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“Two Minds” two years later: Still curious about sex differences in cognition? Here are some resources

A Stanford Medicine magazine article on sex differences in the brain remains popular; this article provides additional information.

I wrote "Two Minds: The cognitive differences between men and women," for the spring 2017 issue of our magazine, Stanford Medicine. Just over two years later, it's been one of our most popular pieces.

I still get a steady stream of emails about this article; this is clearly a topic of enduring interest. "Two Minds" casts neither sex as intellectually or emotionally inferior; it outlines evidence indicating that brain differences between males and females contribute to differences in behavior and cognition.

From a purely evolutionary standpoint, one would expect to see those differences. As I wrote in a recent blog post about new research by Stanford neurobiologist Nirao Shah, PhD, a key source for "Two Minds" :

Having co-evolved for hundreds of millions of years, the two sexes have acquired differing reproductive strategies, with resulting divergent yet complementary behaviors. After all, why would evolution come to a screeching halt above the neck?

In researching "Two Minds," I read scores of studies and reviews and spent hours talking with experts. Space doesn't permit me to repeat all of the sex-associated behavioral differences that have been identified in mammalian (including human) behavior or their physiological or anatomical underpinnings, many of which are listed in "Two Minds." But here's a sprinkling of background documentation concerning a few of the article's main points.

Granted, cats and rats and monkeys and mice aren't people -- but abundant animal research demonstrates hardwired sex differences in mammalian behavior. Repeated studies, for instance, indicate male rhesus monkeys strongly prefer toys with wheels over plush toys, whereas females find plush toys likable. We know that the monkeys' parents didn't buy them sex-typed toys or encourage their male offspring to play more with trucks. In humans, similar differences emerge early enough in life to suggest some degree of biological causation. 

Variations on this theme persist through adulthood, and across numerous diverse cultures. Recent studies such as this one are beginning to explain the neurobiology behind what the literature has long reported: On average, women are more people-oriented. Many men are more thing-oriented.

What biological influence within individuals, independent of very real social influences, might initiate and drive the two sexes' demonstrated divergence in abilities and preferences? There's still much to sort out, but hormones are surely a big part of it. 

Numerous studies, in animals and humans alike, about prenatal hormonal exposure indicate that our brain's fates are altered profoundly and permanently by punctuated surges in these hormones' levels -- particularly testosterone -- or the lack of such surges at critical points during development. (Examples include this decades-spanning examination of gendered adult behavior, reported in 2000; this one about sex-differentiated child behavior; this one about adult occupational interest; this one about brain structure; and this one about exposure to xenoestrogens).

Men are not from Mars, nor women from Venus. But here on Earth, although we're mostly the same, we're slightly different. And our cognitive sex differences have evidently served us well evolutionarily for the vast bulk of human existence. The thing is, technological and societal developments in the past few hundred years have rendered many of those differences obsolete and have shrunk the significance of physical differences between the sexes.

Yet we're still cruising around inside those vestigial vehicles known as our bodies, which adapt only at a snail's pace relative to the rapidity of recent technological and societal progress. Inasmuch as our brains are every bit as much flesh and blood as the rest of us is, we still retain hints of our sex-stamped evolutionary heritage. The better we understand them and their interactions with modern social influences, the better we'll be able to shape our future.

Photo by MonicaVolpin

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