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Why are Asians drank face is easy to red? Recently, Chinese Academy of Sciences of Kunming Institute of Zoology research team led by Bing Su published research papers in the "BMC Evolutionary Biology" , pointed out that "drinking blush" It may be related to rice cultivation. They believe that the era of domesticated crops such as rice in China has led to changes in the structure of human food and then led to a certain gene mutation, making easy for the so-called "Asian red."

When you drink, enzymes in the liver known as alcohol dehydrogenases (ADHs) convert alcohol to an organic compound called acetaldehyde; another enzyme then converts acetaldehyde to acetic acid. But about 50% of Asians and 5% of Europeans have mutations in these enzymes that can increase the rate of alcohol metabolism up to 100-fold. This leads to a rapid accumulation of acetaldehyde, which can cause capillaries in the face to dilate�–and the face to turn red. Other unpleasant symptoms can include nausea and headaches. In 2008, a team led by geneticist Kenneth Kidd of Yale University found that one of these mutations–known as ADH1B*47His–may have been favored by natural selection in many East Asian populations.

The researchers searched for the ADH1B*47His mutation in 2275 people across China representing 38 ethnic groups. They found that it was highly prevalent, up to 99%, in ethnic groups from southeast China; a bit less prevalent, 60% to 70%, in western China; and relatively uncommon, 14%, among Tibetans. Moreover, the team found a strong geographical correlation between regions with a high prevalence of the mutation and archaeological sites in China where rice had been domesticated thousands of years ago.

When Su and his colleagues calculated the age of the mutation, it came out at between 7000 and 10,000 years ago. That corresponds roughly to the earliest known evidence for rice farming, the team reports online this week in BMC Evolutionary Biology. "The [mutation] rose to extremely high frequency in a relatively short time, implying that the selective force was quite strong," Su says.

As for what the selective pressure was, the team concludes that the mutation was favored because it protected early farmers from the potentially fatal harms of drinking too much. The researchers cite two additional pieces of evidence for this hypothesis. First, recent archaeological evidence suggests that Chinese farmers concocted an alcoholic brew of rice, honey, and grape or hawthorn as early as 9000 years ago. Second, the drug disulfiram, which causes acetaldehyde to accumulate in the body, discourages alcoholics from drinking by causing nausea, vomiting, and other severe alcohol flush reaction symptoms.

This study is the latest in a growing body of research showing just how important human culture has been as a transformational force in human evolution," says Darren Curnoe, an anthropologist at the University of New South Wales in Sydney, Australia. Indeed, the rise of farming has been linked to evolutionary changes in genes for other enzymes, such as amylase, which breaks down starch, and lactase, which breaks down lactose in milk.

Other researchers are not entirely convinced. Kidd says that the hypothesis is "quite reasonable" but that it’s still speculation at this point. He also questions whether the team has determined the age of the mutation correctly, because the estimates range over at least 3000 years. And Dorian Fuller, an archaeologist at University College London, argues that the team may be wrong to pin the mutation’s origins solely on rice cultivation. The archaeological sites the researchers chose, he says, included settlements where rice had just begun to be farmed and those where rice farming was in full flower. Fuller adds that if the team had restricted its analysis to those later sites where rice had become a predominant crop, beginning about 8000 years ago, then alcoholic beverages could also have been made from grapes–and rice might not be solely responsible for the Asian Flush.

The ADH1B Arg47His polymorphism in East Asian populations and expansion of rice domestication in history

Yi Peng, Hong Shi, Xue-bin Qi, Chun-jie Xiao, Hua Zhong, Run-lin Z Ma  and Bing Su

BMC Evolutionary Biology 2010, 10:15 doi:10.1186/1471-2148-10-15

Abstract

Background

The emergence of agriculture about 10,000 years ago marks a dramatic change in human evolutionary history. The diet shift in agriculture societies might have a great impact on the genetic makeup of Neolithic human populations. The regionally restricted enrichment of the class I alcohol dehydrogenase sequence polymorphism (ADH1BArg47His) in southern China and the adjacent areas suggests Darwinian positive selection on this genetic locus during Neolithic time though the driving force is yet to be disclosed.

Results

We studied a total of 38 populations (2,275 individuals) including Han Chinese, Tibetan and other ethnic populations across China. The geographic distribution of the ADH1B*47His allele in these populations indicates a clear east-to-west cline, and it is dominant in south-eastern populations but rare in Tibetan populations. The molecular dating suggests that the emergence of the ADH1B*47His allele occurred about 10,000~7,000 years ago.

Conclusion

We present genetic evidence of selection on the ADH1BArg47His polymorphism caused by the emergence and expansion of rice domestication in East Asia. The geographic distribution of the ADH1B*47His allele in East Asia is consistent with the unearthed culture relic sites of rice domestication in China. The estimated origin time of ADH1B*47His allele in those populations coincides with the time of origin and expansion of Neolithic agriculture in southern China.