If you’ve spent any time in Japan you will have heard the expression, “Deru kugi wa utareru” (“The nail that sticks out gets hammered down”). The phrase is used to explain how Japanese society traditionally prefers conformity and social harmony to independence and individual expression. There is a similar saying in China — “The shot hits the bird that pokes its head out” — and no doubt something equivalent in South Korea, too. East Asian countries tend to have collectivist societies, while individualism typically prevails in the West.

Over the years, if I wondered at all why East and West were different in this way I think I’ve put it down to something to do with the fact that the societies were steeped in values from Confucianism and Christianity, respectively. I didn’t think about any underlying evolutionary reason, probably because I thought culture and politics were more powerful, and quicker, at shaping high-level things such as societal structure.

But Joan Chiao, a psychologist at Northwestern University in Evanston, Illinois, has thought a lot about it, and she has put together a fascinating idea: It comes down to a short chunk of DNA that we all have in varying amounts.

The chunk is found in the serotonin-transporter gene on chromosome 17. You’ll have heard of serotonin, a chemical commonly associated with feelings of happiness. We tend to feel happier when there is more serotonin in the bloodstream, which is why stopping it from being mopped up by using drugs such as Prozac can benefit people suffering from depression. The serotonin-transporter gene’s job is to make a protein that carries serotonin away to be recycled.

As in most genes, there’s a region of the serotonin-transporter that controls how much of the gene product is made. It controls the expression of the gene, which is like saying it’s the tap regulating water flow into a bath. In 1994, geneticists discovered that this region, 5-HTTLPR, occurs in two forms: a long and short form. People who posses the long form make more of the product than the short form, and more of the transporter product means less serotonin is left in the system compared with people with the short form. This discovery immediately had the neuroscientists and psychiatrists wondering: What would the behavioral effect of this difference be in people?

In 2003, a bombshell paper in the journal Science suggested an answer. A small study of young men and women in Dunedin, New Zealand, found that people with the short form of the gene were more prone to depression, and even suicide, than people with the long form. People with the long form, in contrast, tend to be naturally happier people.

Hundreds of research papers have since attempted to delve into the apparent effect of the 5-HTTLPR gene, but the results have not led to a clear answer. To study the genetics of such complex traits as happiness and depression requires huge sample sizes, and researchers simply haven’t had enough people to examine.

Chiao knew that the short form of 5-HTTLPR occurs at a higher frequency in East Asia than it does in, say, Europe. The short form, remember, is the one linked to depression, while the long form is associated with greater reported well-being. Could these genetic differences between East and West form the basis of cultural differences in individualism and collectivism? She teamed up with colleague Katherine Blizinsky, who is also from Northwestern, to examine the idea.

The pair gathered data on 5-HTTLPR from 50,135 people in 29 countries, including Germany, the U.K. and U.S., Japan, China and South Korea. They compared this with other data from those countries, such as cultural values, economics and disease prevalence.

They found that collectivist cultures were much more likely to contain people with the short form of 5-HTTLPR. The relationship held even when they controlled for economic and health factors.

The results were published in the journal Proceedings of the Royal Society of London, B. In a typical sample of people from East Asia, 70-80 percent of people have the short form of 5-HTTLPR while the percentage for a typical European sample is 40-45 percent. “Collectivism,” the pair wrote, “serves an ‘anti-psychopathology’ function.”

In other words, collectivist societies supposedly reduce the amount of psychological pressure people feel. They do this by lowering the amount of individual stress people feel, because society spreads out the stress rather than loading it up.

No one is saying that differences in 5-HTTLPR caused Japan to become collectivist. But the apparent finding of differences in the frequency of the two forms between East and West serves as a useful reminder that societies are complex things. Chiao and Blizinsky say a complete understanding of the factors that contribute to societal structure requires us to look at genetics, as well as the usual social and environmental factors.

Natural Selections covers issues related to scientific research in Japan on the fourth Saturday of the month. Rowan Hooper is the news editor of New Scientist magazine. Follow him on Twitter @rowhoop.

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