“Dump the ‘Dimorphism’: Comprehensive Synthesis of Human Brain Studies Reveals Few Male-Female Differences beyond Size”, 2021-06 (; backlinks; similar):
Meta-synthesis of 3 decades of human brain sex difference findings.
Few male/female differences survive correction for brain size.
When present, sex accounts for about 1% of variance in structure or laterality.
Male and female brains are monomorphic, not dimorphic, in structure and function.
With the explosion of neuroimaging, differences between male and female brains have been exhaustively analyzed.
Here we synthesize 3 decades of human MRI and postmortem data, emphasizing meta-analyses and other large studies, which collectively reveal few reliable sex/gender differences and a history of unreplicated claims.
Males’ brains are larger than females’ from birth, stabilizing around 11% in adults. This size difference accounts for other reproducible findings: higher white matter/gray matter ratio, intrahemispheric versus interhemispheric connectivity, and regional cortical and subcortical volumes in males. But when structural and lateralization differences are present independent of size, sex/gender explains only about 1% of total variance. Connectome differences and multivariate sex/gender prediction are largely based on brain size, and perform poorly across diverse populations. Task-based fMRI has especially failed to find reproducible activation differences between men and women in verbal, spatial or emotion processing due to high rates of false discovery.
Overall, male/female brain differences appear trivial and population-specific. The human brain is not “sexually dimorphic.”
[Keywords: sex, gender, MRI, meta-analysis, corpus callosum, hippocampus, amygdala, massa intermedia, anterior commissure, lateralization, connectome, default mode network, verbal, spatial, mental rotation, emotion, empathy, precision medicine, multivariate, cortical thickness]