In this blog post, I will examine the arguments and evidence regarding whether rape is the result of an adaptation from an evolutionary perspective, and summarize my own views on the matter.
Today, many scholars regard Darwin as a “genius.” His theory of evolution has had a profound impact not only on biology but also on human society as a whole, and it is recognized as a theory that transcended the limitations of its time. One of the core concepts in evolutionary theory is “adaptation.” Darwin explained that through natural selection, organisms have evolved in ways that make it easier for them to adapt to their environment. Based on this theory, some evolutionary psychologists have proposed the hypothesis that male rape behavior may also be the result of an evolutionary adaptation. They argue that some males who failed to secure mating opportunities may have engaged in such behavior as part of the process of natural selection to increase their reproductive success. As primary evidence, they cite studies analyzing the age distribution of female rape victims and cases of forced copulation observed in certain animals. In particular, evolutionary biologist Randy Thornhill proposed the hypothesis that rape could be a reproductive adaptation, citing evidence such as the proportion of female victims of childbearing age, and also mentioned cases where morphological characteristics related to forced copulation have been discovered in certain insects.
I, too, believe this hypothesis is persuasive to a certain extent. However, I would like to clarify from the outset that the question of whether it is an adaptation and the issue of ethical responsibility are entirely separate matters. Discussions regarding adaptation are conducted strictly from a biological perspective; even if a specific behavior were to have emerged through the evolutionary process, rape remains a crime that inflicts severe harm on others and is an act that can never be justified. Natural selection is not a process of making ethical judgments but merely a process through which traits that influence survival and reproduction are passed down across generations.
The main reason I believe rape may be an adaptation is that some studies suggest that situations involving forced sexual intercourse in humans may be accompanied by certain physiological changes related to reproductive potential. However, these research findings remain highly controversial within the academic community, and no consistent conclusion has been reached to date. While some studies have analyzed the likelihood of conception or specific physiological responses in situations of sexual violence, there is not yet sufficient scientific consensus to conclusively assert that rape is an evolutionary adaptation. Nevertheless, it is true that there are studies that hypothetically examine the possibility that forced sexual acts may have provided reproductive opportunities in certain environments. In this regard, I believe it is necessary to consider the possibility that this behavior may have been subject to a certain degree of selective pressure during the process of natural selection.
Those who argue that rape is not a form of adaptation contend that it is inappropriate to generalize examples from other species to humans, and that men who commit rape are ostracized by society and therefore unlikely to be subject to natural selection. I will now offer a logical rebuttal to this argument.
First, I believe the claim that comparisons with other organisms are unreasonable is an interpretation that fails to fully consider the basic premises of evolutionary theory. Evolutionary theory rejects the view that humans are fundamentally distinct from other animals and is based on the premise that all living organisms have diverged from a common ancestor. Darwin used the metaphor of a tree with branching limbs to illustrate this. Humans are also just one of countless species and have acquired various traits in the process of adapting to their environment. Therefore, research that infers human traits by referencing those of other animals is a method commonly used in evolutionary biology. In fact, forced mating behavior has been observed in various animals, and morphological or behavioral characteristics associated with this behavior have been studied in some species. Of course, this alone does not allow us to conclusively assert that the same mechanism exists in humans, but I believe it serves as a meaningful starting point for research.
Furthermore, as mentioned earlier, given that there are studies analyzing the relationship between rape and reproductive potential in humans, the criticism that this research relies solely on examples from other animals is difficult to consider a sufficient rebuttal.
Second, adaptation is a trait formed through repeated natural selection over a very long period of time. The history of society organized around norms and laws is a very short period compared to the entire history of human evolution. Therefore, it is difficult to assume that an evolutionary trait that has already been established would disappear in a short period of time simply because social sanctions exist.
A prime example illustrating this is obesity. Humans have long lived as hunter-gatherers in environments where food shortages could occur at any time. In such environments, the ability to efficiently store fat in the body likely provided a survival advantage. However, even though food is readily available in modern society, this trait persists, and it is sometimes cited as one of the causes of rising obesity rates. In other words, while the environment has changed rapidly, evolutionary traits change relatively slowly. Considering this, I believe it is difficult to conclude that rape is unrelated to natural selection based solely on the fact that perpetrators have been punished since the formation of society.
We have examined the evidence suggesting that rape may have emerged as an adaptive trait over a long period of time. Now, we also need to examine the argument regarding whether “rape actually increases the probability of offspring reproduction”—the most important condition for natural selection to occur. In fact, researchers who argue that rape is not an adaptation present the following counterarguments: not all rape victims are women of childbearing age; same-sex rape exists; and even if a female victim becomes pregnant, the physical and psychological trauma makes it unlikely that she will carry the pregnancy to term. Actual surveys have also reported that the proportion of women of childbearing age among rape victims is not 100%.
Regarding these counterarguments, I hold the following view. I believe that cases such as same-sex rape or child rape are likely byproducts arising from the manifestation of strong sexual desire, rather than the act of rape itself. If the act of rape was subject to natural selection in specific historical environments to increase reproductive success, the desire formed during that process could manifest in forms different from its original function.
Of course, this explanation is merely a hypothesis and is not a conclusion established by the academic community at present. In fact, the causes of homosexuality, sexual orientation, and sex crimes are being studied across various fields—including biology, psychology, sociology, and neuroscience—and it is difficult to explain them based on any single theory. Therefore, it is difficult to conclude that there is sufficient evidence to simply label same-sex rape or child rape as byproducts of sexual desire.
Furthermore, I believe that men are directly involved in the reproductive process only up to the point of fertilization. The various factors that arise during pregnancy and childbirth may be subject to separate selective pressures. Therefore, I believe we must be cautious about concluding that rape is not an evolutionary adaptation based solely on the outcomes following pregnancy.
Critics of adaptationism argue that proponents of adaptationism are caught up in excessive adaptationism. Before addressing this, I would like to point out that adaptationists do not claim that every trait is unconditionally an adaptation; rather, they reach conclusions only after reviewing whether a trait is an adaptation by synthesizing various lines of evidence. When adaptation occurs through natural selection, the genetic traits of a population ultimately change. However, since it is difficult to verify this process directly, researchers collect indirect evidence through behavioral and physiological characteristics, as well as comparative studies between animals and humans.
In fact, behaviors and morphological characteristics related to forced copulation have been reported in some animals, and since humans share an evolutionary continuum with other animals, research in this area is also being conducted. Furthermore, some studies have attempted to analyze the relationship between forced sexual acts and reproductive success, and based on a synthesis of these findings, some researchers have raised the possibility that rape could be an adaptation. On the other hand, there are numerous counterarguments stating that this evidence alone is insufficient to conclusively label rape as an adaptation and that social and cultural factors must also be taken into account. Therefore, rather than viewing one side as having been fully proven at this point, it is more appropriate to understand this as a research topic that continues to be verified based on diverse evidence.
Thus far, I have examined the argument that rape may be part of an adaptation, the evidence supporting it, and the counterarguments against it. Darwin’s theory of evolution provides a crucial theoretical framework for understanding the process through which humanity has evolved into its present form. However, the fact that evolutionary theory can explain the origin of a certain behavior does not mean it can explain the morality or legitimacy of that behavior. Exploring the possibility that a specific behavior has an evolutionary origin and evaluating that behavior ethically are issues on different planes. Therefore, I believe it is necessary to discuss the issue of rape by clearly distinguishing between biological perspectives and ethical and legal perspectives, and that it is important to continue deepening our understanding through various studies and critical reviews in the future.
