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

ECONOMIST: Human evolution

One of the researchers, Jan-Emmanuel De Neve, of University College, London, and the London School of Economics, has tried to do just that, by picking a popular suspect the gene that encodes the serotonin-transporter protein, a molecule that shuffles a brain messenger called serotonin through cell membranes and examining how variants of that gene affect levels of happiness.

ECONOMIST: The genetics of happiness

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