In this blog post, based on the debate between adaptationism and anti-adaptationism in evolutionary biology, we will examine and critically review the argument that rape is an adaptation shaped by natural selection.
Darwin’s Theory of Evolution and the Adaptationism Debate
In 1859, Charles Darwin published ‘On the Origin of Species’. In this book, Darwin explained the process by which organisms adapt and evolve through the mechanism of “natural selection.” The book had an impact on human thought and culture that is difficult to put into words, and some have even assessed that Darwin “changed the way we understand ourselves on this planet.” Darwin’s argument is as follows: Mutations can occur in the genes that determine an organism’s traits; if a new trait resulting from a mutation aids survival and reproduction and is passed on to the next generation, that trait is preserved by natural selection. The products of natural selection that survive in this way are called “adaptations,” and organisms evolve through the accumulation of these adaptations over long periods of time.
Today, there are almost no biologists who deny the very concept of biological adaptation through natural selection. However, there are still diverse views regarding the scope and influence that natural selection can explain. “Adaptationists” view the power of natural selection as very strong and explain various phenomena as the result of adaptation. On the other hand, “anti-adaptationists” argue that natural selection alone cannot explain all phenomena and criticize adaptationism for interpreting many phenomena as adaptations. The two sides hold differing views on various traits, including human language ability, and one of the most prominent debates is the question: “Is rape an adaptation?”
In ‘Darwin’s Table’, Jang Dae-ik presents the arguments of adaptionists and anti-adaptionists regarding rape. Adaptionists suggest that rape may have been one of the adaptive behaviors that increased men’s reproductive success. They also emphasize that this argument is not intended to ethically justify rape but is merely a hypothesis based on facts, and that rape is clearly a wrongful crime that must be punished. On the other hand, anti-adaptationists counter that the evidence presented by adaptationists—such as the age distribution of rape victims—does not sufficiently support their claim, and they criticize the assertion that “rape is an adaptation that increases reproductive success.”
The most important core concepts in Darwin’s theory of evolution and evolutionary biology are “natural selection” and “adaptation.” Adaptation through natural selection is the process by which traits that aid survival and reproduction become established in a population over a long period of time, and it is regarded as the key mechanism driving evolution. To determine whether a trait is an adaptation, one must first ask, “Can that trait be subject to natural selection?”—that is, “Do individuals possessing that trait have a survival and reproductive advantage over those who do not?” If a trait is an adaptation, it must at least confer an advantage for survival and reproduction. Based on this point, I will argue that even if a genetic predisposition related to rape behavior were to exist, it could not be subject to natural selection.
In biology, the concept of “fitness” is used to assess the likelihood that a trait will be subject to natural selection. Fitness is a concept that indicates how many genes an individual with a specific genetic trait passes on to the next generation; it is a key indicator of natural selection in the evolutionary process. Traits with high fitness increase in frequency over generations, while those with low fitness gradually decline. Therefore, assuming there is a trait associated with rape behavior, we need to examine whether it is actually advantageous for humans in terms of survival and reproduction, and how its fitness is manifested.
Can Rape Be an Adaptation in Human Society?
If asked whether rape is advantageous for human survival and reproduction, most people would answer “no.” Humans have formed cooperative societies based on their exceptional communication skills and have developed laws and norms to maintain them. Therefore, since rape is a socially prohibited crime that is subject to punishment, it is difficult to view it as behavior that is advantageous for survival and reproduction. However, adaptationists argue that since laws and institutions in human society emerged very recently on the evolutionary timescale, we should not use them as a basis for determining whether something is an evolutionary adaptation. If so, was rape truly free from any social sanctions throughout human evolutionary history? To answer this question, we must also consider the characteristics of the human species.
Compared to other animals, humans—who are relatively physically weak—had no choice but to live in groups. In fact, many studies generally agree that human ancestors have lived in groups for a very long time. Furthermore, to maintain group life, various rules would have been established based on agreements among members, whether explicit or implicit. Such rules are not unique to humans but are commonly observed in animals that live in groups as well. In particular, it is highly likely that humans developed various social norms to maintain stable communities based on their exceptional communication abilities. Of course, it is difficult to determine exactly what those rules were like today.
However, the legal codes left behind after humanity began using writing provide important clues for understanding past societies. Since the pace of civilizational development was very slow at that time, it is likely that a lifestyle considerably more primitive than today’s was largely maintained. Furthermore, social norms and customs tend to accumulate and be passed down through generations. Both the Code of Hammurabi and the Hittite Code—among the oldest legal codes in human history—contain provisions regarding rape. This can be seen as evidence that the need to regulate rape has existed for a very long time. Taking these records into account, it is highly likely that human societies have long viewed rape negatively and imposed sanctions on it to maintain communal order.
For humans, who do not possess exceptional physical abilities, cooperation within the community is a crucial factor for survival. Therefore, individuals subject to severe social sanctions from the community are likely to be at a disadvantage in terms of both survival and reproduction. Furthermore, the probability of pregnancy resulting from a single sexual encounter is low, and even if pregnancy does occur, it is difficult to generalize or assume that the victim will choose to give birth and raise the child. Furthermore, studies have reported that sexual violence can have serious physical and psychological effects on the victim, and these effects can lead to negative outcomes during pregnancy and childbirth. Considering these points, even if we assume that traits associated with rape exist, it is difficult to view them as having high fitness. Therefore, it is highly unlikely that such traits would become widespread through natural selection.
Evolutionarily Stable Strategies and the Adaptive Potential of Rape
Another concept that supports this is the “Evolutionarily Stable Strategy (ESS).” This is a concept that integrates game theory into behavioral ecology, referring to a state in which, when most individuals employ a specific strategy, no other strategy can infiltrate and spread within the population. An evolutionarily stable strategy is not easily replaced by other strategies if certain conditions are met.
Let’s assume that strategy S is the “no-rape strategy” and strategy T is the “rape strategy.” As we have seen, human society is sustained through cooperation, and if a community has consistently viewed rape negatively and imposed sanctions against it, the “rape strategy” would find it difficult to spread within that community. From this perspective, it is reasonable to interpret that the rape strategy is unlikely to become an evolutionarily stable strategy in human society.
If humans were a species that did not live in groups, there might be room to consider the possibility—as advocated by adaptationists—that rape behavior could have aided reproduction in certain situations. However, humans are a species that has inherently survived through communal living and cooperation, and the norms necessary to maintain the community have evolved alongside these traits. Considering this, we can conclude negatively to the question, “Do individuals who commit rape have a survival and reproductive advantage over those who do not?”
Thus far, we have critically examined whether rape is indeed a trait advantageous for survival and reproduction, and we have analyzed the adaptationist claim that “rape is an adaptation” based on fitness and evolutionarily stable strategies. Summarizing this discussion, even setting aside ethical issues, it is difficult to conclusively assert that the act of rape is an adaptation selected by natural selection based on survival and reproductive advantages. Therefore, claims that view rape as the result of adaptation require thorough examination and careful interpretation.
