There seems to be an insatiable public appetite for information about sex differences in the human brain, eagerly harnessed by the media in many forms. A paper out this week from a research group at Stanford University made headlines for its innovative contribution to this form: using an AI neural network model to look at brain scans to see if it could “reliably” and “robustly” tell female and male brains apart. In other – more neutral – words, could the algorithm tell whether the brain patterns being looked at were from women or men?
The answer was “yes”, though rather more guarded in the paper itself than in the reports about it. What was interesting about the study was that it seemed to have moved beyond the stereotypical “size matters” agenda – asking whether male or female brains are bigger or smaller in different areas – instead measuring differences in the working brain using a method that looked at differences in blood flow to various brain regions.
Frustratingly, though, when they did find differences, the explanations were just in terms of sex (in the traditional binary, biological sense of the word). We really should stop talking about “male” and “female” brains – and rigidly using that particular lens to evaluate and report on data that is interesting in so many other ways. Arguments about sex differences in the brain have been raging for centuries. Early combatants were pretty outspoken about what they were trying to prove, in particular the inferiority of the female brain. It would be so good to move along from this.
This paper is obviously not wanting to draw any inferences about the value, or even the meaning, of the differences they found, but the impression we are left with – magnified by the media interest it sparked – is clearly reflecting an ongoing “hunt the sex differences” agenda. There seems to be an implacable need, even in today’s world, to find a nice set of biologically programmed, sex-specific differences in the brain, and agree that these must be the basis of any female-male differences in behaviour, or temperament, or ability and achievement.
As for the science itself, there were two key truths that this paper and its coverage overlooked. The first concerns the difference between sex and gender – what, in the olden days, might have been cast as the nature v nurture argument. We now know our brains are malleable and changeable throughout our lives. When you can tell by looking at the scan of an expert musician if they are a keyboard player (spot the symmetrical representation of finger control centres in the brain) or if they play a stringed instrument (cue asymmetrical control centres), this gives a pretty good indication that our brains reflect the lives they have lived or the skills they have acquired. This means that when most studies look at adult scans, they are seeing a brain that has been shaped by lifelong experiences, not just by any potential “hard coded” differences.
The second thing to note about brains is that they have evolved to make us social beings. What nobody, including the authors of the paper, seem to have picked up on is that the areas of the brain that were found to distinguish females and males most reliably are key parts of the social brain network, which has evolved to be uniquely attuned to social interactions, and to pay attention to the outside world and to other people. The default mode network is the part of the brain in which we store key elements of social knowledge acquired by interaction, from the moment of birth (if not before) with the outside world – about yourself and about other people, about social rules and social norms, and even social stereotypes.
The 1,500 young adults in this study were aged between 20 and 35 – just imagine what a treasure trove of experiences will be reflected in their brains. This is not to say that what determines how our brains work is “all culture and no biology”. It is perfectly plausible that there may be sex-related differences in how brains are shaped by social experiences. But it does mean that, when studying diverse groups of human beings, just knowing that the brains come from young female adults as opposed to young male adults will never give us the full picture of where any differences came from.
Researchers should acknowledge that, despite the thousands of research papers with the term “sex differences” in their title, there is little or no consistent and conclusive evidence that any brain differences found can be solely attributed to biological sex.
Essentialist assumptions like these have negative consequences. Only last month, David C Geary, a well-known evolutionary psychologist, said that we should question the wisdom of policy interventions to reduce gender gaps if there was any evidence that they arose from “substantive biological contributions”. Comments on the so-called gender equality paradox cite unspecified “endogenous factors” as an explanation for the fact that that the most gender-equal countries have the greatest underrepresentation of women in science, failing to note that these very countries also have the most entrenched gendered stereotypes about women’s scientific abilities.
If we continue to buy in to the argument that differences between men and women are hardwired, permanent and intractable, then any attempts to address inequalities will all too easily be dismissed, with “what science says” taking the blame.
Prof Gina Rippon is emeritus professor of cognitive neuroimaging at the Aston Brain Centre, Aston University, and the author of The Gendered Brain
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