We present a systematic meta-synthesis of structural diffusion MRI and functional connectomic datasets encompassing over 2,400 adult participants across four multinational cohorts. Rather than segregation into dimorphic archetypes, individual human brains exhibit heterogeneous mosaics of masculine-leaning, feminine-leaning, and intermediate connectivity modules.
01. Historical Dichotomy vs. High-Resolution Connectomics
For over a century, neuroanatomical inquiries operated under the assumption that sexual reproduction mandates a dichotomous structural template for the human central nervous system.
However, contemporary neuroimaging syntheses pioneered by [Joel et al., 2015] demonstrated that sexual dimorphism in human brains does not assemble into two discrete packages. When analyzing 116 sexually dimorphic structural features in voxel-based morphometry, individuals possessing consistently "male-end" or "female-end" scores across all measures comprised less than 8% of the examined cohort.
The Continuum of Morphological Overlap
"When you control for head size, sex differences in subcortical volumes diminish toward zero. The human brain is not sexually dimorphic; it is sexually polymorphic."— Lise Eliot et al., Neuroscience & Biobehavioral Reviews (2021)