A metanalysis of animal personality studies has punctured the widespread belief males are naturally more varied than females. In doing so, it greatly undermines pretty much the last biological explanation for men's predominance at the highest levels of science, business, and politics.
Since Darwin, biologists have believed male animals show more variation than females, attributing this to sexual selection. By extrapolation, it is claimed men are naturally more likely to occupy the extreme ends of the IQ spectrum. This provides a convenient explanation for male domination of many fields without conceding a glass ceiling.
However, if greater male variation is a consequence of biology, rather than society's sexism, then it should be found across an array of animals. Professor Michael Jennions of the Australian National University led a project to analyze variation in animal personality measurements. In Biological Reviews, Jennions and co-authors report the data simply isn't there to support the idea.
As Jennions said to IFLScience, “Darwin is almost never wrong.” Even in the last few years, several of Darwin's conclusions that remained controversial for a century have been vindicated. However, it seems he erred in making his 1871 claim that variation among males of a species is consistently larger than among females, which he attributed to the effects of sexual selection. It's been assumed to be true ever since. Curiously, pre-Darwin, it was female animals that were thought to be more variable.
"The idea that biology determines greater diversity of behavior among male than female animals is often used to explain why more men than women are considered geniuses or go on to become CEOs," said first author Lauren Harrison in a statement.
However, Jennions told IFLScience that “most of the features Darwin was talking about were ones that are really only expressed in males, like the peacock's tail, which makes it very hard to compare the variability.” For a fairer comparison, Jennions and Harrison looked at traits that occur in both males and females, such as boldness, aggression, and sociability.
There have been hundreds of studies on variability in animal personalities using measures such as hiding time (boldness) or numbers of interactions (sociability). The authors found 204 papers testing comparable traits for 220 species.
Contrary to their expectations, the authors found no evidence male animals are more varied in their personalities, even for measures such as aggression where sexual selection often raises the male baseline. The results were consistent whether they looked at mammals, fish, or invertebrates.
Jennions acknowledged to IFLScience humans might be the exception, but said in a statement that if so “this is likely caused by uniquely human factors”, which would be more credibly cultural than biological.
Havelock Ellis was the first to apply Darwin's variability claim to intelligence, proposing men had a wider range of brain sizes and therefore thinking capacity. In Ellis's day, this was an advance on the view men are more intelligent than women on average. As women's access to education has improved that's become harder to maintain – most people have met enough men who're pretty clearly not superior to anyone.
Ellis's hypothesis has filled the gap. Men can win most Nobel Prizes, the story goes, because they dominate both the smartest and the stupidest 1 percent. Nothing to do with sexual discrimination. The idea is particularly appealing to some men who are confident they are not at the bottom end of the spectrum, and therefore think they must be among the men superior to almost all women. Jennions warns against the Naturalistic Fallacy that equates natural with good, but men wanting to claim superiority need to look further.