Nancy Wilmsen Thornhill

Human rape: An evolutionary analysis

Abstract Human evolutionary history was apparently one of polygyny. Polygyny favors the use of different reproductive options by human males with different competitive abilities. These options or alternatives collectively represent a single conditional strategy; which alternatives are employed depend on conditions encountered during a mans life history. It is hypothesized that human rape is an evolved facultative alternative that is primarily employed when men are unable to complete for resources and status necessary to attract and reproduce successfully with desirable mates. According to this hypothesis males that cannot effectively compete may employ rape as the only behavioral alternative, or depending on circumstances of relative status and family composition, they may incorporate rape into a repertoire of other behavioral patterns, including low commital pairbonding with one or more females and/or investing available resources toward sisters offspring. The evolutionary view of rape we propose is completely testable. The view provides predictions about the rapists and victims behavior and about rape laws and taboos, several of which we attempt to test. This study indicates that an evolutionary view promises considerable understanding of rape and related phenomena.

The evolutionary psychology of men's coercive sexuality

Psychological adaptation underlies all human behavior. Thus, sexual coercion by men could either arise from a rape-specific psychological adaptation or it could be a side-effect of a more general psychological adaptation not directly related to rape. Determining the specific environmental cues that mens brains have been designed by selection to process may help us decide which these rival explanations is correct. We examine six testable predictions against existing data: (1) Both coercive and noncoercive will be associated with high levels of sexual arousal and performance in men. (2) Achieving physical control of a sexually unwilling woman will be sexually arousing to men. (3) Young men will be more sexually coercive than older men. (4) Men of low socioeconomic status will likewise be more sexually coercive. (5) A mans motivation to use sexual coercion will be influenced by its effects on social image. (6) Even in long-term relationships men will be motivated to use coercion when their mates show a lack of interest in resistance to sex because these are interpreted as signs of sexual infidelity. Current data support all six predictions and are hence consistent with the rape-specific hypothesis, but this does not eliminate the side-effect hypothesis, which is likewise compatible with the findings, as well as with the further evidence that forced matings increased the fitness of ancestral males during human evolution. We suggest some research that may help decide between the two hypotheses.

The evolutionary significance of incest rules

Abstract Evolutionary theory predicts that humans should avoid incest because the behavior depresses individual fitness through production of defective offspring. Selection for avoidance of close-kin mating has resulted in a developmental mechanism that promotes voluntary incest avoidance. If avoided, why are social rules constructed in most cultures to regulate incest? The suggestion in this article is that incest do not regulate close-kin mating, but instead regulate inbreeding between more distant kin and sexual relations between nonkin. Inbreeding (e.g., cousin marriage) is hypothesized to be regulated because if it occurs, it can concentrate wealth and power within families threatening the powerful positions of rulers in the society. The hypothesis was supported using a worldwide sample of 129 societies, whereas two other alternative hypotheses (one dealing with coadapted genomes, and the other with sexual reproduction and host/ parasite coevolution), were not.

Female Primate Sexual Behavior and Conception: Are There Really Sperm to Spare? [and Comments and Reply]

Female primates are noted for a varied and assertive pattem of sexual activity that does not necessarily correspond with conception. In general, they mate with multiple partners, or repeatedly with one male, even during periods when conception is unlikely. This pattem requires explanation because females incur costs for nonconceptive matings by interacting with potentially aggressive males and limiting the energy they can expend in foraging or caring for present offspring. Previous explanations of female sexual behavior have concentrated on postnatal benefits to females and their infants. That is, females in polygynous groups may mate with multiple partners to confuse paternity, avoid male-imposed infanticide, and receive patemal care from many males. An alternative explanation is that females who mate frequently improve their chances of conception with multiple inseminations and concurrently deplete the sperm supplies available to competing females. Under certain conditions, such as a low male: female sex ratio in seasonally breeding roups, sperm can be a relatively limited resource. Thus some females may be able to improve their reproductive success by frequent matings, even during nonfertile periods. The implications of this hypothesis for the evolution of human female sexual behavior and concealed ovulation are discussed.

An evolutionary analysis of psychological pain following human (Homo sapiens) rape. IV, The effect of the nature of the sexual assault

Mental pain is hypothesized to manifest an adaptation for analyzing and coping with social problems that would have reduced inclusive fitness in human (Homo sapiens) evolutionary history. We examined this hypothesis in the psychological pain of 790 rape victims. Reproductive-aged and postreproductive-aged victims were more likely than prereproductive-aged victims to have experienced vaginal intercourse and to have had sperm present in the reproductive tract. As predicted, vaginal intercourse constituted the most psychologically devastating form of sexual assault for reproductive-aged women. Nonreproductive-aged victims were not more traumatized by vaginal rapes. When rapes included ejaculation in the victims reproductive tract, reproductive-aged victims may have been more traumatized. These results suggest that the psychology that regulates mental pain processes information about the nature of the sexual act in the event of a womans rape.