The Meaning of Sexual Differences 


"I teach a course on 'Philosophy of Human Sexuality,' and I must have read fifty to a hundred books on the topic. On the Meaning of Sex is, quite simply, number one, especially for this generation. It is deep yet clear, reverent yet punchy, sound yet relevant, idealistic yet realistic, thoughtful yet exciting. It makes boredom impossible. The style is as beautiful as the content." - Peter Kreeft

All they who serve are telling me
Of Your unnumbered graces;
And all wound me more and more,
And something leaves me dying,
I know not what, of which they are darkly speaking.

— John of the Cross, Spiritual Canticle

How many more colors there are in the world because there are two sexes and not just one! How amusing they are to each other, and yet how baffling! Mutual perplexity can be part of the fun, a fountain of mirth, making the shimmering hues of strangeness sparkle all the more. In our day, though, perplexity isn't so amusing; it has an edge to it. We see all those colors all right, but admitting to the sight is considered shameful and offensive. Just as some ages have held it loutish to work with one's hands, so our time holds it crude to make use of one's eyes. So we make ourselves a little blind. We squint, throw dust in our eyes, and try not to look at things straight on.

A well-socialized young woman whom we may call Carissa had been reading some of the classics for the first time. One day when we were talking, she asked a question which all well-socialized young women who are reading the classics for the first time are expected to ask these days. Why did those bygone writers speak as though men and women are different?

"Maybe because they are different," I said. "Don't you think so?"

Plainly annoyed by my answer, she demanded, "Weren't those old views just prejudices?"

"Well, it's not easy to disentangle the prejudices of one's own time and place from universal truth. Maybe none of those writers did disentangle them perfectly. Still," I said, "aren't certain differences between men and women acknowledged everywhere?"

"But men and women aren't different."

"Then why do you think every culture supposes that they are?"

"Oh, I know the sexes end up different everywhere," she said. "But that only happens because boys are raised differently than girls."

"Let me be sure I follow you. You don't deny that some sex differences are universal — "


" — but you say they aren't natural. The only reason for them is differences in how boys and girls are brought up."

"That's right."

"Let's think about that. To produce the same differences between boys and girls everywhere, those differences in upbringing would also have to be the same everywhere, wouldn't they?"

On the Meaning of Sex
by J. Budziszewski

"Yes. Boys are always raised differently than girls."

"And yet you think these differences in upbringing have no basis in human nature."

"Right, because they don't."

"If they have no basis in human nature, then why are they universal?"

"What do you mean?"

"If they are merely arbitrary, wouldn't you expect them to vary from culture to culture?"

"No, because cultures influence each other."

"You mean cultures that raise boys and girls differently influence other cultures to raise them differently?"

"Of course."

"Why shouldn't it be the other way around? If it's all because of culture, then why don't some cultures raise boys and girls the same, and influence other cultures to follow them?"

"I don't understand you."

"To put the question another way," I asked, "if the pattern of upbringing has no basis in human nature, then why is it so persistent?"

Carissa dodged the question, instead protesting an opinion I hadn't expressed. "Aren't men and women equally human?"

"Equally human, sure, but not the same. Complementary variations on the same musical theme. Different voices singing in polyphony."

"Tell me one fundamental difference between men and women," she demanded.

"That's easy. I could never bear a child. A woman can."

"Not all women. Aren't some women infertile?"

"Sure, but you're confusing essence with accident," I said. "A fertile woman can bear a child, but not even a fertile man can pull off a feat like that."

By now Carissa was thoroughly exasperated. Hurling down her trump card, she exclaimed, "I know men's and women's bodies are different, but in their brains they're just the same."

The details fade from memory, so I may have slightly misquoted some of Carissa's words. Not the words of her final sentence, which have echoed in my mind ever since. This chapter is not about brain science. Nonetheless, let us pause to consider what is known about men's and women's brains.

Cahill says that "the picture of brain organization that emerges is of two complex mosaics — one male and one female — that are similar in many respects but very different in others.

"In their brains," it turns out, men and women are different after all. According to neuroscientist Larry Cahill, the differences are marked, pervasive, and consistent.[1] The cliché that variation within each sex is greater than variation between the sexes is simply false. Moreover, the contrasts between men and women are evident not just in a few extreme cases, but across the whole distribution, and they involve not only the activity of the brain, but also its organization and development. Doreen Kimura, another brain scientist, remarks that although environment certainly influences us, the differences in brain organization occur "so early in life that from the start the environment is acting on differently wired brains in boys and girls."[2]

How many are these differences in wiring? Legion. To mention just a few: Large parts of the brain cortex are thicker in women than in men. Ratios of gray to white matter vary, too. The hippocampus, which plays a role in memory and spatial navigation, takes up a greater proportion of the female brain than of the male brain. On the other hand, the CA1 region of the hippocampus is larger in the male. A variety of neurotransmitter systems work differently in men and women; neurotransmitters are the chemicals that carry nerve impulses across the synapses. Sex hormones, obviously different in men and women, influence not only the excitability of hippocampus cells, but also various aspects of their structure. The right and left hemispheres are more interconnected in female brains than in male ones, and the corpus callosum, which links them together, is larger. The amygdala, involved in emotion and emotional memory, is larger in men, but the deep limbic system, which is also involved in emotion, is larger in women. Across a spectrum of different functions, which side of the amygdala controls which function is reversed in men and women. Sex-related differences between the hemispheres exist for other brain regions as well, including the prefrontal cortex, involved in personality, cognition, and other executive functions, and the hypothalamus, which links the nervous system with the endocrine system and has some connection with maternal behavior. External circumstances, such as chronic stress, act on male brains differently than on female. Brain diseases also diverge in men and women, not only in their frequency, but in their age of onset, duration, and the way they manifest themselves. Even the neurological aspects of addiction differ between the two sexes.

Although not all neurological differences are associated with behavioral differences, the differences between male and female brains affect numerous aspects of behavior, including "emotion, memory, vision, hearing, processing faces, pain perception, navigation, neurotransmitter levels, stress hormone action on the brain, and disease." Cahill says that "the picture of brain organization that emerges is of two complex mosaics — one male and one female — that are similar in many respects but very different in others. The way that information is processed through the two mosaics, and the behaviors that each produce, could be identical or strikingly different, depending on a host of parameters." He concludes with a quotation from a report of the medical branch of the National Academy of Sciences: "Sex does matter. It matters in ways that we did not expect. Undoubtedly, it matters in ways that we have not yet begun to imagine."[3]

So Carissa had it exactly backwards. It seems that our brains are even more different than the rest of our bodies. Why is it so hard even to discuss the differences between the sexes? I think because we miss four large truths.

One of these large truths might be called the duality of nature. Manhood and womanhood reflect the same human nature, and with equal fidelity and dignity, but they reflect different facets of it. There are two ways to get this matter wrong. One way is to think that because the two sexes are different, they must be unequally valuable — woman an inferior version of man, or man an inferior version of woman. The other way is to think that because the sexes do have equal worth, they must be exactly the same.

Another large truth is the duality of path. The developmental trajectories of men and women are different at both ends — not only in what they start with, the susceptibilities and tendencies that each sex must discipline and prune, but in what they end with, what each sex ripens into when all goes as it should. Some people miss the point by ignoring the difference in starting points, as though the difference between the raw materials from which maturity is built were unimportant. That is like thinking that a house can float above its foundations.


  1. Larry Cahill, "Why Sex Matters for Neuroscience," Nature Reviews: Neuroscience 7 (2006), 477-84. See also Larry Cahill, "His Brain, Her Brain," Scientific American 292, no. 5 (2005): 40-47.
  2. Doreen Kimura, "Sex Differences in the Brain," Scientific American 267, no. 3 (1992): 119-25.
  3. Cahill, "Why Sex Matters for Neuroscience."




J. Budziszewski. "The Meaning of Sexual Differences." from On the Meaning of Sex (Downer's Grove, IL: Intercollegiate Studies Institute, 2012): 35-40.

Reprinted with permission from the author and the Intercollegiate Studies Institute. All rights reserved.


J. Budziszewski (Boojee-shefski) earned his doctorate from Yale University in 1981. He teaches at the University of Texas in Austin, in the Departments of Government and Philosophy where he specializes in the relations among ethical theory, political theory, and Christian theology. The focus of his current research is natural law and moral self deception. J. Budziszewski is a former atheist, former political radical, former shipyard welder, and former lots of other things, including former young and former thin. He's been married for more than thirty years to his high school sweetheart, Sandra, and has two daughters. He loves teaching. He says he also loves contemporary music, but it turns out that he means "the contemporaries of Johann Sebastian Bach." He deserted his faith during college but returned to Christ a dozen years later and entered the Catholic Church at Easter 2004. Among a number of other books, he is the author of On the Meaning of Sex, The Line Through the Heart: Natural Law as Fact, Theory, and Sign of Contradiction, Ask Me Anything: Provocative Answers for College Students, Ask Me Anything 2: More Provocative Answers for College Students, How to Stay Christian in College, What We Can't Not Know: A Guide, The Revenge of Conscience: Politics and the Fall of Man, and Written on the Heart: The Case for Natural Law. J. Budziszewski is on the advisory board of the Catholic Education Resource Center.

Copyright © 2012 J. Budziszewski

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