Introduction
1. Splitting the Lark: The Origins of Sex
2. Pinpointing the Difference: Comparing Male and Female Brains
3. Heart to Heart: Sex Differences in Emotion
4. Perfect Partners: The Monogamy Puzzle
5. The Second Date: Inquiries into Sexual Orientation
6. The Big T: Defining Testosterone
7. The Cycle Game: Biology and Estrogen
8. Counterstrikes: Love, Lust, and Rape
9. Once Divided: Power and Gender Biology
Notes
Index