Scientists and anatomists tackle a question that keeps resurfacing in psychology: are behavioral differences between men and women hardwired into the brain or produced by upbringing and culture? The film draws on brain scans of more than 900 people to show how neural pathways and connectivity patterns differ, on average, between the sexes, then tests what those differences actually mean in practice through spatial rotation tasks and emotional recognition challenges. Researchers trace the roots of the divide to prenatal testosterone exposure, and a toy-preference experiment run on unsocialized monkeys is used to argue that some preferences show up before any social conditioning could explain them. Developmental tests on infants add another data point to the nature side of the ledger. The film keeps circling back to its title question, using each experiment as evidence rather than as a lecture, and lets the size gap in brain volume serve as the opening puzzle rather than the conclusion.