As anyone who has ever been to a Rice party can attest to, many of our friends from East Asian backgrounds tend to show a visible response to alcohol much more quickly than others might. While mostly thought of as nuisance, the pink facial tinting known as “Asian flush” or “Asian glow” is believed to have been evolutionarily selected as a favorable trait relatively recently in our biological history.
For those unfamiliar with “Asian flush,” the term is most commonly used to describe a wide range of symptoms that appear shortly after drinking alcohol. As the name implies, the most frequently experienced symptom of this is turning red in the face, though some report the occurrence of nausea, tachycardia, and facial swelling as well. These symptoms are produced as a direct result of an enzyme deficiency that leaves the body with an accumulation of one of alcohol metabolism’s first byproducts, acetaldehyde, which is the chemical culprit behind all of these unpleasant symptoms.
The polymorphism that produces this deficiency in aldehyde dehydrogenase 2 (ALDH2), (ADH1BArg47His), is found in nearly 50% of those of Asian decent, and in around 70% of those who are Han Chinese. Molecular dating techniques used in a recent study indicate that the emergence of this gene occurred approximately 10,000 years ago, around the same time as the dawn of agriculture and the first cultivation of rice in southern China. The authors of this study hypothesize that the widespread appearance of this gene could have been caused by the protective effect it confers, allowing people to enjoy the benefits of the alcohol that the development of agriculture made much more abundant, while forcing them to imbibe only in moderation. The emergence of “Asian flush” might actually be one of the most dramatic examples of how agriculture has affected human biology as well as our sociology.
So does “Asian glow” make some of your Asian friends more reproductively viable? Not exactly, though it should be thought of as a handy, “built in” reminder to pace oneself and drink responsibly.
-Caleb
Hsu, Jeremy. "Critics Say Cal's Genetic Tests Ignore 'Asian Flush' Risks." Live Science. 5 Aug. 2010. Web. 17 Apr. 2012. <http://www.livescience.com/8421-critics-cals-genetic-tests-ignore-asian-flush-risks.html>.
Peng, Yi, Hong Shi, Xue-bin Qi, Chun-jie Xiao, Hua Zhong, Run-lin Z. Ma, and Bing Su. "The ADH1B Arg47His Polymorphism in East Asian Populations and Expansion of Rice Domestication in History." BioMed Central. BMC Evolutionary Biology, 20 Jan. 2010. Web. 17 Apr. 2012. <http://www.biomedcentral.com/1471-2148/10/15/abstract>.
Rochman, Bonnie, Maia Szalavitz, and Alice Park. "Red-faced from Drinking? It Could Be an Evolutionary Advantage | Healthland | TIME.com." Time. 10 Jan. 2010. Web. 17 Apr. 2012. <http://healthland.time.com/2010/01/20/red-faced-from-drinking/>.
Wade, Nicholas. "Adventures in Very Recent Evolution." The New York Times. 19 July 2010. Web. 17 Apr. 2012. <http://www.nytimes.com/2010/07/20/science/20adapt.html?_r=2&ref=science>.
So, how do you think the positive association of the trait come about?
ReplyDeleteI ask because in our culture it seems as though having an Asian Flush is a sign of not being about to handle your drink (a decidedly negative trait today).
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ReplyDeleteMy theory on this is that in the first groups that began working agriculture in Asia, there may have been an outsized representation of the ALDH2 gene, and as readily-available food increased the fitness of the group, a founder population effect may have resulted from this that increased the frequency of the ALDH2 allele in the population. I don't feel like the 'protective mechanism' of having a flushed face would cause a significant change in fitness in a large population size just because of the likely non-presence of alcohol at that time, but it is an interesting explanation for the outsized presence of the gene.
ReplyDeleteWow, guys, these are all really cool theories! I think it's really interesting to think about how the fitness consequences of "holding your liquor" may have changed over time. The studies didn't really assert any hypotheses of how this gene became so widely spread, other than briefly describing the protective mechanism I mentioned. The way I imagined it, however, was that it may have emerged from the fitness cost that the effects of alcohol on development can sometimes incur, particularly when very young individuals consume it. From what I understand, alcohol likely did have a pretty widespread presence in ancient times not only as a drink, but as a way of preserving foods. I imagine that people were less stringent about children and young adults consuming alcohol as well, and I think a protective mechanism may very well have had an important at preventing fitness costs of alcohol consumption since it's something that would show a very immediate response. I'd be very excited to read more specific studies to find out more about this though.
ReplyDeleteCaleb