Jun 26 2018

Male and Female Brains Revisited

There is a seemingly endless debate about whether or not, and how, male and female brains differ. This is also an extension of the also endless nature vs nurture debate.

Unfortunately these questions get tied up with social, political, and ideological questions. I say unfortunately because they really shouldn’t be. Ideally we can ethically recognize that the optimal position is to respect every human’s rights and dignity. Everyone should be afforded the same basic rights and opportunity to pursue their potential and desires.

This ethical position can be valid even if it turns out to be true that not every human being is identical in terms of their potential or inclinations, or whether or not there are identifiable subgroups of people. These are scientific questions that should be approached and answered scientifically.

Historically, the science has been abused, suppressed, or altered for ideological purposes. It then becomes tempting to push back with science on the other side, but this, in my opinion, is misguided. Better to simply divorce the scientific questions from the ethical questions. Even in a world where there are statistical differences between identifiable groups we can still agree that every person deserves equal rights and dignity. That way an important ethical position does not become dependent upon a certain scientific finding.

Male and Female Brains

A frequent question of debate is whether or not there are “hardwired” differences, on average, in male and female brains. Even if the answer seems obvious, it isn’t, because whatever differences you perceive can be entirely environmental and learned. Culture is powerful, and can plausibly determine any observed sexual differences.

Also, I put “hardwired” in quotes because this really is a flawed metaphor. The brain is not hardwired – it is wetware, “softwired” at best. This is because the “wires” in the brain are living cells, that can change and adapt.

The brain is also an organ specifically evolved to interact with and adapt rapidly to the environment. The brain learns and has memory, it has plasticity, and is always changing. Further, in the brain’s “wetware” the hardware and software are essentially the same thing.

So just from our basic understanding of the brain, and certainly supported by decades of research, we should expect a complex relationship among genetic predisposition, developmental factors, and everything in the environment in terms of brain function. Genes do not completely determine outcome, even if they have an influence.

In a recent Atlantic article, Lise Eliot, a professor of neuroscience at the Chicago Medical School, says:

“People say men are from Mars and women are from Venus, but the brain is a unisex organ. We have the exact same structures. There is absolutely no difference between male and female brains.”

I think this is overstating the situation. She further says:

“The average male is more aggressive than two-thirds of females,” she said, “but that also means one-third of females are more aggressive than the average male.”

That does not support her position, however. A difference does not have to be absolute to be real. In any case, we are usually talking about statistical differences between group averages, not every single individual.

We can break this down to several subquestions – are there measurable differences between males and females in terms of group statistics, to what extent are any differences due to nature vs nurture, and what is the relative magnitude of any differences when compared to individual variation?

The answer to the first question is clearly yes. The curves for males and females (taking a binary approach, which itself is an approximation, but that’s a different discussion) for many traits are distinct, even if they overlap considerably.

The nature vs nurture question is extremely complex, but I think the bottom line answer is that both are in play. This varies from trait to trait, and from person to person. Extreme environmental factors may overwhelm genetic predisposition, and extreme genetic phenotypes may overwhelm environmental factors, for example. But for most traits for most people there is a complex interplay between genetic potential and environment.

The last question is perhaps most interesting – what is the magnitude of any differences compared to individual variation. I think this is where most people like Eliot wash over some of the complexity and characterize the situation as – no difference. But that is not strictly true.

I discussed this issue in 2015 when reviewing the results of an extensive fMRI study comparing male and female brains. We can talk about two kinds of difference – categorical and statistical. A categorical difference is when a trait exists entirely in one group and not the other, with no overlap. A statistical difference is when the groups overlap in any given trait, but the curves are statistically shifted.

What the extensive study found is that there are no categorical differences between male and female brains, but there are statistical differences. This is why some people can say there are no differences and other people say there are differences – they are referring to different things, categorical vs statistical.

Further, the review found that there is no real consistent pattern to the statistical differences. This means that each individual person is a mosaic of different neurological traits, there is no real male or female pattern. Further, the differences within each sex are greater than the statistical differences between the sexes.

One way to look at this pattern is this – by knowing someone’s sex alone, you cannot predict their neurological traits. By comparison, we can say that men are statistically taller than women, but knowing someone’s sex does not allow you to know their height.

So how do we summarize all this? I think it is a profound mistake of science communication to summarize this by saying, “There is absolutely no difference between male and female brains.” This statement is too absolute, and easily refuted, calling into question the deeper reality which is more important.

The real summary is more nuanced – there are no categorical differences between male and female brains. There are statistical differences, but these are small and less than individual variation.

We need to further point out that genetics and development are not destiny – they appear to create, at most, a predisposition, which then interacts with the environment, which also has a powerful effect.

If we want to go one level deeper we can point out that knowing one’s sex does not tell you anything significant about their math ability, their aggressiveness, or their empathy, any more than it tells you about their height.

All of this, by the way, applies to the concept of race. Knowing someone’s continent of origin of their ancestors only gives you statistical information about some traits, but cannot be used to predict anything important about the individual. There are statistical differences only, with large overlap (meaning greater individual variation), and no categorical differences.

This does not mean that races do not exist, as some claim, in my opinion. It only means that we need to put the concept of race into its proper context – it may exist statistically, but really doesn’t tell us much about an individual. It has some use in medicine, where statistics are used as a basis of decision-making.

And to emphasize my original point – none of this should determine our ethical positions. Even if it turned out to be the case that there were categorical difference between sexes or among races, that would not justify racism or sexism. We could (and, I would argue, should) collectively decide that it is important to respect people’s humanity above any differences they may have.

But it also happens to be the case that sexual and racial differences are all statistical and minor compared to individual differences, and the influence of the environment. Education, opportunity, and fairness all have an overwhelmingly large impact on any trait we care to measure, when compared to these minor statistical differences.

I think that is an important bottom line message to convey, and I worry it gets lost when oversimplified to the easily refuted version of – there is no difference.

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