Lots of people get flushed in the face when they feel embarrassed, but for many Asians it’s the facial flush itself that can be embarrassing.
About half of all people of Asian descent share a genetic trait that causes a prompt reddening of the face in response to drinking alcohol — the result of an enzyme deficiency that interferes with alcohol metabolism and causes the temporary build-up in the body of a toxic chemical product. For some, the red face is a mere nuisance; for others, it can be accompanied by symptoms such as rapid heartbeat and skin swelling. Talk about a buzz-kill.
Now researchers speculate about why East Asians have the flushing gene in the first place. According to a new study in BMC Evolutionary Biology, the genetic mutation that causes the reaction first appeared about 10,000 years ago in Southern China, at about the same time residents began farming rice along the Yangtze River. The study’s authors hypothesize that the alcohol intolerance associated with facial flushing may have evolved as a survival strategy enabling ancient populations to enjoy the positive effects of alcohol derived from fermented rice — it can be used as a disinfectant and preservative — while imbibing in moderation. “This is one of the few cases reported demonstrating the genetic adaptation of human populations to the dramatic changes in agriculture and diet during Neolithic times,” said Bing Su, one of the study’s co-authors from the Chinese Academy of Sciences, in a press release about the study.
By sampling DNA from 38 distinct Asian populations from relatively isolated provincial areas, ranging from Han Chinese to Tibetans, researchers observed that the flushing gene was much more prevalent in groups that began farming rice the earliest. For example, while the mutation appears in nearly 70% of Han Chinese, who began farming rice 7,000 to 10,000 years ago, it shows up in only 14% of Tibetans, whose rice culture developed later. Molecular dating of rice found in ancient pottery has enabled anthropologists to determine when rice farming began in different regions of the continent.
While the red-faced alcohol response can be annoying, it may also be beneficial to populations on the whole, as it appears to be associated with lower rates of alcoholism. In fact, the drug disulfiram, which is used to prevent relapse in recovering alcoholics, has some of the same biochemical effects as the flushing gene does when it is expressed.