Study scanned 428 males and 521 females using DTI. Male brains show more front-back connections within each hemisphere. Female brains show more left-right hemisphere connections. Differences exist in children under 13 and grow larger in teens 14-17. Men's wiring explains superior spatial skills and faster action learning. Women's wiring explains better memory for words and faces, intuition, and multitasking. Women excel in social adaptation and concentration. Cerebellum in men has more cross-hemisphere links – in women, within-hemisphere. Brain architecture causes innate complementary strengths between sexes. Gender denial ignores biological brain differences. Early childhood differences rule out pure nurture causation. Pubertal changes amplify sex-specific wiring. Stereotypes of sex differences are neurologically real.