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The Science of Sex Differences

Matt Fradd

More and more people in our nation today think that sex (that is, maleness and femaleness) is not an objective biological reality but rather a social construct. Accordingly, instead of “sex” they prefer to use the word “gender”—a word that, until late last century, referred exclusively to language (most languages apart from English assign male, female, or neuter genders to nouns). Unlike sex, gender can be manipulated to serve cultural preferences.

Though there are a variety of ways to respond to this nonsense (how’s that for tipping my hand?), in this post I would like to respond with some findings of modern science.

Those who reject the objectivity of sex will often say that although male and female bodies may have some differences between them, our brains are just the same. One man, who is currently raising three “genderless children,” argued, “If you really want to get to know someone, you don’t ask what’s between their legs.”

But is the only difference between men and women “what’s between their legs”?

Brain Differences

As it turns out, male and female brains are biologically different.

in 2004, an all-star team of fourteen neuroscientists, from the University of California, the University of Michigan, and Stanford University, published findings showing that male brains are genetically programmed to be different from women’s.

These scientists analyzed thirty samples of human brain tissue taken from different sections of the brain and from different individuals. They were not told the sex of the individual from whom each specimen was taken, and simply by genetic analysis of the brain tissue they were able to correctly identify the sex of every sample.

Neuroscientist Larry Cahill, in an article for Scientific American, wrote that the structural, chemical, and functional differences between the brains of males and females raise the possibility of developing “sex-specific treatments” for conditions such as depression and schizophrenia.


The differences between male and female brains affect many aspects of behavior and perception, including memory, emotion, vision, hearing, how we handle stress—and even the toys we like to play with.

Researchers (and parents) have noted boys are more likely to play with balls and cars, whereas girls tend to prefer dolls and Easy-Bake ovens.

Those who claim that “gender” is a social construct find this abhorrent. Earlier this year, Boots, the largest pharmacy chain in the U.K., felt compelled to take down the signs for “boys” and “girls” toys after shoppers took to Facebook and Twitter to accuse the retailer of “sexist behavior.” Meanwhile, in Sweden they’ve begun pushing “gender-blind” toy catalogs picturing girls shooting toy guns and boys blow-drying hair.

Although it flies in the face of political correctness, science strongly suggests that the reason boys and girls prefer to play with different toys has less to do with cultural conditioning than with brain biology.

In 2002, Melissa Hines of City University London and Gerianne M. Alexander of Texas A&M University decided to conduct experiments on vervet monkeys, one of our closest biological cousins. They found that the monkeys showed “sex differences in toy preferences similar to those documented previously in children.” The boy monkeys typically preferred playing with cars and balls, while the female monkeys preferred playing with dolls and pots. (And they didn’t have parents or toy catalogs telling them which they should prefer.)

They concluded that such “sexually dimorphic preferences” for certain features in objects are deeply embedded products of evolution, preferences related to the very nature of being male or female—preferences that human children also clearly exhibit.

All that differentiates men and women is what’s “between their legs”? Far from it.

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