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Man is a rational animal – so at least I have been told. Throughout a long life, I have looked diligently for evidence in favour of this statement, but so far I have not had the good fortune to come across it, though I have searched in many countries spread over three continents.

Man is a rational animal – so at least I have been told. Throughout a long life, I have looked diligently for evidence in favour of this statement, but so far I have not had the good fortune to come across it, though I have searched in many countries spread over three continents.

So wrote Bertrand Russell in 1950. The idea of rational man, or homo economicus, (that people weigh up the economic costs and benefits of each choice open to them and choose the one that maximises their gain) has been widely debunked by a series of peer-reviewed papers and popular books by behavioural scientists.

But one criticism of this emerging field is that many of the studies used to support the debunking – of experiments in which people making seemingly irrational choices – tend to involve similar samples of people. A trio of behavioural scientists from the University of British Columbia report that 96 percent of subjects in the top psychology journals came from western industrialised countries; Western, Educated, Industrialized, Rich and Democratic societies as they dub them. But the results of these studies are too often assumed to be universally applicable.

The researchers continue to review a number of studies in which the behavioural quirks and biases investigated are compared across cultures. One of these is a visual perception bias, illustrated by the well known Müller-Lyer illusion, in which lines appear to differ in length according to arrows or tails placed on the lines.

Müller-Lyer illusion

It turns out that the effect of the “illusion” is much reduced for non-WEIRD people; it has virtually no effect on the San Foragers of the Kalahari for example. But the cohort of people from the States were the most powerfully affected by the illusion.

As the paper concludes; “Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions of human nature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity”.

Perhaps Bertrand Russell should have gone to the Kalahari Desert in his quest for rationality.

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