The illusion of a universe in our own back yard

Science News covers a revealing new study on the Hadza people of Tanzania that has the potential shake up some of the rusty thinking in evolutionary psychology.

A common line of argument in this field is to suggest that sexual preferences for certain body types exist because we’ve evolved these desires to maximise our chances of mating with the most fertile or healthiest partner.

For example, studies have interpreted the fact that taller men are more likely to attract mates and reproduce in terms of evolutionary pressures on sexual desire. But most of these and similar studies have been completed on Western samples, while the authors draw conclusions about the ‘universal’ nature of these ‘evolutionary’ pressures.

To test how universal these body preferences really are, anthropologists Rebecca Sear and Frank Marlowe looked at whether similar preferences existed in the Hadza people, a hunter-gather tribe from Tanzania.

It turns out, these supposedly ‘universal preferences’ don’t exist in the Hadza. You can read the full text of the paper online as a pdf, but this is taken from the Science News write-up:

Hadza marriages don’t tend to consist of individuals with similar heights, weights, body mass indexes, body-fat percentages or grip strengths… Neither do Hadza couples feature a disproportionate percentage of husbands taller than their wives, as has been documented in some Western nations, the researchers report in the Oct. 23 Biology Letters.

Almost no Hadza individuals mention height or size when asked to explain what makes for an attractive mate, Sear and Marlowe add.

People everywhere seek healthy, fertile marriage partners, Sear proposes. “But I suspect there may not be a preference for one particular signal of health in mates across every population,” she says….

Sear and Marlowe criticize evolutionary psychologists who have argued that physical size influences mating decisions in all societies. That argument rests largely on self-reports of Western college students and analyses of personal advertisements in U.S. newspapers for dating partners, they say.

The problems with relying on Western college students as participants in psychology studies is also addressed by a new paper just released by Behavioural and Brain Sciences which you can read online as a pdf.

The article reviews data from psychology experiments and argues that not only are college students a very restricted subset of society, but they are actually wildly atypical in comparison to the rest of the world’s population.

In fact, the authors state that “The findings suggest that members of WEIRD [Western, Educated, Industrialized, Rich and Democratic] societies, including young children, are among the least representative populations one could find for generalizing about humans”.

Link to Science News on Hadza study.
pdf of scientific paper on mating selection in the Hadza.
pdf of BBS article on WEIRD people and selection bias (thanks Tom!)