For decades, the question of why autism emerges four times more often in boys than in girls has resisted a satisfying answer. New research into fetal brain tissue now suggests the disparity may be rooted not in which genes each sex carries, but in how those genes are organized into networks before birth — a difference in architecture rather than inventory. The same genetic risk, read through differently wired molecular systems, may land with different force depending on the brain in which it finds itself. This discovery invites medicine to think about autism not as a single condition, but as o