In this blog post, we’ll examine how rape can be explained from the perspectives of evolutionary psychology and behavioral ecology, as well as the various arguments and counterarguments regarding whether rape can be viewed as an adaptation.
Is rape an adaptation? It’s certainly a topic that’s difficult to discuss openly in everyday life. “Darwin’s Table” addresses this sensitive topic. Proponents primarily cite ‘A Natural History of Rape: Biological Bases of Sexual Coercion’ (2000), co-authored by behavioral ecologist Randy Thornhill, to argue that rape is an evolutionary adaptation. They argue that rape served to increase reproductive opportunities for some men who struggled to find mates, and that this behavior was maintained through natural selection over the course of evolution.
On the other hand, opponents argue that the evidence presented in ‘A Natural History of Rape’ is insufficient, and that if rape were an adaptation, it would be difficult to explain cases such as same-sex rape, incest, and child sexual abuse. They also point out that the logic presented in the book alone has limitations in explaining the complex social and cultural behaviors of humans. While introducing the pro-argument, the author uses the example of obesity to illustrate that a phenomenon that was adaptive in the past may no longer be adaptive today.
Before refuting the pro-rape argument, I will set aside the ethical issues surrounding rape for the purposes of this discussion. Here, I simply wish to consider whether the proposition “rape is an adaptation” is scientifically valid. I argue that rape is a byproduct of sexual desire rather than an adaptation, based on the following two reasons.
First, if rape is the result of adaptation, the purpose claimed by the pro-rape side—namely, “the function of increasing reproductive success”—must be actually proven. However, it has not been clearly proven that rape actually increases reproductive success. In modern society, there are cases where rape victims opt for emergency contraception or choose to terminate a pregnancy within the limits permitted by national laws. Therefore, while it is difficult to judge whether rape is an evolutionary adaptation based solely on today’s reality, it is at least unreasonable to conclude that rape directly leads to reproductive success.
Furthermore, cases of sexual violence include victims who are children and therefore incapable of reproduction. In such cases, the goal of reproduction itself does not apply. If rape is an adaptation for reproduction, how can these cases be explained? Similarly, sexual violence committed by men against other men or incestuous sexual violence is also difficult to explain solely in terms of reproduction.
In response, proponents might argue that sexual violence against men, incestuous sexual violence, and sexual violence against children are exceptional phenomena or byproducts that arose during the adaptive process. However, whether it is truly valid to explain all these diverse cases solely as exceptional mutations or byproducts remains a subject of debate. This is because the scope of phenomena that need to be explained is too broad to be dismissed simply as exceptions.
Second, in ‘A Natural History of Rape: Biological Bases of Sexual Coercion’, which proponents cite as evidence, male scorpionflies are presented as a case study to examine whether rape is an adaptation. Male scorpionflies possess a physical structure that enables forced copulation, and based on this, the authors argue that rape behavior in human males could also be an adaptation.
However, scorpionflies are insects belonging to the phylum Arthropoda and are evolutionarily very distant from humans, who are primates. Consequently, critics have pointed out that there are limitations to using such examples to directly explain human behavior. In fact, various criticisms regarding the research methods and interpretations of these studies have been raised, and the debate continues even within the field of evolutionary psychology.
Of course, there are numerous reported cases of forced copulation in the animal kingdom. Based on this, one could argue that similar behavior may have emerged in humans during the course of evolution. However, there is still a lack of clear evidence regarding exactly how such behavior contributed to reproductive success. If rape is indeed an adaptation, a specific mechanism must be proposed to explain how it increased reproductive success compared to normal mating.
The question of whether “rape is an adaptation or not” is a highly complex issue. This is because, even when considering only scientific explanations and setting aside ethical judgments, both sides present arguments that are persuasive to a certain extent. Proponents argue that rape is an adaptation, citing the fact that rape has existed for a long time. On the other hand, opponents argue that rape is not an adaptation but rather a byproduct of sexual desire or other psychological mechanisms—or a behavior resulting from a combination of sociocultural factors—citing examples such as rape-murder, same-sex sexual violence, incestuous sexual violence, and child sexual abuse.
There are significant challenges in explaining diverse cases—such as rape-murder, same-sex sexual violence, incestuous sexual violence, and child sexual abuse—as mere exceptions arising from the process of adaptation. Whether these phenomena can be sufficiently explained by the single concept of “adaptation” remains an area requiring ongoing research.
Rape is a topic that is difficult to discuss openly and an issue that is not easy to contemplate deeply. Attempts to explain it from the perspective of evolution and natural selection may offer one possible avenue for understanding human behavior. However, based on research to date, it is difficult to conclude that sufficient evidence has been accumulated to accept this as an established theory. Even setting aside ethical concerns, a more cautious approach would be to understand the complex behavior of rape as a phenomenon shaped not only by biological factors but also by psychological, social, and cultural factors acting in concert.
