Gina Rippon writes: The latest neuroscientific techniques employed to measure and map those brain structures and functions which might distinguish the two sexes are discussed in a recent special issue from the Royal Society. Daphna Joel had previously published a study of structures and connections in over 1,400 brains from men and women aged between 13 and 85, in which no evidence was found of two distinct groups of brains that could be described as either typically male or typically female. Brains were more typically unique “mosaics” of different features – something more correctly characterised as a single heterogeneous population.
Such a mosaic of features cannot be explained in purely biological terms; it is a measure of the effect of external factors. This is true even at the most fundamental level. For example, it can be shown that a “characteristically male” density of dendritic spines or branches of a nerve cell can be changed to the “female” form simply by the application of a mild external stress. Biological sex alone cannot explain brain differences; to do so requires an understanding of how, when and to what extent external events affect the structure of the brain.
The notion that our brains are plastic or malleable and, crucially, remain so throughout our lives is one of the key breakthroughs of the last 40 years in our understanding of the brain. Different short- and long-term experiences will change the brain’s structure. It has also been shown that social attitudes and expectations such as stereotypes can change how your brain processes information. Supposedly brain-based differences in behavioural characteristics and cognitive skills change across time, place and culture due to the different external factors experienced, such as access to education, financial independence, even diet.
The importance of this to the male/female brain debate is that, when comparing brains, it’s necessary to know more than just the sex of their owners.
Understanding how much the brains being examined are entangled with the worlds in which they exist must be part of any attempt to try and answer the question of what, if anything, separates male and female brains.
What is really meant by a “sex difference”? Taken straightforwardly, one would assume a “difference” implies the two groups measured are distinct. That the characteristics true of one are almost always not true of the other, that it’s possible to predict characteristics based on sex or vice versa, or that knowing to which group an individual belonged would allow you to reliably predict their performance, responses, abilities and potential. But we now know that this simply doesn’t reflect reality.
On a wide range of psychological measures, it’s clear that the two sexes are actually more similar than different.
The whole issue of male/female differences in the brain and the implications for male/female differences in any sphere – normal or abnormal behaviour, ability, aptitude or achievement – is really important to clarify. In the US, the National Institutes of Health recently mandated that, where appropriate, sex of the test subjects should be a variable in any research it funds.
