Why are men, like other primate males, usually the aggressors and risk takers? Why do women typically have fewer sexual partners? In Why Sex Matters, Bobbi Low ranges from ancient Rome to modern America, from the Amazon to the Arctic, and from single-celled organisms to international politics, to show that these and many other questions about human behavior largely come down to evolution and sex. More precisely, as she shows in this uniquely comprehensive and accessible survey of behavioral and evolutionary ecology, they come down to the basic principle that all organisms evolved to maximize their reproductive success and seek resources to do so, but that sometimes cooperation and collaboration are the most effective ways to succeed. This newly revised edition has been thoroughly updated to include the latest research and reflect exciting changes in the field, including how our evolutionary past continues to affect our ecological present.