This morning, all the newspapers are talking about ‘male brains’ and ‘female brains’. A study, published in the top-tier journal PNAS, analyses structural differences between the brains of young males and females aged eight to 22 years.
Their findings apparently support age-old stereotypes of female brains ‘designed for’ social skills, memory, intuitive thinking, and male brains ‘designed for’ co-ordinated tasks, perception. Indeed the senior author, Ragini Verma, is quoted in The Guardian as saying: “I was surprised that it matched a lot of the stereotypes that we think we have in our heads. If I wanted to go to a chef or a hairstylist, they are mainly men.”
The Independent’s front page looks like this:
and they headline an article: “The hardwired difference between male and female brains could explain why men are ‘better at map reading’”
The Huffington Post quite wildly claims: “A new study has confirmed that men and women’s brains are wired in completely different ways, as if they were species from different planets.”
The researchers used a technique called diffusion tensor imaging, which I’m far from qualified to comment on. Using this, they mapped the connections between neurons in the brains of 949 ‘youths’ (428 male).
My problems are two-fold and both relate to the sample analysed in this study.
First, the reporting of the analyses: they don’t mention the magnitude of any differences they found – that is, they do not report effect sizes. Several times, they refer to their sample of 949 as ‘large’ or ‘very large’. Certainly, the sample is over twice that of a previous study (439 people). One thing larger samples let you do is look for smaller effect sizes that are still statistically significant. But we just don’t know what the effects were.
Second, who formed their sample. They studied people aged 8 to 22 years, all recruited from either the University of Pennsylvania or the Children’s Hospital of Philadelphia. They have a fair spread of ethnic diversity within their sample – 44 percent are “Caucasian, not Hispanic” and 40.5 percent are “African American, not Hispanic”, for example. However, the people in their sample may well have grown up in not-dissimilar ways, received similar amounts or quality of education and so on. (We don’t know this, since they only account for individual age and [their words] ‘race’.)
Without looking at variation in upbringing (and the ilk), we can’t discount social or cultural effects – perhaps children growing up in an American culture that says “men should be like this” and “women should be like that” will push them down particular paths, affecting how their brain structures develop. I don’t know, but neither do the researchers.
We cannot talk about ‘hardwired’ differences between female and male brains without understanding the genetic factors, the environmental factors and the interactions and feedbacks between them.
Also, their sample is what has been referred to as WEIRD. That is, Western, Educated, Industrialised, Rich and Democratic. You cannot generalise to all humans from this sample, as the newspapers and as the researchers themselves have been doing.
I’m not saying the researchers ‘should’ have studied a wider, cross-cultural sample who have grown up in and been exposed to different environments – but it’s something to consider before we start saying “women are X” and “men are Y” or, worse, “women should be X” and “men should be Y”.
Madhura Ingalhalikar, Alex Smith, Drew Parker, Theodore D. Satterthwaite, Mark A. Elliott, Kosha Ruparel, Hakon Hakonarson, Raquel E. Gur, Ruben C. Gur, & Ragini Verma (2013). Sex differences in the structural connectome of the human brain PNAS DOI: 10.1073/pnas.1316909110