What we (don’t) know about gender differences in the brain

November 2, 2017 - 09:00

COMMENT: A Google engineer was recently laid off for writing that biological differences explain why more men than women work in the tech industry. A neurobiologist and science journalist in Denmark agreed with him – but are they right?

The male and female brain are different in some respects. But it is unclear if – and how – these biological differences are related to cognitive gender differences. (Photo: Shutterstock)

A ruckus erupted when Google software-engineer James Damore contradicted his employer’s diversity policy; so much that he was fired.

In an internal memo, Damore claimed that fewer women than men are system developers or leaders because there are biologically determined differences in preferences between the genders.

Women are (on average) more interested in people or social relations, while men (on average) are more interested in things or systems, wrote Damore in an internal memo.

The post caused a public uproar – in Denmark as well. Most were outraged, but not all. Danish science journalist and neurobiologist Lone Frank argued in the broadsheet Weekendavisen and in a debate on the popular show, Deadline, that Damore was right.

According to her, there is well-founded evidence of biologically determined interest differences between the genders. But this evidence is not taken seriously for ideological reasons, says Frank, citing the Swedish sociologist Charlotta Stern who says that the acknowledgement of differences between men and women is "taboo.”

“Denial of facts due to ideology leads directly to unfreedom, and that is exactly what our time’s fanatical gender debate and almost paranoid identity politics is an expression of,” says Frank.

But is it really so?

Scientific consensus on few gender differences

There are only three generally accepted sex-based differences in the brain, which have been demonstrated in multiple surveys: 

  1. Men’s brain are, on average, larger and contain 10 to 15 per cent more brain cells than women’s.
  2. Brain development occurs slower in boys than girls (but the difference disappears towards the end of puberty).
  3. Some cell nuclei in the hypothalamus are larger in men than women.

None of these biological differences are (as of writing) coupled with cognitive differences; that is, our ability to remember, talk, be attentive, make decisions, etc. The difference in the hypothalamus, however, is rather strongly connected to gender differences in sexual preferences.

Throughout the years, many have claimed to have found gender differences in the brain, e.g., in the corpus callosum (which combines the right and left brain hemisphere), the amygdala (which affects our emotions), and the hippocampus (which is linked to memory).

But meta-analyses of the different claims have proven unable to substantiate these differences (in corpus callosum), or been unable to find them after correcting for differences in brain volume (in the amygdala and hippocampus).

Read More: Traditional gender roles are still prevalent in early kindergartens

Gender and cognition – culture or biology?

Meta-analyses have also been unable to document general gender differences in maths and some language skills (vocabulary, spelling, etc.) across cultures.

Recent studies indicate that the gender gap in work, which has previously been described as a result of biology, is culturally determined. The gender gap is not present in groups or cultures where the division of labour is gender neutral. (Photo: Shutterstock)

One exception seems to be reading, where girls perform better than boys. However, reading is not a ‘natural’ trait, but a cultural product that requires instructions to master.

Other cognitive gender differences also seem to be affected by culture, if they are not outright cultural products. For example, we only see gender differences in episodic memory in some groups/cultures whereas other gender differences have diminished drastically over time (e.g., reaction time to visual stimuli).

Most differences are culturally determined

Another relevant area is gender differences in the ability to visually identify and process certain categories of objects. It has been claimed that women are faster than men at identifying and conceptually processing fruits/vegetables while men are better when it comes to animals/tools.

This was explained by evolutionary mechanisms, since men were hunters (animals and tools) while women were collectors (fruits and vegetables). The idea is that specific differences in brain “specializations” have evolved over time.

Newer studies indicate that these differences are also culturally determined, since they are not present in cultures where the division of labour is gender neutral.

But there are no rules without an exception. Meta-analyses point conclusively towards men being better at solving spatial tasks. Even so, gender can only explain 14 per cent (at best) of the variance seen in spatial performance, while the remaining 86 per cent is unrelated to gender.

Read More: How to measure gender equality?

Gender, personality, preferences, and social behaviour

Meta-analyses have documented small to moderate gender differences between:

  • The ability to repress certain behaviour (women +)
  • Impulsivity (men +)
  • Aggression (men +)
  • Helpfulness (men +)
  • Anxiety (women +)
  • Tenderness (women +)

But there is no proof of gender differences in the ability to lead effectively or in emotionality.

On the other hand, there are major differences in preferences. Women are (on average) more interested in people and social relations while men are (on average) more interested in things and systems.

Damore is right in this regard, but it is not necessarily correct that the difference is biologically determined as he and Frank argue.

Difficult to establish causality in gender studies

It requires controlled experiments to say – with some degree of certainty – whether gender differences are biologically or culturally determined. Only through experimentation do we have control over the relevant variables, which allows us to determine causality.  

This is a challenge when it comes to gender differences, because we cannot manipulate the gender (independent variable) and study how this manipulation affects the behaviour (dependent variable).

An example of the type of spatial task where the largest gender difference in cognition has been documented (mental rotation). The test subject must determine if the figures are identical or mirrored. (Figure: Christian Gerlach)

We can only study how the genders differ in regards to behaviour. That makes it difficult to determine whether the differences are caused by biology or culture. Thus, gender studies are based on non-experimental research, which is poor at establishing causality. 

There have been some attempts, though, at demonstrating a relationship between testosterone levels in embryos and gender differences in preferences and behaviour. One study shows that higher levels of testosterone leads to more “boyish” behaviour (violent) during playtime. Another study could not replicate these findings.

This inconsistency is prevalent within the field, which is also host to a full range of interpretation issues. We still do not – and cannot – know if the testosterone directly affects the brain and cause the change in observed behaviour.

It might just as well be caused by testosterone increasing body volume, which then leads to more ‘violent’ games. Normally, it is not possible to measure the amount of testosterone directly in the blood (in embryos). Rather, this is done by measuring the amniotic fluids. But these measurements do not necessarily correlate.

Read More: What happens to girls and boys in gender-neutral preschools?

Animal studies and hormonal imbalances are also unreliable

Considering this, we can look for other approaches. We could study people with hormonal imbalances. Some studies, but not all, find that female embryos with abnormal amounts of testosterone (congenital adrenal hyperplasia) grow up to have more “boyish” behaviour or preferences.

Here it is important to remember that it is always difficult to establish the ‘normal’ based on the ‘abnormal.’ For that reason it is an indirect conclusion.

Another approach is animal studies. In these studies it is possible to directly manipulate the amount of hormones that the organism is exposed to at any given time – while keeping the environment stable. Here we have more control over the variables, but the problem is that animals aren’t people and that hormonal effects can be species-related.

In other words, animal studies are rarely good at explaining complex human behaviour, such as job preferences.

Gender differences and ideology

As described above, there are gender differences in the brain, but it is unclear if – and how – they are connected with cognitive differences. The same must be said about the relationship between hormones and gender differences in cognition, social behaviour, and preferences.

Compared with this, there is less doubt that gender differences can be cultural products. However, given that it is difficult to establish a causality, there is still room for ideological interpretations. And that is completely without denying the facts. That is probably the only thing that can be concluded with certainty in this debate.

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Read this article in Danish on ForskerZonen, part of Videnskab.dk
 

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Translated by
Kristian Secher

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