The latest neuroscience study of sex differences to hit the popular press has inspired some familiar headlines. The Independent, for example, proclaims that: “The hardwired difference between male and female brains could explain why men are ‘better at map reading’ (and why women are ‘better at remembering a conversation’).”
The study in question, published in Proceedings of the National Academy of Sciences, used a technology called diffusion tensor imaging to model the structural connectivity of the brains of nearly 1,000 young people, ranging in age from 8 to 22.
It reports greater connectivity within the hemispheres in males, but greater connectivity between the hemispheres in females. These findings, the authors conclude in their scientific paper, “suggest that male brains are structured to facilitate connectivity between perception and coordinated action, whereas female brains are designed to facilitate communication between analytical and intuitive processing modes.”
One important possibility the authors don’t consider is that their results have more to do with brain size than brain sex. Male brains are, on average, larger than females and a large brain is not simply a smaller brain scaled up.
Larger brains create different sorts of engineering problems and so—to minimize energy demands, wiring costs, and communication times—there may be physical reasons for different arrangements in differently sized brains. The results may reflect the different wiring solutions of larger versus smaller brains, rather than sex differences per se.
But also, popular references to women’s brains being designed for social skills and remembering conversations, or male brains for map reading, are utterly misleading.
In a larger earlier study (from which the participants of the PNAS study were a subset), the same research team compellingly demonstrated that the sex differences in the psychological skills they measured—executive control, memory, reasoning, spatial processing, sensorimotor skills, and social cognition—are almost all trivially small.
To give a sense of the huge overlap in behavior between males and females, of the 26 possible comparisons, 11 sex differences were either nonexistent or so small that if you were to select a boy and girl at random and compare their scores on a task, the “right” sex would be superior less than 53 percent of the time.
Even the much-vaunted female advantage in social cognition and male advantage in spatial processing were so modest that a randomly chosen boy would outscore a randomly chosen girl on social cognition—and the girl would outscore the boy on spatial processing—more than 40 percent of the time.
As for map-reading and remembering conversations, these weren’t measured at all.
Yet the authors describe these differences as “pronounced” and as reflecting “behavioral complementarity”—scientific jargon-speak for “men are from Mars, women are from Venus.” Rather than drawing on their impressively rich data-set to empirically test questions about how brain connectivity characteristics relate to behavior, the authors offer untested stereotype-based speculation. Even though, with such considerable overlap in male/female distributions, biological sex is a dismal guide to psychological ability.
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