Demonic Males begins by explaining that humans, chimpanzees, bonobos, gorillas and orangutans are a group of genetically related great apes, that humans are genetically closer to chimps than chimps are to gorillas, and that chimps and bonobos are most closely genetically related. After speculating about what enabled humans' ancestors to leave the rainforest (the use of roots as sources of water and food), Demonic Males next provides a catalog of the types of violence practiced by male chimpanzees (intra-group hierarchical violence, violence against females and extra-group murdering raids). The high incidence of rape by non-alpha male orangutans and infanticide by male gorillas are also cited as examples of our mutual genetic heritage.
The authors present chimp society as extremely patriarchal, in that no adult male chimpanzee is subordinate to any female of any rank. They present evidence that most dominant human civilizations have always been likewise behaviorally patriarchal, and that male humans share male chimpanzees' innate propensity for dominance, gratuitous violence, war, rape and murder. They claim that the brain's prefrontal cortex is also a factor, as humans have been shown experimentally to make decisions based both on logic and prefrontal cortex-mediated emotion.
In the chapter "The Peaceful Ape," the authors contrast chimpanzee behaviors with those of the bonobo, presenting logical biological reasons for the more pacific (although also aggressive and antagonistic) behaviors of the latter. Reasons include a bonobo female social organization that doesn't tolerate male aggression, the invisibility of bonobo ovulation (in chimps, ovulation has both olfactory and genital swelling manifestations, leading to ferocious male competition for mating), and overall social organization, whereby male bonobos don't form alliances as male chimps do. (Contested: Heisterman et al (1996) show that female bonobos display sexual swellings which they considered to be a reliable indicator of probability of ovulation).
The authors consider male violence to be evolutionarily undesirable and morally reprehensible (explicitly detailing the Hutu-Tutsi cross-genocides in Africa's Great Ape habitats, and citing Charlotte Perkins Gilman's female utopian novel Herland ), and argue that the advent of modern weapons such as nerve gas and atomic bombs threaten our collective future. Like Steven Pinker's The Better Angels of Our Nature: Why Violence Has Declined (2012), which makes the case that violence has been decreasing in human society over time, Demonic Males makes the case that human males are genetically predisposed to violence, but that our species also has the intellectual capacity to override this flaw if we recognize that it is in our survival interest to do so.
In a political interpretation of Demonic Males, biologist Philip Regal says that the book is partly an attack on the deconstructivist feminist theory that male violence is a purely social construct. Regal also considers the book to be "a broadside against the old utopian dreams of Atlantis, Eden, Elysium, a Golden Age, Romantic paintings, and the late Margaret Mead" which imagined human beings as naturally peaceful.
The New York Times called it "enjoyable and easy to read" and said it "belongs to the emerging genre of serious scientific books that have something to say about questions of interest to many people, not just to specialists".
- Daniel Pinchbeck, "Men, Monkeys And Mayhem ", The Washington Post, November 17, 1996, https://www.washingtonpost.com/wp-srv/style/longterm/books/reviews/demonicmales.htm
- Mark Ridley, "Going Ape", The New York Times, October 27, 1996, https://www.nytimes.com/1996/10/27/books/going-ape.html?pagewanted=all&src=pm
- Regal, Philip J. 1996. Review of Demonic Males: Apes and the Origins of Human Violence by Richard Wrangham and Dale Peterson. Quarterly Review of Biology 73:473-476. ("Violence and Sex") online at https://web.archive.org/web/20080513092541/http://www.tc.umn.edu/~regal001/demonic.htm
Heistermann, M., Mohle, U., Vervaecke, H., van Elsacker, L., Hodges, J.K. (1996) ‘Application of Urinary and Fecal Steroid Measurements for Monitoring Ovarian Function and Pregnancy in the Bonobo (Pan paniscus) and Evaluation of Perineal Swelling Patterns in Relation to Endocrine Events’. In Biology of Reproduction, 55, 844-853