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.