The claim that sex differences are merely socialized has been losing ground in the scientific community for decades as research in genetics, endocrinology, neuroscience, and evolutionary biology has revealed pervasive biological differences between males and females.

Physically, the differences are substantial and well-documented. Males have 30-40% more muscle mass, 10-15% greater bone density, 15-20% higher hemoglobin concentrations, larger hearts relative to body size, greater lung capacity, and different fat distribution patterns. These differences appear after puberty and are driven by hormones, particularly testosterone, which males produce at 10-20 times the rate of females.

Neurologically, male and female brains differ in measurable ways. A 2021 study in Cerebral Cortex analyzing over 30,000 brain scans confirmed consistent structural differences between male and female brains. Males tend to have larger total brain volume and more white matter; females tend to have more gray matter in certain regions. These differences correlate with well-documented differences in cognitive profiles — not superiority, but different strengths.

Psychological research consistently finds sex differences in interests, risk tolerance, empathy, aggression, and occupational preferences. These differences appear across all cultures — including the most egalitarian. Paradoxically, the largest sex differences in occupational choice appear in Scandinavian countries with the most gender equality, a phenomenon known as the 'gender equality paradox.' This suggests biology, not socialization, drives many of these differences.

Simon Baron-Cohen at Cambridge has documented that newborn infants — before any socialization — show sex-typical preferences: boys look longer at mechanical mobiles while girls look longer at faces. These differences exist on day one of life.

None of this means one sex is superior. It means that a one-size-fits-all approach to medicine, education, sports, and policy that ignores biological differences will fail. Good policy requires honest science, and honest science confirms that sex differences are real, measurable, and consequential.