Cited as the largest single-sample study of structural and functional brain sex differences ever undertaken and published in a peer-reviewed journal, it involved some 5000 participants – 2 466 male and 2 750 female.
The study published in Cerebral Cortex demolishes the fashionable notion that gender is a social construct, and that men and women are the same. The team of researchers from Edinburgh University, led by Stuart Ritchie, found that men’s brains are generally larger in volume and surface area, while women’s brains, on average, have thicker cortices.
“The differences were substantial: in some cases, such as total brain volume, more than a standard deviation,” researchers noted. Ritchie is also the author of Intelligence: All That Matters.
Men, on average, have bigger brains than women. And total brain volume and IQ are correlated, a 2015 meta-analysis of 88 studies involving 148 mixed sex samples comparing magnetic resonance images of people’s brains with their cognitive test scores, showed. They found that the association between brain volume and cognitive ability across a range of different IQ domains (full-scale, performance and verbal IQ) applied to differences in men and women.
Another study led by Richard Haier, author of The Neuroscience of Intelligence, also showed that total brain volume accounts for about 16 per cent of the variance in IQ.
Ritchie’s team found that men in their sample scored, on average, scored fractionally higher than the women on a test of verbal-numerical reasoning and recorded slightly faster processing speeds on another test. After extensive statistical analysis, they concluded that the modest sex differences in verbal-numerical reasoning were almost entirely due to differences in brain volumetric and surface area measures.
Ritchie’s latest research complemented a 2008 study of male-female IQ differences – also done by a team from Edinburgh – which found that men outnumbered women at either end of the cognitive bell curve. So greater variability was noted among men when it came to cognitive ability.
This echoed the conclusion of a 2007 paper which found that among those scoring in the top two per cent of the Armed Forces Qualification Test, men outnumbered women by a ratio of 2:1.
This study confirmed that explanations of the gender gap in IQ variability that rely entirely on cultural/social factors were not based on science. Angela Saini argued against the findings, saying that the reason men outnumbered women by 2:1 among the top two per cent was because boys “received more praise and encouragement than girls”.
One study, often quoted, showed that IQ can be raised by the Abecedarian Early Intervention Project. But the number of children in that study was only 111, with just 57 in the treatment group, thus not nearly substantial enough to be conclusive.
It also begs the question of why there is a higher preponderance of men in the left-hand tail of the bell curve. Do boys who struggle with basic arithmetic receive less encouragement than girls?
Only nine per cent of the UK’s engineering workforce is female and male science professors outnumber female science professors by a higher ratio than 2:1.
As Canadian academic Jordan Peterson pointed out to Cathy Newman on Channel 4 News, men outnumber women in professions dealing with things such as computer science, and women outnumber men in fields dealing with people, such as nursing.
Several international studies support Peterson’s argument, showing that the more gender equality there is in a society, the lower the percentage of women going into engineering and tech, implying that women are exercising their free will, as The Atlantic report headlined recently: The More Gender Equality, the Fewer Women in STEM.
Actually, women who score in the top two per cent or higher for general cognitive ability are more likely than men to have strong verbal scores, meaning they have more career options than their male counterparts.
The differences between men and women would also suggest that gender parity in STEM fields is unlikely to be achieved without state intervention.