Organisms live their lives in a staggering diversity of ways. Not only ecologically, but in the very patterns of their lives, there is great diversity. Across nonhuman species, there are asexual species, species with one sex, two sexes, and more than two sexes. There are species in which a single individual is two sexes, either concurrently or sequentially; species that live only minutes and species that live for centuries; species that breed once and die and species that breed repeatedly; species that have single young and species that lay thousands of eggs at a time. It is easy for those of us who specialize in human behavior and evolution to remain unaware of the sheer scope of this diversity. Yet human life histories are unusual, and occasionally unique, in ways that are instructive in the context of all this diversity. This chapter describes the ways in which humans are typical, and unusual primates, and uses natural selection theory to explore why we differ in the particular ways we do.