Do Environmental Cues to Discovery Influence the Likelihood to Rape?

Research on men's sexual exploitation of women has documented that men's psychology tracks cues associated with the ease of women's exploitability. In the current studies, we examined a different class of cues hypothesized to aid men's use of sexually exploitative strategies: environmental cues to the likelihood of discovery. We defined likelihood of discovery as the perceived probability of identification when engaging in exploitative behavior (e.g., presence of others). We test the hypothesis that men's likelihood to rape increases when their perception of the likelihood of discovery is low in three studies. In Study 1, we conducted a content analysis of individuals' responses (N = 1,881) when asked what one would do if they could stop time or be invisible. Besides the "other" category whereby there were no specific category for nominated behaviors, the most nominated category included sexually exploitative behavior-representing 15.3% of reported behaviors. Both Studies 2 (N = 672) and 3 (N = 614) were preregistered manipulations of likelihood of discovery surreptitiously testing men's rape likelihood to rape across varying levels of discovery. We found men, compared to women, reported a statistically higher likelihood to rape in both Studies 2 and 3: 48% compared to 39.7% and 19% compared to 6.8%, respectively. Across Studies 2 and 3, we found no statistical effect of the likelihood of discovery on participants' likelihood to rape. We discuss how the presence of one's peers may provide social protection against the costs of using an exploitative sexual strategy if a perpetrator is caught.

Is the Vertical-Horizontal Illusion a Byproduct of the Environmental Vertical Illusion?

The vertical-horizontal illusion is the overestimation of a vertical line compared to a horizontal line of the same length. Jackson and Cormack (2007) proposed that the vertical-horizontal illusion might be a byproduct of the mechanisms that generate the environmental vertical illusion, which is the tendency to overestimate vertical distances (i.e., heights) relative to horizontal distances the same length. In our study, 326 undergraduate participants stood atop an 18.6-meter parking structure and estimated both the height of the structure and the horizontal distance of a target placed 18.6 meters away, using a moveable horizontal target across the length of the structure. Participants also completed a vertical-horizontal illusion task by drawing a horizontal line below a 9.1 cm vertical line. We correlated vertical distance estimates with vertical line estimates to test Jackson and Cormack's byproduct hypothesis. This hypothesis was very weakly-if at all-supported by the data: Participants' overestimations in the vertical-horizontal illusion task explained 1% of the variance associated with their overestimations in the environmental vertical illusion task. Additionally, to test whether the environmental vertical illusion is impervious to explicit awareness, a random half of our participants were advised to be mindful that people tend to overestimate heights. The results supported our second hypothesis: Even when participants were made aware of the environmental vertical illusion, they still reliably overestimated heights. Discussion addressed implications for the robustness of the environmental vertical illusion (e.g., treatment of those with acrophobia).

The implicit rules of combat.

Conspecific violence has been pervasive throughout evolutionary history. The current research tested the hypotheses that individuals implicitly categorize combative contexts (i.e., play fighting, status contests, warfare, and anti-exploitative violence) and use the associated contextual information to guide expectations of combative tactics. Using U.S. and non-U.S. samples, Study 1 demonstrated consistent classification of combative contexts from scenarios for which little information was given and predictable shifts in the acceptability of combative tactics across contexts. Whereas severe tactics (e.g., eye-gouging) were acceptable in warfare and anti-exploitative violence, they were unacceptable in status contests and play fights. These results suggest the existence of implicit rules governing the contexts of combat. In Study 2, we explored the reputational consequences of violating these implicit rules. Results suggest that rule violators (e.g., those who use severe tactics in a status contest) are given less respect. These are the first studies to implicate specialized mechanisms for aggression that use contextual cues of violence to guide expectations and behavior.

Changes in sleep time and sleep quality across the ovulatory cycle as a function of fertility and partner attractiveness.

Research suggests that near ovulation women tend to consume fewer calories and engage in more physical activity; they are judged to be more attractive, express greater preferences for masculine and symmetrical men, and experience increases in sexual desire for men other than their primary partners. Some of these cycle phase shifts are moderated by partner attractiveness and interpreted as strategic responses to women's current reproductive context. The present study investigated changes in sleep across the ovulatory cycle, based on the hypothesis that changes in sleep may reflect ancestral strategic shifts of time and energy toward reproductive activities. Participants completed a 32-day daily diary in which they recorded their sleep time and quality for each day, yielding over 1,000 observations of sleep time and quality. Results indicated that, when the probability of conception was high, women partnered with less attractive men slept more, while women with more attractive partners slept less.

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.

Perceived risk of female infidelity moderates the relationship between objective risk of female infidelity and sexual coercion in humans (Homo sapiens).

Female extrapair copulation (EPC) can be costly to a woman's long-term romantic partner. If a woman has copulated recently with a man other than her long-term partner, her reproductive tract may contain the sperm of both men, initiating sperm competition (whereby sperm from multiple males compete to fertilize an egg). Should the woman become pregnant, her long-term partner is at risk of cuckoldry-investing unwittingly in offspring to whom he is not genetically related. Previous research in humans (Homo sapiens) and in nonhuman animals suggests that males have evolved tactics such as partner-directed sexual coercion that reduce the risk of cuckoldry. The current research provides preliminary evidence that mated men (n = 223) at greater risk of partner EPC, measured as having spent a greater proportion of time apart from their partner since the couple's last in-pair copulation, more frequently perform partner-directed sexually coercive behaviors. This relationship is moderated, however, by men's perceived risk of partner EPC, such that the correlation between the proportion of time spent apart since last in-pair copulation and sexually coercive behaviors remains significant only for those men who perceive themselves to be at some risk of partner EPC. Discussion addresses limitations of this research and highlights directions for future research investigating the relationship between female EPC and men's partner-directed sexual coercion.

The evolutionary psychology of violence.

This paper reviews theory and research on the evolutionary psychology of violence. First, I examine evidence suggesting that humans have experienced an evolutionary history of violence. Next, I discuss violence as a context-sensitive strategy that might have provided benefits to our ancestors under certain circumstances. I then focus on the two most common forms of violence that plague humans -violence over status contests and intimate partner violence- outlining psychological mechanisms involved in each. Finally, I suggest that greater progress will be made by shifting the study from contexts to mechanisms.

The evolutionary psychology of violence / La psicología evolucionista de la violencia

This paper reviews theory and research on the evolutionary psychology of violence. First, I examine evidence suggesting that humans have experienced an evolutionary history of violence. Next, I discuss violence as a context-sensitive strategy that might have provided benefits to our ancestors under certain circumstances. I then focus on the two most common forms of violence that plague humans -violence over status contests and intimate partner violence- outlining psychological mechanisms involved in each. Finally, I suggest that greater progress will be made by shifting the study from contexts to mechanisms (AU)

Este artículo revisa la teoría y la investigación sobre la psicología evolucionista de la violencia. En primer lugar, se examinan las evidencias que sugieren que los seres humanos han experimentado una historia evolutiva de violencia. A continuación, se aborda la violencia como una estrategia sensible al contexto que podría haber producido beneficios a nuestros antepasados bajo determinadas circunstancias. Después nos centraremos en las dos formas más comunes de violencia que azotan a los seres humanos -la violencia durante disputas por estatus y la violencia de género- perfilando los mecanismos psicológicos implicados en ellas. Finalmente, se sugiere que se pueden derivar grandes progresos en este campo si se pasa de un estudio de los contextos a un estudio de los mecanismos (AU)

Sexual coercion in intimate relationships: a comparative analysis of the effects of women's infidelity and men's dominance and control.

Researchers studying the proximate (or immediate) causes of sexual coercion have proposed that partner rape is motivated by a man's attempt to dominate and control his partner and that this expression of power is the product of men's social roles. Researchers studying the ultimate (or evolutionary) causes, in contrast, have proposed that partner rape may function as an anti-cuckoldry tactic, with its occurrence related to a man's suspicions of his partner's sexual infidelity. In two studies, we collected data relevant to both perspectives to explore how these variables interact with men's sexual coercion in an intimate relationship. Regression analyses from Study 1 (self-reports from 256 men) and Study 2 (partner-reports from 290 women) indicated that men's sexual coercion of their partners was consistently predicted by female infidelity and men's controlling behavior, suggesting that both variables are necessary to explain men's sexual coercion. Discussion addressed limitations of the current research and highlighted the importance of integrating multiple levels of analysis when studying men's sexual coercion of their intimate partners.

Absence makes the adaptations grow fonder: proportion of time apart from partner, male sexual psychology, and sperm competition in humans (Homo sapiens).

Sperm competition occurs when the sperm of multiple males concurrently occupy the reproductive tract of a female and compete to fertilize an egg. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 237 men in committed, sexual relationships. As predicted, a man who spends a greater (relative to a man who spends a lesser) proportion of time apart from his partner since the couple's last copulation reported (a) greater sexual interest in his partner, (b) greater distress in response to his partner's sexual rejection, and (c) greater sexual persistence in response to his partner's sexual rejection. All effects were independent of total time since the couple's last copulation and the man's relationship satisfaction. Discussion addresses limitations of the current research and situates the current results within the broader comparative literature on adaptation to sperm competition.

Comparative evolutionary psychology of sperm competition.

A comparative evolutionary psychological perspective predicts that species that recurrently faced similar adaptive problems may have evolved similar psychological mechanisms to solve these problems. Sperm competition provides an arena in which to assess the heuristic value of such a comparative evolutionary perspective. The sperm competition that results from female infidelity and polyandry presents a similar class of adaptive problems for individuals across many species. The authors first describe mechanisms of sperm competition in insects and in birds. They suggest that the adaptive problems and evolved solutions in these species provide insight into human anatomy, physiology, psychology, and behavior. The authors then review recent theoretical and empirical arguments for the existence of sperm competition in humans and discuss proposed adaptations in humans that have analogs in insects or birds. The authors conclude by highlighting the heuristic value of a comparative evolutionary psychological approach in this field.

Adding insult to injury: development and initial validation of the Partner-Directed Insults Scale.

Women who are verbally abused by their intimate male partners suffer serious mental health consequences and often experience physical violence in their relationship. Despite the importance of studying verbal abuse, no previous research has investigated the specific content of the insults men use to derogate their partners. We present the development and initial validation of a new measure designed to assess the specific content of insults used by men against their intimate partners. In a preliminary study, we used feedback from battered women, along with a review of the relevant literature, to identify specific insults for inclusion in the Partner-Directed Insults Scale (PDIS). We administered the PDIS to a sample of United States participants (Study 1) and a sample of New Zealand participants (Study 2), allowing for a cross-national investigation of the specific insults that men use to derogate their partners. The results demonstrate the practical need for such a scale and provide evidence for the discriminant validity of the PDIS by documenting that men's use of insults predicts their use of controlling behaviors and physical violence.

Modern application of evolutionary theory to psychology: key concepts and clarifications.

Darwinian selection has become the centerpiece of biology, and in the past few decades many psychologists and anthropologists have recognized the value of using an evolutionary perspective to guide their work. With a focus on evolved psychological mechanisms and associated information processing features, evolutionary psychology has risen as a compelling and fruitful approach to the study of human psychology and behavior. In this article we review the instrument of evolution: natural selection, the products of evolution, and the impact of evolutionary thinking on modern psychological science. We conclude that as prejudicial barriers are overcome, as more evolutionary psychological work is conducted, and as hypothesized psychological mechanisms are substantiated in other disciplines, evolutionary psychology will emerge as the metatheory for psychology.

Mate guarding and frequent in-pair copulation in humans : Concurrent or compensatory anti-cuckoldry tactics?

Cuckoldry is an adaptive problem faced by parentally investing males of socially monogamous species (e.g., humans and many avian species). Mate guarding and frequent in-pair copulation (IPC) may have evolved as anti-cuckoldry tactics in avian species and in humans. In some avian species, the tactics are used concurrently, with the result that mate guarding behaviors and IPC frequency are correlated positively. In other avian species, the tactics are compensatory, with the result that mate guarding behaviors and IPC frequency are correlated negatively. The relationship between mate guarding and IPC frequency in humans is unknown. Avian males that use these tactics concurrently share with human males an inability to guard a female partner continuously during her peak fertile period. We hypothesized, therefore, that men's mate guarding and IPC frequency function as concurrent anti-cuckoldry tactics, resulting in a positive correlation between them. Study 1 (n=305) secured men's self-reports of mate guarding and IPC frequency. Study 2 (n+367) secured women's reports of their partners' mate guarding and IPC frequency. The concurrent tactics hypothesis was supported in both studies: Men's mate guarding and IPC frequency are correlated positively, and this association is not attributable to male age, female age, relationship satisfaction, relationship length, or time that the couple spends together. The Discussion section addresses potential limitations of this research and future research directions.

Sexual coercion and forced in-pair copulation as sperm competition tactics in humans.

Rape of women by men might be generated either by a specialized rape adaptation or as a by-product of other psychological adaptations. Although increasing number of sexual partners is a proposed benefit of rape according to the "rape as an adaptation" and the "rape as a by-product" hypotheses, neither hypothesis addresses directly why some men rape their long-term partners, to whom they already have sexual access. In two studies we tested specific hypotheses derived from the general hypothesis that sexual coercion in the context of an intimate relationship may function as a sperm competition tactic. We hypothesized that men's sexual coercion in the context of an intimate relationship is related positively to his partner's perceived infidelities and that men's sexual coercion is related positively to their mate retention behaviors (behaviors designed to prevent a partner's infidelity). The results from Study 1 (self-reports from 246 men) and Study 2 (partner-reports from 276 women) supported the hypotheses. The Discussion section addresses limitations of this research and highlights future directions for research on sexual coercion in intimate relationships.

Sex differences in sexual psychology produce sex-similar preferences for a short-term mate.

We explored aspects of men's and women's short-term sexual psychology as a function of a potential short-term partner's relationship status. A total of 209 men and 288 women reported how likely they would be to pursue a casual sexual relationship with an attractive member of the opposite sex who was (1) married, (2) not married but has casual sexual partners, or (3) not married and has no casual sexual partners. Guided by sperm competition theory, we predicted and found that men prefer short-term sex partners who are not already involved in relationships and hence present a relatively low risk of sperm competition. Because women sometimes use short-term sexual relationships to acquire long-term partners, we predicted and found that women prefer short-term sexual partners who are not already involved in relationships and hence present relatively greater promise as a potential long-term partner. Finally, across each of the three levels of the imagined partner's relationship status, men reported a greater likelihood than did women of pursuing a casual sexual relationship. Discussion addressed methodological limitations and directions for future work.

Men's sexual coercion in intimate relationships: development and initial validation of the Sexual Coercion in Intimate Relationships scale.

We report the development and initial validation of the Sexual Coercion in Intimate Relationships Scale (SCIRS), a measure designed to assess the prevalence and severity of sexual coercion in committed intimate relationships. We review existing measures of sexual coercion and discuss their limitations, describe the identification of the SCIRS items, perform a principal components analysis and describe the resulting three components, and present evidence for the convergent and discriminative validity of the SCIRS. Because sexual coercion in intimate relationships often takes the form of subtle tactics, the SCIRS items assess communicative tactics such as hinting and subtle manipulations in addition to tactics such as the use of physical force. The SCIRS provides researchers and clinicians with a valid, reliable, and comprehensive measure with which to study the dynamics of sexual coercion in intimate relationships.