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Inside the heads of men and women: A look at sex-based cognitive differences

I first began ruminating on what would eventually become my just-published Stanford Medicine magazine article, "Two Minds: The Cognitive Differences between Men and Women," in 2013, when I attended an on-campus symposium on the question of whether any such differences exist.

Numerous interviews and seminars and many dozens of slowly digested research reports later, the answer is clear. An excerpt from the article:

Scientists routinely acknowledge that the presence or absence of a single DNA base pair can make a medically important difference. What about an entire chromosome? While the genes hosted on the X chromosome and the Y chromosome (about 1,500 on the X, 27 on the Y) may once have had counterparts on the other, that’s now the case for only a few of them. Every cell in a man’s body (including his brain) has a slightly different set of functioning ​sex-​chromosome genes from those operating in a woman’s.

So it shouldn't be surprising that, over the past 15 years or so, new technologies and new hypotheses have generated a growing pile of evidence that there are inherent differences in how men’s and women’s brains are wired and how they work.

And even -- at least to some degree -- in what men and women want. Findings along these lines from animal and human studies alike continue to accrue. Again, from the article:

In a study of 34 rhesus monkeys, for example, males strongly preferred toys with wheels over plush toys, whereas females found plush toys likable. It would be tough to argue that the monkeys’ parents bought them sex-typed toys or that simian society encourages its male offspring to play more with trucks. ... [In a very recent study,] boys and girls 9 to 17 months old — an age when children show few if any signs of recognizing either their own or other children’s sex — nonetheless show marked differences in their preference for stereotypically male versus stereotypically female toys.

Nor do men and women's differences stop at the borders of normal cognition and behavior. Quite the contrary:

Women are twice as likely as men to experience clinical depression in their lifetimes; likewise for post-traumatic stress disorder. Men are twice as likely to become alcoholic or drug-dependent, and 40 percent more likely to develop schizophrenia. Boys’ dyslexia rate is perhaps 10 times that of girls, and they’re four or five times as likely to get a diagnosis of autism spectrum disorder.

It now seems that in utero sex-hormone bursts, which permanently affect the brain's structure and function, may differentially predispose men and women to these mental disorders.

At the 2013 event I alluded to earlier, a featured speaker whose talk particularly grabbed my attention was molecular psychiatrist Nirao Shah, MD, PhD. At the time, Shah was situated at the University of California, San Francisco. These days he's at Stanford, and he proved to be a key source for my article.

Trying to assign exact percentages to the relative contributions of “culture” versus “biology” to the behavior of free-living human individuals in a complex social environment is tough at best. But it's safe to say the role of culture is not zero. The role of biology is not zero, either.

Previously: Stanford Medicine magazine reports on sex, gender and medicineTomayto, tomahto: Separate genes exert control over differential male and female behaviors, Men's typically taciturn Y chromosomes tell colorful tale of conquests, expansions and Having a copy of ApoE4 gene variant doubles Alzheimer's risk for women but not for men
Illustration by Gérard DuBois

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