In this blog post, we examine the various academic debates surrounding the origins of rape behavior and explore which explanation—instinct or social learning—provides a more compelling account.
The dictionary definition of rape is the crime of forcing someone to have sexual intercourse. Because rape inflicts severe harm on victims that goes beyond mere physical injury, academic discussions about its causes have persisted for a long time. Identifying the causes of rape could lead to more effective prevention and punishment.
Recently, some feminist researchers and social scientists have argued that sexual desire is not the cause of rape and that rape is not an instinctive human behavior. They expressed concern that concluding rape is instinctive and an evolutionary adaptation could result in providing an excuse for the act of rape. In response, evolutionary biologists including Randy Thornhill counter that rape is an evolutionary adaptation and a natural, instinctive behavior. They emphasize that natural selection does not consider ethical standards, so whether rape is adaptive is separate from questions of morality.
Evolutionary psychologist Cosmides states she does not agree with the claim that rape is simply violence and a socially learned behavior. He views rape as a behavior shaped by natural selection, suggesting males may have utilized it to enhance reproductive success. For a behavior to be considered an adaptation implies it was shaped by natural selection for a specific purpose. Thus, if rape is an adaptation, it exists because it provided reproductive benefits; conversely, if it is not an adaptation, it is merely an accidental byproduct of the reproductive process.
The claim that rape is an adaptation for reproduction and a result of natural selection finds some support in the fact that rape behavior is observed in animals other than humans. Rape occurring within orangutan populations is widely known, and in 2011, a case of interspecies rape was observed in the wild, where a sea otter raped a seal. These cases suggest that rape may not be a socially learned behavior but rather one selected and retained during evolution.
Counterarguments exist. If rape were an adaptation formed by natural selection, it should be a dominant behavior, like a trait appearing in the majority of individuals. The fact that rape is not a dominant behavior suggests it cannot be an adaptation. However, an adaptation does not necessarily need to be widespread across the entire population. Even if a specific behavior appears only in a relatively small number of individuals, natural selection can maintain that behavior if it provides reproductive benefits to those individuals. In response to this counterargument, it could be pointed out that rape is an excessively specialized and rare behavior, and this rarity could be criticized as contradicting the claim that rape is an adaptation.
However, the low incidence of rape is specific to modern society; in early human groups or among certain animals, rape may have been relatively common. The hypothesis that males in primitive societies used rape as a means to pass on their genes also arises in this context. Of course, the actual frequency of rape in early human societies remains unclear, and how often it occurs in animals is also a matter of debate.
Evolutionary biologists counter these questions by pointing to the fact that rape rates surge dramatically in modern, pseudo-primitive situations like war. The fact that rape increases when moral regulation weakens strongly suggests that rape was likely far more frequent in early human societies than it is today. Furthermore, aside from courtship behaviors seen in some mammals and birds, sexual behavior in many animals can take coercive forms, indicating that rape may be a behavior that persists as a result of natural selection.
Another counterargument against the claim that rape is adaptive is that it fails to explain same-sex rape, incestuous rape, and rape of children. Instances where rape occurs unrelated to reproductive purposes lead to the argument that rape cannot be adaptive. However, this can be explained by the evolution of reproductive desire shifting from direct forms to unconscious sexual urges. That is, the reproductive drive of early humans was replaced by the general desire we now call sexual desire. In this process, sexual impulses could arise even toward targets not directly related to reproduction.
This is explained by a principle similar to why humans still prefer high-calorie foods today. During times when hunting was difficult, the need to consume as many calories as possible from a single hunt led to a tendency to prefer high-calorie foods. This tendency persists even in modern times, when it is no longer a survival necessity. Similarly, as the reproductive urge became latent in the form of sexual desire, rape—which is not directly linked to reproduction—also became possible. This provides grounds for the argument that rape is a type of instinctive behavior and cannot be explained solely by socially learned actions.
Cases difficult to explain through adaptation, such as same-sex rape or rape of women outside their fertile period, can be interpreted as phenomena arising during the process of reproductive urges transforming into unconscious sexual desire. In modern society, the motivations for rape are diverse, and factors like sexual desire, anger, and the desire for power are often intertwined. Nevertheless, some evolutionary biologists argue, based on the various cases presented earlier, that rape is a remnant adaptation from the process of natural selection.
However, the fact that rape is a natural phenomenon or contains instinctual elements does not justify or validate it. Scientific discourse must be value-neutral, while ethical judgments belong to a separate academic domain. To summarize the discussion: according to some scholars, rape may be an adaptive behavior formed during evolution, and this scientific conclusion must be understood separately from the moral or legal evaluation of rape.
