How many times have we heard the argument repeated, that women and men are different because our brains are different? Smaller or larger brain areas associated with certain behaviors, the argument commonly goes, puts the sexes at odds on everything from academic preferences to remembering anniversaries.
And this isn’t just a belief that spawns memes around social media, it’s also the topic of popular science books lining rows of shelves. Brain differences across the sexes is big business.
Neuroscience, however, would have us pause and ask harder questions. As is so often the case, the situation changes when we shift from first glance conclusions to less easily categorizable evidence.
Speaking at Neuroscience 2025, the Society for Neuroscience’s annual conference, Dr. Catherine S. Woolley addressed the topic with a presentation titled, “Sex Differences in the Brain are Misunderstood.” As the title suggests, our popular conceptions about male and female brains could stand some rethinking.
Dr. Woolley, a neuroendocrinologist from Northwestern University, sketched a helpful way to think about the topic, starting with a broader, macro view and gradually moving toward a more nuanced micro view.
From the macro view, it may first appear that our brains are significantly different, at least in the sense that on average certain brain areas may be smaller or larger, or more or less dense, in women and men. And if we leave the analysis there, it takes just one more step to erroneously link behavioral differences to those brain differences.
That’s the sort of reasoning that many relied on for decades to support conclusions like the male brain being more natively structured to handle engineering and scientific subjects, which we now know is utter bunk.
As Dr. Woolley explained, human brains are really a “mosaic” – a mixture of likenesses and differences, and on average those differences aren’t terribly significant.
“Population sex differences in the human brain are numerous, go in both directions, and are very small,” she added.
It isn’t until researchers drill down to the molecular level—shifting to the micro view— that more differences are seen, and even then only when using certain chemicals to illicit reactions from brain tissue in experiments.
At this micro level, Dr. Woolley believes brain differences between the sexes are meaningful and neuroscience is uncovering more about them, but at this point we also don’t understand nearly enough to make firm conclusions – certainly not enough to say this or that behavior is linked to sex differences.
“Be very careful about trying to extrapolate behavioral differences from molecular differences,” she cautioned.
But what about hormones? It’s often assumed that one of the key differences in male and female brains is the level of hormonal exposure in the female brain.
Well guess what, the same is true of male brains. “Hormones matter in both females and males, not just females,” said Dr. Woolley. The science on testosterone in particular backs up that position.
When we’re discussing behavioral differences linked to brain sex differences, what we’re really talking about is the “entanglement between sex and gender.” In popular parlance, it’s almost impossible to separate sex and gender. We bake countless assumptions into what we think we know about our brains, and most of those are strongly colored by what we think we know about gender.
Coming back for a moment to an assumption I mentioned earlier, about what people thought they knew about the male and female brains’ ability to tackle challenging science and similar subjects, Dr. Woolley gave this example: neuroscience PhD degrees awarded over time. From 1980 to the early 2000s, the majority of neuroscience PhDs were awarded to men at about a 60/40 ratio. And then around 2005, the percentages started shifting and women began receiving more neuroscience PhDs, and the ratio now significantly favors females.
So what happened? Was there a radical change in brain structure between the sexes that suddenly gave women the edge? Of course not. Other factors in society and culture changed and opened pathways for women to advance in neuroscience and a host of related fields. What we thought we knew about brain differences underlying the sexes’ ability to do hard science was simply wrong.
Which leads to what I think is the most important takeaway from this analysis. When you hear someone confidently linking a behavior to brain sex differences, as if it’s just an obvious fact of nature, remember Dr. Woolley’s work. Whether you choose to correct them or not, keep in mind that we’re nowhere near drawing such conclusions, and whatever we think we know is tightly entangled with cultural assumptions and misunderstandings.
In short, as with so many brain topics, we’d do well to pause, reflect, and ask harder questions. Superficial reasoning rarely tells us the real story.
