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Be Wary of Studies That Claim Men and Women's Brains Are Wired Differently


The Wall Street Journal reported this week on a spate of controversial new studies suggesting behavioral differences between men and women are due to “hard-wiring” in the brain. In the most comprehensive study, published this month in the journal Proceedings of the National Academy of Sciences, biomedical scientists at the University of Pennsylvania compared brain images of nearly 1,000 men and women aged 8 to 22 and found that the connective tissues between the two hemispheres developed differently in men and women, particularly during adolescence—with significant behavioral consequences.

Women are mostly better connected left-to-right and right-to-left across the two brain hemispheres…Men are better connected within each hemisphere and from back-to-front. That suggests women might be better wired for multitasking and analytical thought, which require coordination of activity in both hemispheres. Men, in turn, may be better wired for more-focused tasks that require attention to one thing a time. But the researchers cautioned such conclusions are speculative.

The study has, unsurprisingly, attracted plenty of criticism—some of it informed, some of it less so. We shouldn’t ignore research whose implications we don’t like—but that seems to be the premise of one camp of critics, who call the study “too depressing to blog about” or claim that the researchers “threw a wet blanket on gender equality.” More convincing rebuttals come from scientists like Christian Jarrett, who argues that the researchers exaggerated the statistical significance of the differences between the male and female brains, and Cordelia Fine, author of Delusions of Gender, who suggests the differences the researchers identified might have more to do with differences in brain size than function.

The thing about these studies is that unless you’re a neuroscientist, you’re probably just going to find an interpretation that reinforces your original belief. If you’re the Daily Mail, the takeaway is that “Men’s brains…are better at concentrating on single complex tasks—whether it be reading a map or cooking a meal.” If you’re Salon, you’re panicking that this study will “lock women in the kitchen and men in the lab.” Whichever camp you subscribe to, you can find something to support and refute your argument in these debates over whether gender differences are hard-wired. Consider the following studies:

Do high fetal testosterone levels make females more empathetic?

A group of Cambridge scientists led by Simon Baron-Cohen has argued that men are, on average, more suited to tasks that require “systemizing”, while women are better at “empathizing.” “Systemizing” refers to the drive to analyze, explore and construct a system, while “empathizing” involves identifying others’ emotions and thoughts and responding to them appropriately. Baron-Cohen analyzed the fetal testosterone levels of hundreds of male and female fetuses, based on the amniotic fluid of their mothers, and compared it to measures of the children’s empathizing or systemizing abilities. He found an inverse correlation between FT levels and measures of empathy at different stages of development—for instance, frequency of making eye contact with researchers at 12 months, size of vocabulary at 24 months and ability to interpret others’ emotions based on their eyes at age eight.

Seems convincing—but different researchers get different results. One study found that seven-year-old boys’ performance on a mental rotation—a measure of spatial reasoning or “systemizing”—was not correlated with fetal testosterone levels. Another study found that four-year-old children’s abilities to copy a block structure, count and sort did not increase with levels of amniotic testosterone—and for girls, it actually decreased.

Do male newborns' interest in mobiles mean they're wired for systemizing?

If you want to figure out whether something is hardwired, testing unsocialized babies is your best bet. Jennifer Connellan, a student of Baron-Cohen, presented a hundred newborns with two stimuli: a mobile (to represent an interest in systems) or her own face (a stand-in for an interest in empathy) and filmed the babies’ responses. When she and her team analyzed the videos, they found that the male babies spent more time looking at the mobile than did the females, while all the babies spent about the same amount of time looking at her face.

When two psychologists with a different agenda repeated the experiment, they got correspondingly different results. Leeb and Rejskind conducted the same studywith a few tweaks—most importantly, ensuring that the experimenters would not know the sex of the babies. (For example, they dressed the babies in gender-neutral outfits and separated the babies from their mothers to minimize the risk that the experimenters would hear the babies’ names.) In this study, no gender differences were found in the amount of time the newborns spent looking at each stimulus—though gender differences did exist in the follow-up study three to four months later. They conclude that “experimenter expectancy effects” can explain the differences Connellan found; perhaps she unconsciously opened her eyes wider and engaged the baby more when it was female.

Does the size of one part of the brain mean that women are better at nurturing?

One study by researchers at the University of Iowa, found that the straight gyrus (SG), an area of the brain thought to be related to social cognition and interpersonal awareness, was proportionally larger in adult women than in adult men. They also found a correlation between SG size in both men and women and scores on a widely used test of social cognition, from which they concluded that women, perhaps because of their role in child-bearing, are naturally better-suited to nurturing.

But when the same team carried out the same experiment on children, they ended up poking a hole in their own theory: They found that, in children, the SG was actually proportionally larger in boys than girls—and that, for children, the same test of social cognition was inversely correlated with SG size.