Dump the "dimorphism": Comprehensive synthesis of human brain studies reveals few male-female differences beyond size.
Level 5 - mechanism / opinion, no new human data
Narrative review and synthesis of existing literature without formal systematic review methodology specified in abstract
PubMed 33621637 · doi:10.1016/j.neubiorev.2021.02.026
What was done
The authors synthesized three decades of human postmortem and MRI literature, emphasizing meta-analyses and large-scale neuroimaging datasets to evaluate structural morphology, lateralization, connectomics, and task-based functional MRI across verbal, spatial, and emotion processing.
What was found
Male brains are larger than female brains from birth, stabilizing at an average difference of approximately 11% in adults. This size difference accounts for higher white/gray matter ratios, intra- versus interhemispheric connectivity patterns, and regional cortical and subcortical volumes in males. When structural and lateralization differences are evaluated independent of size, sex/gender explains only about 1% of total variance. Connectome-based sex prediction relies heavily on brain size and performs poorly across diverse populations, while task-based fMRI has yielded no reproducible activation differences.
Why it matters
This review challenges the concept that human brains are sexually dimorphic, showing that structural and functional differences between men and women are largely driven by overall head size rather than distinct male and female brain phenotypes.
Limits
The abstract does not report the total number of studies or individuals reviewed, nor does it specify systematic search, screening, or risk-of-bias protocols. Details regarding demographic representation and how sex versus gender was operationalized are omitted from the abstract.
Cited by
- contradicts Women tend to have a larger hippocampus up until a certain age, while men tend to have a larger cerebellum.