In this blog post, I will examine one perspective on whether rape can be viewed as an evolutionary adaptation, based on the concepts of natural selection and adaptation.
The term “natural selection” is a concept used by Charles Darwin—who laid the foundation for evolutionary theory—in ‘On the Origin of Species’, and it remains one of the core concepts of evolutionary biology today. For natural selection to occur, a variety of traits must exist within a species, and through interaction with the surrounding environment, the traits most advantageous for survival and reproduction must be selected. Therefore, natural selection drives a species toward traits that are advantageous for survival in a given environment.
For example, let’s assume that a certain species possesses arbitrary traits A, B, and C. In this case, the number of individuals with each trait within the population will vary. If the environment in which this species lives changes to create conditions that are disadvantageous for traits A and B but advantageous for trait C, the number of individuals with traits A and B will decrease, while the number of individuals with trait C will increase. Eventually, the frequency of trait C within the population will gradually increase, and given sufficient time, trait C will come to account for an overwhelmingly higher proportion compared to the other traits. This phenomenon is called natural selection, and the state in which a specific trait is selected by nature is described as adaptation to the environment. Natural selection is the process by which the interaction between a species and its environment determines which traits will become more frequent within a population. Since the entity selecting the trait is not the species itself but the surrounding environment—that is, nature—natural selection is, in and of itself, a value-neutral process. In other words, from the species’ perspective, it cannot arbitrarily determine the direction of its own evolution.
Rape is a very serious crime classified as a violent crime alongside murder, arson, robbery, and kidnapping. While we encounter countless crimes in the news, it is easy to see that sexual violence crimes, in particular, continue to occur. Rape—the act of forcing sexual intercourse while disregarding the other person’s will—inflicts extreme psychological and physical harm on the victim, and its aftereffects often persist for a long time. For this reason, rape is regarded as one of the most inhumane crimes, and many countries around the world today are continuously strengthening their systems for punishing and managing sex offenders.
To put it simply, if rape were an adaptation formed through natural selection, the trait of rape would have had to have been advantageous for human survival and reproduction in the past. For this to be true, two premises are necessary. First, rape must be a trait. Second, rape must have a positive effect on human survival and reproduction. So, can rape truly be considered a trait? Generally, a trait in a living organism refers to its observable forms and attributes. Here, “observable” does not necessarily mean visible to the naked eye, but rather refers to characteristics that distinguish one individual from another. Therefore, even attributes that are not outwardly apparent, such as blood type, are defined as traits. From this perspective, it is possible to argue that rape can be defined as a trait because it is an observable behavioral attribute in humans.
The second premise concerns whether rape is a trait advantageous to human survival. In modern society, sexual intercourse is considered a normal relationship only when it occurs with the voluntary consent of both parties. In contrast, rape is a crime in which sexual intercourse is forced upon another person against their will through the use of violence, and it is subject to severe legal punishment. Legal punishment results in social and economic disadvantages, which can lead to outcomes detrimental to an individual’s survival and reproduction. Therefore, in modern society, it is difficult to view the act of rape as a trait advantageous for survival. From the perspective of natural selection, the environment surrounding individuals has shifted in a direction that is highly disadvantageous to those who commit rape. However, this fact alone does not allow us to conclusively determine that rape was not an adaptation in the past. From the perspective of this paper, the discussion proceeds on the premise that the act of rape may have persisted for a certain period because it served a function favorable to survival and reproduction in past human societies.
Specifically, to examine the claim that rape is a trait favorable to survival, we must consider both men and women since the divergence of modern humans. Given that the majority of rapists are men and the majority of victims are women, it is possible to interpret that rape served the function of increasing women’s likelihood of pregnancy, thereby contributing to population growth. From this perspective, it is argued that the act of rape contributed to the growth of the human population and, consequently, acted in a way that was advantageous for the species’ maintenance and survival. However, for women, once pregnancy occurs, their behavior is restricted for a long period until childbirth, and they must also bear the burden of child-rearing after giving birth. Therefore, women may tend to choose pregnancy only if the postpartum environment is stable, and it is likely that they behaved in a way that avoided indiscriminate pregnancies. In contrast, men did not face significant direct physical burdens even if pregnancy occurred after sexual intercourse; in environments where there was no strong legal punishment system like that of today, it is plausible that they adopted a strategy of increasing their reproductive potential by having sexual relations with more women.
According to Gottschall’s study, which surveyed 405 female rape victims aged 12 to 45, the pregnancy rate was 6.4%; excluding cases where contraception was used, it was reported to be approximately 8%. In contrast, the pregnancy rate per incident among couples engaging in regular sexual intercourse with the intent to conceive was found to be lower than this. Based on these results, the study explained that rape exhibits a relatively high probability of pregnancy per incident. However, these findings alone do not definitively conclude that rape is an evolutionary adaptation; subsequent studies have discussed various explanations, including the evolutionary byproduct hypothesis and the adaptation hypothesis. Therefore, these findings should be understood as a single case study.
It is difficult to categorize rape victims solely based on their gender. If the purpose of rape were to impregnate women, then rapes committed against individuals who cannot become pregnant would be difficult to fully explain using this rationale alone. Sexual violence against infants or the elderly serves as an example illustrating this point. Conversely, one could argue that mechanisms for selectively targeting women of specific age groups may not have been sufficiently developed in the past. From this perspective, it is possible to interpret the various forms of sexual crimes observed in modern society as the result of past behavioral patterns adapting to a changed environment. This article views rape as an observable behavioral trait and concludes that it is an adaptation, based on the possibility that it exerted a certain influence on reproduction in past human societies. However, this conclusion is a topic on which scholars in evolutionary psychology and evolutionary biology are deeply divided, and it is not yet accepted as an established academic consensus.
