the EDAR gene may have occurred at a different time, and over many generations the entire genotype became common. As researchers move forward, they will continue to try to understand why this gene was selected for.
Chart A from the article in Cell shows the distribution of the EDAR370A mutation. Blue marks indicate the standard allele, while red is the 370A form. Chart B is a heat map showing the density of the trait on the Asian continent. (Kamberav, et al.)
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Sources:
Kamberav, Yana G., Sijia Wang, Jingze Tan, et al. "Modeling Recent Human Evolution in Mice by Expression of a Selected EDAR Variant". Cell. Volume 152, Issue 4: 691-702.
Wade, Nicholas. "NY Times - East Asian Physical Traits Linked to 35,000-Year-Old Mutation"
New York Times. Feb. 14, 2013.
So does this study imply that Native Americans came to the American continent from East Asia? From what I've read previously, the ancestors of Native Americans were thought to have crossed the Bering Strait, which is much farther north from the traditional Han Chinese borders.
ReplyDeleteThis is fascinating! Did you happen to come about other studies that discuss the genetic mutations that led to the phenotype characteristics seen in other races and ethnic groups? Studying such mutations could tell us a lot about the history of different groups.
ReplyDelete-Mary Morales
Aydan:
ReplyDeleteThat's an interesting observation. I did a little bit of research on the timing of human migration. Most sources seem to claim that humans crossed the Bering land bridge around 15,000-17,000 years ago. The article states that the EDAR mutation emerged roughly 35,000 years ago. Although I do not want to draw any inappropriate conclusions, it may be safe to assume that the EDAR genotype was around well before any humans migrated to North America.
Mary:
This journal article is supposedly part of a coming series that looks at the mutations that led to characteristic phenotypes of different ethnic groups. I believe that this is the first such article published in the series, but it more may be coming in the next few months.
What is confusing to me is that the development of thicker hair could be in response to the colder weather, but isn't the development of more sweat glands a response to a warmer weather? The density of this mutation seems to be concentrated in the temperate region, where it is not extremely cold or hot (with all 4 seasons).
ReplyDeleteGood point! This was brought up in the NYT article. The authors of the study believe that while the evolution of sweat glands was likely a response to frequently humid temperatures in China 35,000 years ago. Thicker hair could be a byproduct of sexual selection.
DeleteI am curious as to how it evolved as well. Maybe an instance of genetic drift? It would be cool to see how all different "races" separated over human history. Humans have very diverse physical appearances. It is interesting to see how something as simple as skin color that has caused so many social battles has evolutionary roots from the past.
ReplyDeleteAre these characteristics still prominent in populations of humans in the same areas where migration may have occurred thousands of years ago, or has later migration and development of urban areas made these characteristics less obvious? It would be interesting to know how the frequencies of this gene have changed over time in certain areas, and then look at environmental/societal change to hypothesize why.
ReplyDeleteSuper interesting post! I can't wait to hear about upcoming research in this area. However, like Emily mentioned, I can't help but wonder if other factors such as migration and development may have also helped play a role in the appearance of these characteristics. And now, looking forward, would a mutation such as the one found in East Asians ever arise and become as characteristically defining in the closely tied world of today?
ReplyDelete