Sex at Dawn
 The authors argue that human beings evolved in egalitarian hunter-gatherer bands in which sexual interaction was a shared resource, much like food, child care, group defense, and so on. In this, they agree to a degree with the work of Lewis H. Morgan who proposed in the 19th century that pre-agricultural humans lived in "primal hordes" in which property and paternity was communal. They think that much of evolutionary psychology has been conducted with a bias regarding human sexuality. The authors believe that the public and many researchers are guilty of the "Flintstonization" of hunter-gatherer society; that is to say projecting modern assumptions and beliefs onto earlier societies. Thus they think that there has been a bias to assuming that our species is primarily monogamous despite what they believe to be evidence to the contrary. They argue for example, that our sexual dimorphism, testicle size, female copulatory vocalization, appetite for sexual novelty, various cultural practices, and hidden female ovulation, among other factors strongly suggest a non-monogamous, non-polygynous history. The authors argue that mate selection was not the subject of much intragroup competition among pre-agricultural humans, as sex was neither scarce nor commodified; rather sperm competition was a more important paternity factor than sexual selection. This behaviour survives among certain existent hunter-forager groups that believe in partible paternity. The authors do not take an explicit position in the book regarding the morality of monogamy or alternative sexual behaviour in modern society, but argue that people should be made aware of our behavioral history.