Chinese, Japanese and Europeans, meanwhile, have all seen changes in a serotonin transporter.

ECONOMIST: Human evolution

The serotonin-transporter gene comes in two functional variants long and short.

ECONOMIST: The genetics of happiness

That some populations have more of the long version of the serotonin-transporter gene has been noticed before, though the association has previously been made at a national, rather than a racial, level.

ECONOMIST: The genetics of happiness