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As soon as the discussion turns to the comparison between the brains of men and those of women, clichés such as “ men are good at math and women are bad at orientation » are going well. These stereotypical views of gender differences in “nature” suggest that our abilities and personalities are genetically programmed into the brain and unchangeable. However, this is far from being the case, as highlighted in particular by all the knowledge acquired in recent years on the notion of “cerebral plasticity”.
But prejudices remain tenacious, widely relayed in the media but also by certain scientific circles which contribute to promoting the idea of an innate biological determinism of differences in abilities and social roles between the sexes. There have been many publications addressing brain differences between the sexes, but many have long been plagued by bias, misinterpretations, and/or lax methodologies.
So, how can we respond to all these preconceived ideas based on rigorous scientific data? And how can progress in the field of neuroscience help combat the idea of biological determinism of differences in cognitive and behavioral abilities between women and men? It is not a question of denying the differences between the sexes but of understanding their origins. Current scientific knowledge shows that the argument of “natural” differences used to explain differences in abilities, roles or behaviors between women and men no longer holds.
Physiological functions and cognitive functions
The question “does the brain have a sex?” » is at the heart of much research, and has been for decades. Knowing that the brain controls the physiological functions associated with sexual reproduction, we can partly answer in the affirmative. However, the answer is quite different when we look at cognitive functions. Indeed, advances in research on brain development and brain plasticity show that girls and boys have the same brain abilities regarding cognitive functions such as intelligence, memory, attention and reasoning.
Often, the question of brain size has been at the heart of debates. It’s a fact, men’s brains are on average 10% larger than women’s, or around 1,350 kg in men compared to 1,200 kg in women. If we reduce this figure to the average height of individuals (1.78 m for men compared to 1.68 m for French women), this difference remains significant, of around 6%. Furthermore, concerning the internal structure of the brain, several MRI studies have shown variations depending on sex in the volumes of gray matter (where the cell bodies of neurons are concentrated) and white matter (made up of nerve fibers coming from the cell bodies of neurons). Girls have on average a little more gray matter and boys a little more white matter.
There is no difference in cognitive skills
These various observations about brain size and structure have fueled theories purporting to explain differences in behavior, personality or reasoning between the sexes, but all this has been undermined by recent work. First, the structural differences disappear when we take into account the size of the brains as such: in other words, when we compare the brains of men and women of the same volume, we no longer see differences in the proportions of gray and white matter.
“Neither brain size nor the proportions of gray and white matter have an impact on the intellectual abilities of individuals”
Furthermore, it should be noted that neither brain size nor the proportions of gray and white matter have an impact on the intellectual abilities of individuals. Albert Einstein for example with a brain that weighed 1,250 kilos. In fact, the main thing to remember is that no brain is like another. All human beings have different brains regardless of gender.
It is also the knowledge accumulated around the notion of cerebral plasticity which has really made it possible to understand that each brain is different and that variations are not a question of sex. In other words, there are as many differences between the brains of two people of the same sex as between the brains of two people of different sexes.
The brain, a dynamic, “plastic” and adaptive organ
After birth, the construction of the brain is far from complete, because the connections between neurons – synapses – are just beginning to form. The majority of the billions of neural circuits in the human brain are formed from the moment the baby begins to interact with the outside world.
This multitude of connections will be shaped and will evolve in children and adults, in different ways from one individual to another depending on environmental factors, notably our history, our experiences and society. Our brains are therefore plastic, we speak of “cerebral plasticity”. To illustrate this concept, we can take the example of people learning to juggle three balls. After three months of practice, a study based on MRI scans showed a thickening of areas of the brain specialized in vision and coordination of arm and hand movements. When training stops, these brain regions shrink.
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Stereotype threat
As the following experiment shows, gender stereotypes and the simple way a problem is presented can influence an individual’s performance regardless of their knowledge. In this experiment dating from 2014, two groups of middle school students are subjected to the same test which consists of memorizing a drawing then reproducing it. But while in the first group, we describe the test as a “plastic arts” test, in the second group, we speak of a “mathematics” and “geometric figure” test.
Result: the boys obtain better results than the girls in the group taking the test described as “mathematics”, but the girls outperform the boys in the group taking the test described as “plastic arts” (even though these tests are strictly identical). Here, the stereotype according to which girls are less gifted than boys in mathematics unconsciously influences the results.
Theories which claim that, from birth, the brains of girls and boys are distinct – and that these differences explain their roles in society – are based on a fixed conception of brain functioning. They are in total contradiction with the reality of new knowledge on brain plasticity. Continuing to conduct rigorous and ethical studies with interdisciplinary approaches combining biology, neuroscience and human sciences is more necessary than ever to combat stereotypes and essentialist prejudices and understand why human beings are all similar but also all different.
And testosterone in all this?
Testosterone is wrongly called a male hormone: it is present in both sexes, but at different levels. Its concentration in the blood is two to three times higher in men than in women. This is not an absolute rule because testosterone levels vary depending on age and lifestyle. For a long time, it was thought that the action of testosterone on the brain of the male fetus was responsible for typically “masculine” personality traits. The notion of cerebral plasticity once again deconstructs this idea.
Text written in collaboration with Catherine Vidal, neurobiologist and member of the Inserm ethics committee, co-founder of the international research network on the brain and gender (Neurogenderings Network)
