Are men innately more violent? Are women innately more people-focused? What explains gay people, campness, transgenderism? How much of the sex differences are cultural, and how much is hardwired by our evolutionary psychology?

The science of the sexes has come a long way. Steve Stewart Williams is a psychology professor who wrote the groundbreaking book The Ape That Understood the Universe and whose new book is A Billion Years of Sex Differences: How Evolution Shaped the Minds of Men and Women.

Steve joins Josh to explore the science of the sexes, from aggression to promiscuity to parenting, and what recent research reveals about how, and why, men and women behave the way we do.