The findings, published in the Neuroscience and Biobehavioral Reviews, indicate that size is the only clear-cut difference between male and female brains.

Women's brains are about 11 per cent smaller than men's, in proportion to their body size. Smaller brains allow certain features, such as a slightly higher ratio of gray matter to white matter, and a higher ratio of connections between, versus within, cerebral hemispheres.

"This means that the brain differences between large- and small-headed men are as great as the brain differences between the average man and woman", said researcher Lise Eliot from Rosalind Franklin University in the US. "And importantly, none of these size-related differences can account for familiar behavioural differences between men and women, such as empathy or spatial skills", Eliot added.

For the study, the team conducted a meta-synthesis of three decades of research, assimilating hundreds of the largest and most highly-cited brain imaging studies addressing 13 distinct measures of alleged sex difference. For nearly every measure, they found almost no differences that were widely reproduced across studies, even those involving thousands of participants. For example, the volume or thickness of specific regions in the cerebral cortex is often reported to differ between men and women. However, the meta-synthesis shows that the regions identified differ enormously between studies.