Oral Sex, Semen Displacement, and Sexual Arousal: Testing the Ejaculate Adjustment Hypothesis

Male Indian Flying Foxes ( Pteropus giganteus) that spend more time performing oral sex on a female also spend more time copulating with her. In humans, men who spend more time copulating with their regular partner also perform more “semen-displacing” copulatory behaviors (e.g., deeper, more vigorous penile thrusting). We investigated whether men who spend more time performing oral sex on their regular partner also spend more time copulating with her and perform more semen-displacing copulatory behaviors. We proposed and tested the ejaculate adjustment hypothesis for men's copulatory behaviors: Men adjust their copulatory behaviors to increase their sexual arousal and consequent ejaculate quality, thereby increasing their chances of success in sperm competition. Two hundred and thirty-three men in a committed, heterosexual relationship responded to questions about their copulatory behavior and sexual arousal during their most recent sexual encounter with their long-term partner. The results indicated that men who spend more time performing oral sex on their partner also spend more time copulating with her, perform more semen-displacing copulatory behaviors, and report greater sexual arousal. We discuss limitations to the current research and highlight the heuristic value of sperm competition theory for understanding human sexual behaviors.

The relationship between objective sperm competition risk and men's copulatory interest is moderated by partner's time spent with other men

Men who spend a greater proportion of time apart from their female partner since the couple's last copulation are at greater "objective" sperm competition risk. We propose a novel cue to sperm competition risk: the time she spends with her male friends. Four hundred and twenty men in a committed, heterosexual, sexual relationship completed a questionnaire. The results indicate that men at greater objective sperm competition risk report less time desired until the couple's next copulation, greater interest in copulating with their partner, and greater anger, frustration, and upset in response to their partner's sexual rejection, but only among men whose partner spends more time with her male friends. These results remain after controlling statistically for the participant's age and their partner's age. We discuss limitations of the current research, and discuss how research in human sperm competition can inform social issues, including men's partner-directed sexual coercion.

An introduction to comparative evolutionary psychology

Previously we (Vonk and Shackelford, 2012, in press) proposed an integration of comparative psychology and evolutionary psychology into a new field of "comparative evolutionary psychology." This integrative discipline incorporates principles from ethology, ecology, biology, anthropology, and psychology, broadly defined. We present in this special issue a collection of original empirical and theoretical review articles in which leading researchers propose ways to successfully integrate comparative and evolutionary approaches within their particular areas of study. We showcase the key contributions of these articles and highlight several empirical and theoretical challenges, as well as key future directions, for comparative evolutionary psychology.

An Introduction to Comparative Evolutionary Psychology

Previously we ( Vonk and Shackelford, 2012 , in press) proposed an integration of comparative psychology and evolutionary psychology into a new field of “comparative evolutionary psychology.” This integrative discipline incorporates principles from ethology, ecology, biology, anthropology, and psychology, broadly defined. We present in this special issue a collection of original empirical and theoretical review articles in which leading researchers propose ways to successfully integrate comparative and evolutionary approaches within their particular areas of study. We showcase the key contributions of these articles and highlight several empirical and theoretical challenges, as well as key future directions, for comparative evolutionary psychology.

Is cunnilingus-assisted orgasm a male sperm-retention strategy?

We secured data from 243 men in committed, sexual, heterosexual relationships to test the sperm retention hypothesis of oral sex. We predicted that, among men who perform cunnilingus on their partner, those at greater risk of sperm competition are more likely to perform cunnilingus until their partner achieves orgasm (Prediction 1), and that, among men who ejaculate during penile-vaginal intercourse and whose partner experiences a cunnilingus-assisted orgasm, ejaculation will occur during the brief period in which female orgasm might function to retain sperm (Prediction 2). The results support Prediction 1 but not Prediction 2. We discuss limitations of the current research and discuss how these results may be more consistent with alternative hypotheses regarding female orgasm and oral sex.

Is Cunnilingus-Assisted Orgasm a Male Sperm-Retention Strategy?

We secured data from 243 men in committed, sexual, heterosexual relationships to test the sperm retention hypothesis of oral sex. We predicted that, among men who perform cunnilingus on their partner, those at greater risk of sperm competition are more likely to perform cunnilingus until their partner achieves orgasm (Prediction 1), and that, among men who ejaculate during penile-vaginal intercourse and whose partner experiences a cunnilingus-assisted orgasm, ejaculation will occur during the brief period in which female orgasm might function to retain sperm (Prediction 2). The results support Prediction 1 but not Prediction 2. We discuss limitations of the current research and discuss how these results may be more consistent with alternative hypotheses regarding female orgasm and oral sex.

Human Violence and Evolutionary Consciousness

The evolution and development of adaptations results from the gradual selection of traits that enable organisms to acquire and maintain resources needed for survival and reproduction. We argue that instances of individual, regional, and global violence are rooted in our adaptations to seek, acquire, maintain, and utilize limited resources, regardless of whether such adaptations are currently successful at doing so. However, violence is not the only strategy employed by organisms to acquire resources; cooperation, reciprocity, and social bonding are behaviors that likewise may prove useful in this endeavor. We speculate about how individual adaptations and their byproducts may interact with the adaptations of other individuals and with societal and cultural phenomena, both violently and nonviolently. Finally, we discuss how individual decisions can affect higher level regional and global violence. Individual decisions carry moral weight for the individual in question and for society as a whole. We argue that individual decisions and behaviors can have far-reaching consequences on the well-being of others and that an evolutionary consciousness may help us to understand the effects of our personal choices on the existence of individual and group-level violence.

Do women pretend orgasm to retain a mate?

The current study tested the hypothesis that women pretend orgasm as part of a broader strategy of mate retention. We obtained self-report data from 453 heterosexual women (M age, 21.8 years) in a long-term relationship (M length, 32.8 months) drawn from universities and surrounding communities in the southeastern United States. The results indicated that (1) women who perceived higher risk of partner infidelity were more likely to report pretending orgasm, (2) women who reported greater likelihood of pretending orgasm also reported performing more mate retention behaviors, and (3) women's perceptions of partner infidelity risk mediated the relationship between pretending orgasm and the performance of cost-inflicting mate retention behaviors, such as Intersexual Negative Inducements ("Flirted with someone in front of my partner") and Intrasexual Negative Inducements ("Yelled at a woman who looked at my partner"). Thus, pretending orgasm may be part of a broader strategy of mate retention performed by women who perceive higher risk of partner infidelity.

Why Can't We All Just Get Along? Evolutionary Perspectives on Violence, Homicide, and War

We review and discuss the evolutionary psychological literature on violence, homicide, and war in humans and nonhumans, and in doing so argue that an evolutionary perspective can substantially enhance our understanding of these behaviors. We provide a brief primer on evolutionary psychology, describing the basic tenets of the field. The theories of sexual selection and parental investment are explained and subsequently used to highlight the evolutionary logic underlying the use of violence by humans and other animals. Our examination of violent behavior begins with a focus on nonhuman animals, reviewing the different contexts in which violence occurs and discussing how an evolutionary perspective can explain why it occurs in these contexts. We then examine violence in humans and illustrate the similarities and differences between human and nonhuman violence. Finally, we summarize what an evolutionary perspective can offer in terms of understanding violence, homicide, and war, and discuss directions for future research.

Human sexual conflict from molecules to culture

Coevolutionary arms races between males and females have equipped both sexes with mutually manipulative and defensive adaptations. These adaptations function to benefit individual reproductive interests at the cost of the reproductive interests of opposite-sex mates, and arise from evolutionary dynamics such as parental investment (unequal reproductive costs between the sexes) and sexual selection (unequal access to opposite-sex mates). Individuals use these adaptations to hijack others' reproductive systems, psychological states, and behaviors--essentially using other individuals as extended phenotypes of themselves. Such extended phenotypic manipulation of sexual rivals and opposite-sex mates is enacted by humans with the aid of hormones, pheromones, neurotransmitters, emotions, language, mind-altering substances, social institutions, technologies, and ideologies. Furthermore, sexual conflict may be experienced at an individual level when maternal genes and paternal genes are in conflict within an organism. Sexual conflict may be physically and emotionally destructive, but may also be exciting and constructive for relationships. By extending the biological concept of sexual conflict into social and cultural domains, scholars may successfully bridge many of the interdisciplinary gaps that separate the sciences from the humanities.

Human Sexual Conflict from Molecules to Culture

Coevolutionary arms races between males and females have equipped both sexes with mutually manipulative and defensive adaptations. These adaptations function to benefit individual reproductive interests at the cost of the reproductive interests of opposite-sex mates, and arise from evolutionary dynamics such as parental investment (unequal reproductive costs between the sexes) and sexual selection (unequal access to opposite-sex mates). Individuals use these adaptations to hijack others' reproductive systems, psychological states, and behaviors—essentially using other individuals as extended phenotypes of themselves. Such extended phenotypic manipulation of sexual rivals and opposite-sex mates is enacted by humans with the aid of hormones, pheromones, neurotransmitters, emotions, language, mind-altering substances, social institutions, technologies, and ideologies. Furthermore, sexual conflict may be experienced at an individual level when maternal genes and paternal genes are in conflict within an organism. Sexual conflict may be physically and emotionally destructive, but may also be exciting and constructive for relationships. By extending the biological concept of sexual conflict into social and cultural domains, scholars may successfully bridge many of the interdisciplinary gaps that separate the sciences from the humanities.