The Brain Binary

How Real Are Male & Female?

Are male brains really that different from female brains? Does it matter? Why should anybody care?

In 1873, Dr. Edward Clarke, a professor of medicine at Harvard Medical School, published a book titled Sex in Education: or, A Fair Chance for the Girls. Dr. Clarke proclaimed that if a girl spent too much time studying or playing competitive sports, she would divert blood away from her uterus, rendering the unfortunate girl “irritable and infertile.” When Dr. Clarke wrote that he wanted girls to have “a fair chance,” he meant a fair chance to become a mother and a housewife. Dr. Clarke’s book became a bestseller and inspired state legislatures to enact official bans on girls in competitive sports, some of which remained in place for decades. More than 50 years later, in 1925, the National Association of Secondary School Principals voted 72 to 7 to ban extramural sports for girls.

Twenty-seven years after Dr. Clarke published his bestseller, German neurologist Paul Julius Möbius published a scholarly monograph titled Über den physiologischen Schwachsinn des Weibes, “Regarding the physiological weak-mindedness of women.” Möbius noted that women have brains which are significantly smaller than the brains of men, even after adjusting for differences in height. He concluded that women are “physiologically weak-minded.” In making that claim, Möbius was continuing a tradition in Western thought which we can trace back to Aristotle, namely, that women and men are different—and that men are better.

 “The Idea of Gender” 

Twentieth-century feminism was an attempt to push back against Dr. Clarke, Dr. Möbius, Aristotle, and all the other misogynists who insisted that there are hardwired differences between men and women and that those differences mean that men are better and women are disqualified. Second-wave feminists of the 20th century, such as Gloria Steinem, Betty Friedan, and Shulamith Firestone, sought to deconstruct the systemic and legal barriers which blocked women from equality. But those women did not challenge the gender binary, the division of the human race into male and female.

That changed with Judith Butler. Butler, a professor of comparative literature at the University of California, Berkeley, took a sledgehammer to the gender binary. In 1990, Butler wrote in her book Gender Trouble that “because gender is not a fact, the various acts of gender create the idea of gender, and without those acts, there would be no gender at all.” For this insight, she was rewarded with an avalanche of scholarly honors and prizes, including the Mellon Prize, which earned Professor Butler a $1.5 million cash award. (By comparison, the Nobel Prize gets you less than $1.1 million.)

Butler’s claim that gender is a social construct, not a biological fact, has become widely accepted at leading universities worldwide in the decades since the publication of Gender Trouble. A few years back, Cordelia Fine, professor of history and philosophy at the University of Melbourne, published a book titled Testosterone Rex: Unmaking the Myths of Our Gendered Minds (2017). Following Butler, Fine asserted that any claims that women and men differ significantly in brain or behavior are simply lies perpetuated by the heteronormative patriarchy. Fine’s book promptly received the Royal Society’s prestigious prize for best science book of the year.

Demonstrated  Differences

The worldview promulgated by Butler, Fine, and their followers now constrains what neuroscientists are allowed to say. A professor of neurophysiology at Lund University in Sweden told undergraduates that the categories of female and male are, to some degree, biological realities rather than social constructs and that some differences in behavior between women and men might, therefore—maybe, just maybe—have a biological basis. He was promptly denounced by students who claimed that his remarks were “anti-feminist.” The dean of the medical school duly launched an investigation.¹

The arguments of men from Aristotle to Möbius have made many modern researchers understandably leery of arguments regarding female/male differences in the brain. And researchers have long since established that there are, in fact, no differences in average intelligence between men and women. But investigators have consistently found that women are more likely than men to suffer from anxiety and depression.² Conversely, men are more likely than women to be diagnosed with autism,³ attention-deficit disorder,⁴ and schizophrenia.⁵ Are these male/female differences merely social constructs? Or might these robust differences in psychopathology reflect at least in part some underlying differences in neuroanatomy or neural connectivity?

A recent review of MRI studies of female and male brains concluded that “MRI-based studies exploring differences between male and female brains revealed mostly inconsistent and inconclusive findings.”⁶ Others have argued that while there might be differences, on average, between male and female brains, the differences lie on a continuum with lots of overlap.⁷

But researchers at Stanford Medical School recently used deep learning artificial intelligence methods to examine brain activity in roughly 1,500 young adults 20–35 years of age.⁸ Neuroscientists have known for many years that every human brain is characterized by a “fingerprint” of brain activity at rest, unique to that individual.⁹ The Stanford neuroscientists used artificial intelligence techniques to determine the fingerprint of every one of those young adults and then compared females with males. Did females differ from males? Was there overlap?

The results were astonishing:

As you can see, there wasn’t a continuum: the female fingerprints of brain activity were quite different from the male fingerprints of brain activity, with no overlap. These findings strongly suggest that what’s going on in a woman’s brain at rest is significantly different from what’s going on in a man’s brain at rest. And the variation among the women, as well as among the men, was smaller than the difference between the sexes.

Just as remarkably, the Stanford team used artificial intelligence methods to map fMRI (functional MRI) patterns of connectivity onto cognitive functions such as intelligence. They found particular patterns of anatomy and connectivity within male brains which accurately predicted cognitive functions such as intelligence among the men. But that male model had no predictive power for cognitive functions in women, as shown below.

Conversely, they found patterns of anatomy and connectivity within female brains which accurately predicted cognitive functions such as intelligence among women. But that female model had no predictive power for cognitive functions in men, as shown:

These findings strongly suggest that whatever determines intelligence in the brains of men is completely different from the determinants of intelligence in women. And whatever determines intelligence in women is completely different from the determinants of intelligence in men.

The researchers are well aware of the implications of their findings. They know all about the previous studies suggesting small effect sizes, lots of overlap, and a continuum of male/female difference. They conclude that the failure of previous work to demonstrate the effects they found is due to the “weaker algorithms” employed in earlier research. They conclude: “Our results provide the most compelling and generalizable evidence to date, refuting this continuum hypothesis and firmly demonstrating sex differences in the functional organization of the human brain.”

There has been very little coverage of this report in the mainstream media. You will find no mention of it in The New York Times, The Wall Street Journal, or National Public Radio. But the study has not gone unnoticed. Followers of Judith Butler are aware of the study and have responded. Gina Rippon, a Butler disciple, noted that all the study participants were ages 20–35 years old.¹⁰ “Just knowing that the brains come from young female adults as opposed to young male adults will never give us the full picture of where any differences came from,” she objected. “It is perfectly plausible that there may be sex-related differences in how brains are shaped by social experiences,” she countered—perhaps something like 20–35 years’ exposure to heteronormative Western patriarchy (all subjects were from the United States or Western Europe). Are the differences hardwired, or socially constructed? Nature or nurture? If gender is just a performance, then 20 years of performing may have changed the brains to produce the differences found by the Stanford researchers. Maybe.

Differences  in Utero

But Rippon herself shows no awareness of other studies showing that these sex differences are actually present prior to birth. For example, a team of American researchers used high-resolution MRI scanners to examine the brains of babies still in their mothers’ wombs, in the third trimester of pregnancy.¹¹ They found dramatic differences in the connections within the brains of boys compared with those of girls, anticipating the differences found in the Stanford study.

Likewise, researchers at the National Institutes of Health have tracked a large cohort of children, with each child coming in year after year to have his or her brain scanned.¹² Girls’ brains are smaller than boys’ brains, at every age, and girls mature faster than boys do. Girls reach the inflection point—indicated by the arrow, roughly the halfway point in brain development—around 11 years of age (see graph below). Boys don’t reach the inflection point until around 15 years of age. Girls reach full maturity in brain development by roughly 22 years of age. Boys don’t reach full maturity until about 30 years of age.

 Vive La Différence

As it turns out, that old German neurologist Dr. Möbius was not wrong on the data. Women do have smaller brains than men. But when he concluded that women were therefore weak-minded, he was assuming that women’s brains and men’s brains operate in the same way. They do not. When a woman and a man are both doing the same math problem, for example, they are using very different brain regions: men’s brains are more compartmentalized; women use more areas of the brain for the same task.¹³ Women’s brains are smaller but develop faster and function more globally. Men’s brains are somewhat larger but apparently are more pigeon-holed.

Differences do not imply an order of rank. Apples and oranges are different. That doesn’t mean apples are better than oranges. Ovaries and testicles are different. That doesn’t mean ovaries are better than testicles, or vice versa.

The gender binary is not an arbitrary social construct. It is a biological reality, manifest in the organization of the human brain prior to birth. Men and women are different. That doesn’t mean men are better or that women are better. It does mean, or should mean, that we need to work harder to understand the differences. A better understanding of the differences might improve our ability to prevent and treat those conditions that are gender-weighted, such as autism and psychotic disorders among men, and anxiety and depression among women.

Genesis 1:27 reads, “In the image of God he created him; male and female he created them.”It doesn’t say “Black and white he created him.” It doesn’t say “Asian and Hispanic he created him.” Black, white, Asian, and Hispanic are, for the most part, man-made. But male and female are of God. 

Notes
1. “Swedish Professor Accused of Bigotry for Saying Men and Women ‘Biologically Different,’” RT (Sep. 17, 2018).
2. Gobinath et al., “Sex, Hormones, and Genotype Interact to Influence Psychiatric Disease, Treatment, and Behavioral Research,” Journal of Neuroscience Research, vol. 95 (2017), 50–64.
3. Donna Werling and Daniel Geschwind, “Sex Differences in Autism Spectrum Disorders,” Current Opinion in Neurology, vol. 26 (2013), 146–153.
4. Arnett et al., “Sex Differences in ADHD Symptom Severity,” Journal of Child Psychology and Psychiatry, vol. 56 (2015), 632–639.
5. Gur et al., “Schizophrenia Throughout Life: Sex Differences in Severity and Profile of Symptoms,” Schizophrenia Research, vol. 21 (1996), 1–12.
6. Eileen Luders and Florian Kurth, “Structural Differences Between Male and Female Brains,” Handbook of Clinical Neurology, vol. 175 (2020), 3–11.
7. Zhang et al., “The Human Brain Is Best Described as Being on a Female/Male Continuum: Evidence from a Neuroimaging Connectivity Study,” Cerebral Cortex, vol. 31 (2021), 3021–3033.
8. Ryali et al., “Deep Learning Models Reveal Replicable, Generalizable, and Behaviorally Relevant Sex Differences in Human Functional Brain Organization,” PNAS, vol. 121 (2024).
9. Emily Finn et al., “Functional Connectome Fingerprinting: Identifying Individuals Using Patterns of Brain Connectivity,” Nature Neuroscience, vol. 18 (2015), 1664–1671.
10. Gina Rippon, “Take It from a Neuroscientist: Searching for a ‘Male’ and ‘Female’ Brain is a Waste of Time,” The Guardian (Feb. 22, 2024).
11. Wheelock et al., “Sex Differences in Functional Connectivity During Fetal Brain Development,” Developmental Cognitive Neuroscience, vol. 36 (2019).
12. Giedd et al., “Review: Magnetic Resonance Imaging of Male/Female Differences in Human Adolescent Brain Anatomy,” Biology of Sex Differences, vol. 3 (2012).
13. Katherine Keller and Vinod Menon, “Gender Differences in the Functional and Structural Neuroanatomy of Mathematical Cognition,” Neuroimage, vol.   47 (2009), 342–352.