Book Review Sexual Coercion in Primates and Humans: An Evolutionary Perspective on Male Aggression

Research on sexual coercion from an evolutionary perspective has been given considerable attention in both the human and nonhuman literatures. Sexual Coercion in Primates and Humans: An Evolutionary Perspective on Male Aggression Against Females represents the first synthesis on primates, though reviews on sexual coercion in a wider variety of species have been published elsewhere (e.g., Lalumière, et al., 2005). This book is organized into five sections: (I) Introduction and theory; (II) Sexual coercion and mate guarding in nonhuman primates; (III) Sexual coercion and mate guarding in humans; (IV) Female counterstrategies; and (V) Summary and conclusions. Section I includes three introductory chapters on defining, studying, and explaining sexual coercion. In Chapter 1, Muller, Kahlenberg, and Wrangham introduce readers to a widely used definition of sexual coercion: ‘‘use by a male of force or threat of force that functions to increase the chances that a female will mate with him at a time when she is likely to be fertile, and to decrease the chances that she will mate with other males, at some cost to the female’’ (Smuts and Smuts, 1993: p. 2, 3). This definition is then used to specify a taxonomy of coercion that includes direct coercion (forced copulation, harassment, and intimidation); indirect coercion (or coercive mate guarding that includes herding, punishment, and sequestration); and infanticide. Although this definition and taxonomy limits the scope of sexual coercion (i.e., it focuses on coercion as an adaptive response to sexual conflict, not as a byproduct or a disorder), one of the virtues of this book is its consistent use of this definition and taxonomy throughout most chapters. Two recent and important theoretical developments treat sexual coercion as a third component of sexual selection, alongside intrasexual and intersexual selection (Andersson and Iwasa, 1996), and using sexual conflict theory to account for phenotypic variation between the sexes (Arnqvist and Rowe, 2005). In Chapter 2, WatsonCapps describes how the sexual coercion and sexual conflict literatures rarely coincide and then links them by describing how ‘‘sexual coercion is one mechanism of sexual selection, brought about by sexual conflict over when to mate and whom to mate with’’ (p. 32). Watson-Capps uses sexual conflict theory to establish constraints under which sexual coercion as an adaptation could evolve. For example, sexual coercion must exert fitness costs to the female. In Chapter 3, Clarke, Pradhan, and van Schaik use mathematical modeling to focus on infanticide as a primary selection pressure among primates leading to sexual coercion. By focusing on mathematical modeling, they provide a unique contribution to this alternative method of studying sexual coercion. Section II includes seven chapters that review research and present new data on sexual coercion across several nonhuman primate species. These chapters continue to use the same definition and taxonomy of coercion established in Section I, and it is easy to follow how sexual conflict has led to various manifestations of sexual coercion across a variety of primates, including orangutans (Chapter 4), mountain gorillas (Chapter 5), chacma baboons (Chapter 6), spider monkeys (Chapter 7), chimpanzees (Chapter 8), and hamadryas baboons (Chapter 10). Comparisons between species are also made. For example, despite the convergence of social behavior in dolphins and chimpanzees, Connor and Vollmer describe in Chapter 9 how differences in sexual coercion could have emerged. These chapters provide sufficient theoretical explanations, but their conclusions are largely based on small samples and reanalysis of data collected for projects unrelated to sexual coercion. These chapters should therefore be treated as a foundation for more systematic experimental work on primate coercion. For example, experiments could be used to test the hypothesis proposed in Chapter 10 that aggression functions by conditioning females to remain sexually faithful rather than by signaling strength. In addition to providing alternative explanations for the presence of coercion (e.g., see Chapter 8), the authors clearly outline their recommendations for future research. With the exception of Chapters 11 and 13, readers may find Section III incomplete and even inconsistent with the evolutionary theme of this book. In Chapter 13, Novak and Hatch provide an interesting discussion on using craniofacial trauma as an alternative way to study sexual coercion and conflict between species. Their data comparing humans and chimpanzees provide an important demonstration of this approach. In Chapter 11, Wilson and Daly offer a promising start to the section on humans by elucidating how nonsexual violence in mating dyads functions by preventing cuckoldry. Unfortunately, this is the only chapter on humans that was consistent with the taxonomy of sexual coercion introduced in Chapter 1. In Chapter 12, Rodseth and Novak propose politics as an alternative explanation for sexual coercion in humans, yet they do not provide a very clear definition of politics, making the entire chapter difficult to follow. They introduce ‘‘private life’’ as an aspect of human ecology that may be related to sexual coercion, but the chapter lacks theoretical consistency with other chapters and fails to propose hypotheses in empirically testable ways. Instead, the chapter draws heavily from anthropological anecdotes and uses a type of confusing language sometimes found in the social sciences, such as ‘‘violence against women is often an ideological symbol rather than a customary practice’’ (p. 303). In Chapter 14, Thompson purportedly introduces a revision to evolutionary perspectives on human rape. The ‘‘revision,’’ however, is really a critique of a particular hypothesis of sexual coercion, mate-deprivation, and proposal of another hypothesis on acquaintance rape. This chapter represents a missed opportunity to review and critically appraise the many evolutionary hypotheses on rape in humans, such as Malamuth’s confluence model (1996), Lalumiere et al.’s three path model (2005), the cuckoldry risk hypothesis of partner rape (e.g., Camilleri and Quinsey, 2009), and evolutionary understanding of sexual disorders (e.g., Quinsey, 2003; in press). Unfortunately, Thompson gives the impression that mate deprivation is the only adaptive hypothesis of human rape and prematurely dismisses it by falsely asserting that AMERICAN JOURNAL OF HUMAN BIOLOGY 00:000–000 (2010)