Archer presents a comprehensive account of between-sex aggression from an evolutionary perspective built on sexual selection theory. We appreciate Archer's argument that sex differences in reproductive strategy are responsible for sexual conflict and for between-sex aggression. Sexual selection explains sex differences in aggression, in general. We contend, however, that there is a particular area of work that deserves more attention in research on violence in intimate relationships. There is a large body of research investigating men's partner-directed violence as an evolved solution to the adaptive problems of female infidelity and paternity uncertainty.

Over the course of human evolutionary history, men have faced the adaptive problem of female sexual infidelity and subsequent cuckoldry – or the unwitting investment in genetically unrelated offspring. The reproductive costs of cuckoldry, including loss of time, energy, resources, and alternative mating opportunities are potentially so great that men are hypothesized to have evolved psychological mechanisms that function to motivate anti-cuckoldry tactics. The problem of paternity uncertainty is hypothesized to have selected for the emotion of male sexual jealousy, which in turn motivates men's anti-cuckoldry tactics such as nonviolent and violent mate retention behaviors. Considerable evidence indicates that men's perceptions of their female partner's infidelity predict men's partner-directed insults, sexual coercion, and partner-directed violence.

Male sexual jealousy is one of the most frequently cited causes of men's partner-directed violence, both physical and sexual (e.g., Buss Reference Buss2000; Daly & Wilson Reference Daly and Wilson1988; Daly et al. Reference Daly, Wilson and Weghorst1982; Dobash & Dobash Reference Dobash and Dobash1979; Dutton Reference Dutton1998; Frieze Reference Frieze1983; Gage & Hutchinson Reference Gage and Hutchinson2006; Russell Reference Russell1982; Walker Reference Walker1979). The frequency with which men perform nonviolent mate retention behaviors predicts the frequency with which they inflict physical violence against their partners, arguably because both classes of behavior are outputs of sexual jealousy (Shackelford et al. Reference Shackelford, Goetz, Buss, Euler and Hoier2005a). Men who directly accuse their partners of sexual infidelity also are more likely to inflict partner-directed violence (Kaighobadi et al. Reference Kaighobadi, Starratt, Shackelford and Popp2008).

Sexual coercion also is hypothesized to function as an anti-cuckoldry tactic (Lalumière et al. Reference Lalumière, Harris, Quinsey and Rice2005; Thornhill & Thornhill Reference Thornhill and Thornhill1992; Wilson & Daly Reference Wilson, Daly, Barkow, Cosmides and Tooby1992; see also Goetz & Shackelford Reference Goetz and Shackelford2006). Instances of forced in-pair copulation (FIPC) have been documented in avian species that form long-term pair-bonds (Bailey et al. Reference Bailey, Seymour and Stewart1978; Barash Reference Barash1977; Birkhead et al. Reference Birkhead, Hunter and Pellatt1989; Cheng et al. Reference Cheng, Burns and McKinney1983; Goodwin Reference Goodwin1955; McKinney et al. Reference McKinney, Cheng, Bruggers and Smith1984). FIPC is hypothesized to be a form of post-copulatory male-male competition – that is, a sperm-competition tactic (Barash Reference Barash1977; Cheng et al. Reference Cheng, Burns and McKinney1983; Lalumière et al. Reference Lalumière, Harris, Quinsey and Rice2005; McKinney et al. Reference McKinney, Cheng, Bruggers and Smith1984), because it often follows a female partner's extra-pair copulation or intrusions by rival males (e.g., Bailey et al. Reference Bailey, Seymour and Stewart1978; Barash Reference Barash1977; Birkhead et al. Reference Birkhead, Hunter and Pellatt1989; Cheng et al. Reference Cheng, Burns and McKinney1983; Goodwin Reference Goodwin1955; McKinney et al. Reference McKinney, Derrickson and Mineau1983; McKinney & Stolen Reference McKinney and Stolen1982; Valera et al. Reference Valera, Hoi and Kristin2003). Sperm competition occurs when a female copulates with and is inseminated by more than one male in a sufficiently brief period of time (Parker Reference Parker1970). Thus, by forcing the female to copulate shortly after the increased risk of insemination by a rival, males place their sperm in competition with any sperm deposited into their partner by a rival male (Birkhead et al. Reference Birkhead, Hunter and Pellatt1989; Cheng et al. Reference Cheng, Burns and McKinney1983).

Observations of sperm competition in nonhuman species offer a framework with which to consider similar adaptations in humans, who also form long-term socially (but not genetically) monogamous pair-bonds. Recent evidence suggests that sperm competition has been a recurrent feature of human evolutionary history and that men have physiological and psychological mechanisms that may have evolved to solve related adaptive problems (Baker & Bellis Reference Baker and Bellis1993; Gallup et al. Reference Gallup, Burch, Zappieri, Parvez, Stockwell and Davis2003; Goetz et al. Reference Goetz, Shackelford, Weekes-Shackelford, Euler, Hoier, Schmitt and LaMunyon2005; Kilgallon & Simmons Reference Kilgallon and Simmons2005; Pound Reference Pound2002; Shackelford & Goetz Reference Shackelford and Goetz2007; Shackelford & Pound Reference Shackelford and Pound2006; Shackelford et al. Reference Shackelford, LeBlanc, Weekes-Shackelford, Bleske-Rechek, Euler and Hoier2002; Reference Shackelford, Pound and Goetz2005b; Smith Reference Smith and Smith1984). It has been hypothesized that, by forcing their partners to have sex, men who are suspicious of their partner's infidelity introduce their own sperm into their partner's reproductive tract and thereby decrease the risk of cuckoldry. Thornhill and Thornhill (Reference Thornhill and Thornhill1992) argued that women who resist or avoid copulating with their partners might thereby be signaling to their partners a recent sexual infidelity; hence, forced copulation might function to decrease men's paternity uncertainty. And the fact that rape of a woman is more likely to occur during or after a breakup (when men's concerns about women's infidelities are greatest) may provide preliminary support for this hypothesis (see Thornhill & Thornhill Reference Thornhill and Thornhill1992). A number of studies have documented a positive relationship between men's sexual jealousy and men's sexual coercion of their partners. For example, Frieze (Reference Frieze1983) and Gage and Hutchinson (Reference Gage and Hutchinson2006) found that men who sexually coerced their wives are more sexually jealous than men who did not. Previous research has found a direct positive relationship between men's suspicions and accusations of partner infidelity and men's sexual coercion of their partners (Starratt et al. Reference Starratt, Goetz, Shackelford and Stewart-Williams2008). In two studies securing data from men's self-reports and women's partner-reports, Goetz and Shackelford (Reference Goetz and Shackelford2006) found that men's sexual coercion correlated positively with women's past and future likelihood of engaging in sexual infidelity.

We recognize that sex differences in intimate partner violence can be explained by sex differences in reproductive strategies and by social roles, as Archer argues; however, men's partner-directed violence can be more specifically predicted by perceived risk of female infidelity and male sexual jealousy. A large body of empirical evidence supports the hypothesis that men's partner-directed sexual coercion and violence might sometimes be a product of evolved psychological mechanisms designed to prevent or punish female infidelity. The relevant evolved mechanisms interact with stable dispositions and situational factors to produce manifest behavior. Future research might benefit by using an evolutionary perspective to build models of intimate partner violence that include stable dispositions such as personality traits, environmental factors such as social roles, and situational factors such as perceived risk of partner infidelity.