Short answer
The male and female brain differ, but they are more alike than they are different. Moreover, the differences between male and female brains are smaller than the differences between male brains within themselves or the differences between female brains within themselves. There are also differences in some skills and preferences between men and women, but these are not constant over time or across countries, which suggests that there are very strong social and cultural factors that explain why men and women differ on average in their behavior.
Longer answer
Disclaimer
Firstly, it is important to start with some disclaimers as the biology behind the entire spectrum of both gender and sex is a complicated topic and is beyond the scope of this answer. We will, however, get into this in the near future! To answer this question, we will therefore only be talking about cis-men (people who were assigned male at birth, and identify as male) and cis-women (people who were assigned female at birth and identify as female).
Secondly, we have to be careful in our interpretation, because throughout history the answer to this question played an important role in the debate of gender equality. For example, brain science results showing that men and women may differ, in any type of way, are taken as the reason for stereotypical gender differences, or even as support for those claiming that women are less intelligent than men. To be clear: This is not the case! Men and women were found to be equally intelligent. To cut a long story short: the male and female brain do differ, but they are more similar than they are different. Moreover, the differences between male and female brains are smaller than the differences between male brains or the differences between female brains.
Thirdly, even if we find a difference between male and female behaviour or skills, it is very difficult to say whether this difference is innate (due to genetics/biology), or due to for instance stereotypes in culture or upbringing. There is for instance a complex interaction between heritable and environmental effects on scores on IQ tests.
Now that these important points are settled, let us look at where there actually may be some differences between the brains of men and women.
Genetic and hormonal differences
We can often see that women and men differ based on their physique, this is due to their genetics and biological development. The genetic data that we receive from our parents determine whether we are (in most cases) born as a boy or a girl, and what types of hormones (most) stimulate our growth. Men will have more of the typical male hormones (for instance testosterone) running through their body, and women will have more of the hormone oestrogen (Check the links below to find out more about these hormones).
These sex hormones play an important role in the development of the brain, during pregnancy and early life. Female fetuses do not produce hormones, but male fetuses start producing testosterone in the womb and this increase in testosterone around birth will ‘masculinize’ the developing brain. These hormone-induced changes result in some differences in the number of brain cells and connections in specific brain areas that will affect the way these brain areas will function. The mother also produces hormones (including testosterone), which also influence the development of the fetus’ brain. This means that in the absence of hormones, the brain will develop into a female brain, and that testosterone levels during pregnancy determine how ‘male’ the brain becomes. When the baby is born, hormone levels remain low for the first ten years of life, but brain development is further determined by sex hormones (testosterone in males and estrogen in females) during puberty. The brain does not reach its adult form until around the age of 20-25. During all these years, sex hormones influence brain development, but you can imagine that this is only one of many influential factors that determine brain development.
In addition to brain development, the level of sex hormones also stimulates male or female physical characteristics, and therefore certain skills. That is why, for instance, the Olympic committee has argued that women with a testosterone level higher than a set maximum, are not allowed to compete with the other women, as it would give them an unfair physical advantage. A typical effect of high levels of testosterone is that it boosts your confidence. As an example, women with chronic anxiety have received short-lasting testosterone treatment, which much improved their symptoms (i.e. made them more confident). Importantly, this does not mean that all women with anxiety should be treated with testosterone because it has considerable side effects that may not be desirable (like stimulated hair-growth, or other behavioural side-effects). Still, it shows the impact of this hormone on self-confidence and anxiety. Interestingly, multiple studies have shown that men with on average higher testosterone levels tend to overestimate their own abilities a little, while women as a group tend to underestimate themselves. So, in the bigger picture, there appear indeed to be hormone-induced differences in behaviour between the sexes.
Differences between the brains of men and women
Male and female brains are very similar. They have the same shape and the same brain regions. They do differ though, as women have smaller brains, and fewer brain cells, even if we take into account that they tend to have smaller bodies. In the first place, as stated before, this does not mean that they are less intelligent! A study looking into how these brain cells communicate with each other found that brain cells in women seem to make more connections with other brain cells than those of men, and that women use the energy sources of their brain cells more efficiently. This may be why women need fewer brain cells, to be equally intelligent.
Why are there so many more men working in technology, science or mathematics?
As an example of the complexity of the interactions between gender differences and their effects on society, we will discuss the question of why men are overrepresented in some professions, such as those oriented towards technology or science,
Differences in skills
As mentioned above, there has been a long debate about whether men and women differ in certain skills. Although no differences in IQ have been found, differences have been found in some skills, such as some verbal skills (where women generally score somewhat better) and some visual-spatial skills (where men generally perform somewhat better). The causes of these differences are unknown, but are most likely a complex mix of cultural, social and biological factors. Moreover, these average differences are usually small compared to the differences within a group (the differences between men and women are much smaller than the differences between women or between men). Therefore, differences in skills cannot explain why more men work in technology, science or mathematics. Moreover, gender differences in occupations show strong differences between countries. In the GDR and the USSR, for example, where everyone had to work regardless of their gender, these differences in preferred occupations were much smaller. This suggests that there are cultural differences that play an important role. Gender equality also appears to have a strong effect on test scores between girls and boys, especially in math and reading comprehension (see the article Culture, Gender, and Math below). Girls underperform boys in math in Turkey, but outperform boys in Iceland.
Differences in preferences or interests
It has often been argued that men and women simply like different things, and that men are more into math or programming than women. There do appear to be differences in interests, but researchers do not find the same differences in interests across countries and these seem to change over time, suggesting that differences in interests between men and women are strongly influenced by culture and society.
Conclusion
Biological differences, gender roles, and cultural upbringing interact with differences in abilities and preferences in complex ways. The effects of culture, society, stereotypes, and expectations are usually very large. There are large individual differences in brain function between people, and these individual differences are much larger than the sex differences.
NB We consulted Iris Sommers, Marlene Meyer and the Donders Diversity Committee in answering this question.
Read more?
Culture, Gender, and Math – article by Luigi Guiso on how gender (in)equality affects test scores
(Dutch) Het VrouwenBrein, Iris Sommer
(Dutch) Dit doet testosteron écht met je gedrag – De Correspondent
Sex Differences in the Brain (brainfacts.org)
Wikipedia page about sex differences and intelligence
The Science of Sex Differences in Science and Mathematics
Testosterone & Oestrogen:
Testosterone — What It Does And Doesn’t Do – Harvard Health
Oestrogen’s Effects on the Female Body | Johns Hopkins Medicine
Hammes, S. R., & Levin, E. R. (2019). Impact of oestrogen in males and androgens in females. The Journal of clinical investigation, 129(5), 1818–1826. https://doi.org/10.1172/JCI125755