In this blog post, we’ll examine the meaning of “adaptation” in biology and discuss whether rape can be viewed as an adaptation, focusing on the evolutionary biological debate over whether rape is an adaptation.
In everyday life, almost no one reacts positively when they hear the word “rape.” This reflects the fact that in modern society, rape is both a criminal act and a behavior strongly prohibited by society. However, ‘Darwin’s Table’ presents a hypothetical debate among renowned biologists on the topic, “Is rape an adaptation?” While it may seem questionable how rape—generally perceived as a negative act—could be viewed as an adaptation, this book discusses whether rape is an adaptation from a biological perspective, rather than a cultural one.
To determine whether rape is an adaptation, we must first accurately understand the meaning of “adaptation” as defined in biology. The term “adaptation” as we commonly use it—as in “I’ve adjusted to the time difference” or “I’ve adapted to the company culture”—refers to an individual changing their state to fit a given environment. However, the meaning of adaptation in biology is different.
For example, let’s assume that two types of finches—Type A and Type B—with different beak shapes coexisted on the Galápagos Islands. After some time, observations revealed that only finches with Type A beaks remained on the coast, while only those with Type B beaks inhabited the foothills. This phenomenon occurred due to natural selection based on the habitat. This is because individuals with beaks that provided a survival advantage in each respective environment survived and successfully reproduced. In such cases, biology describes the finches with Type A beaks as having adapted to the coastal environment. In other words, “adaptation” in biology refers not to changes in individual organisms, but to traits formed through natural selection at the population level.
Not every result of natural selection can be immediately termed an adaptation. Since the criteria and methods for determining what constitutes an adaptation are not clear-cut, scholars may hold differing views. Even regarding the same phenomenon, some scholars argue that it is an adaptation because it is the direct result of natural selection, while others interpret it as a byproduct of another, pre-existing adaptation. In other words, the same phenomenon can be viewed either as an adaptation or as a byproduct.
The position that interprets a phenomenon as an adaptation is called adaptationism, while the opposing position is called anti-adaptationism. These two schools of thought have long debated whether human psychology and behavior evolved through natural selection, and a prime example of this is the debate over whether “rape is an adaptation.”
To discuss whether rape is an adaptation, “Darwin’s Table” divides scholars into two camps for a debate. The adaptationist camp includes evolutionary psychologist Cosmedis and linguist Pinker, while the anti-adaptationist camp includes evolutionary geneticist Coine and paleontologist Gould. Both sides refute each other’s arguments and present their own positions.
Adaptationists argue that rape is also a form of adaptation selected by natural selection during the evolutionary process. In other words, they view rape as an adaptation that evolved to increase men’s reproductive success, seeing it as a behavior related to reproduction rather than mere violence. On the other hand, anti-adaptationists argue that rape is a byproduct of excessive sexual desire or other psychological traits and is, at its core, a violent act. They also counter that it is difficult to view rape as an adaptation based solely on the evidence presented by the adaptationists.
I believe it is difficult to view rape as an adaptation based solely on the logic presented by adaptationists. Even an examination of ‘The Selfish Gene’, written by Dawkins—a leading scholar in the adaptationist camp—suggests that rape is not an adaptation.
Dawkins explains that if a dominance hierarchy exists within a group, the psychological mechanisms governing that hierarchy are shaped by genes.
In other words, an adaptation refers to the manifestation of psychological mechanisms programmed by genes. However, he also explains that the outcome resulting from the interaction of adaptations at the group level should not itself be regarded as an adaptation. To put it another way, while the psychological mechanisms that form a dominance hierarchy are an example of an adaptation shaped by genes, the phenomenon of a group actually adopting a specific dominance hierarchy is merely the result of the interaction of multiple adaptations—it is not an adaptation in and of itself.
This logic can also be applied to rape. The psychological mechanisms related to rape can be viewed as manifestations of psychological mechanisms associated with human sexual desire, and sexual desire itself, as an instinctive human trait, could be interpreted as an adaptation. However, the act of rape itself—which we are discussing—is an outcome arising from the interaction of various individuals and environmental factors, and it is difficult to conclusively assert that it is a single adaptation directly selected by genes. In other words, Dawkins himself distinguishes between psychological mechanisms and actual behavior in his book when determining whether something is an adaptation, and from this perspective, it is difficult to view the act of rape itself as an adaptation.
Adaptationists would likely disagree with this argument. They would likely argue that rape is a behavior that occurs at the individual level, not the group level. In fact, rape is an act performed by individuals, not groups, and is a behavior chosen by males who have difficulty securing reproductive opportunities in order to pass on their genes to future generations. In other words, the position is that rape should be understood as a reproductive strategy chosen by males who are at a disadvantage in the competition for survival.
However, viewing rape as a phenomenon that occurs only at the individual level does not align with the definition of adaptation discussed earlier. As explained earlier, an adaptation refers to a trait that emerges as a result of natural selection at the population level. Even if a particular individual succeeds in reproducing through rape, it is difficult to conclude from that single instance alone that the act of rape itself is a product of natural selection. Natural selection refers to the process by which a specific trait, demonstrating relatively higher survival and reproductive success in competition with other traits, is passed on to future generations.
If rape were an adaptation, a population in which reproduction occurs through rape as well as through normal means would have to demonstrate higher reproductive success over the long term compared to a population in which reproduction occurs only through normal means. However, it is difficult to prove such a comparative advantage based solely on instances of rape involving a few individuals who are at a disadvantage in the competition for survival. Therefore, while the act of rape can be understood as the result of various interactions occurring at the population level, it is difficult to view it as an adaptation—that is, a direct product of natural selection—in and of itself.
Adaptationists would counter this by arguing that natural selection is a process that selects traits of individuals, not populations. They contend that when multiple individuals possess different traits and environmental changes cause only those with a specific trait to survive and pass on their genes to future generations, that trait should be considered to have been selected by natural selection.
For example, suppose there is a carnivorous individual A and a non-carnivorous individual B. Adaptationists argue that if, over time, individual A survives while individual B disappears, this can be interpreted as the carnivorous trait having been selected by natural selection.
However, what matters in natural selection is not the survival of a single individual. Individuals within a population share similar traits, and natural selection is determined by the extent to which these traits are maintained and altered within the population. In other words, what matters is not whether a specific individual survived, but rather how well a specific trait has adapted within the population as a whole.
For example, suppose carnivorous individuals made up 50% of the population. If a major change in the natural environment subsequently caused the total population to decline, but the proportion of carnivorous individuals among the survivors increased to 80%, we can interpret this to mean that the trait of carnivory was subject to natural selection in the new environment. Conversely, if that proportion remained virtually unchanged, we can conclude that the trait was not significantly affected by the environmental change; if it had declined sharply, we could judge it to be a trait that was at a disadvantage in natural selection.
A common error made when arguing that rape is an adaptation from a biological perspective is viewing the act of rape in isolation, without sufficiently considering the various other conditions and environmental factors. This involves understanding rape solely as behavior at the individual level and interpreting it as having been subject to natural selection based solely on the fact that some individuals succeeded in reproducing through rape.
However, in biology, when studying the human body, we do not analyze a single organ in isolation. We also consider how that organ relates to and interacts with other organs. Similarly, a single behavior must be understood within the context of its interactions with the surrounding environment and the group. This is because even the same behavior can yield vastly different outcomes depending on environmental and social conditions.
Therefore, when viewing rape from a biological perspective, it should be understood as a phenomenon emerging from various interactions within a group, rather than interpreted simply as the behavior of a single individual. Furthermore, if we adopt the view that the outcome resulting from the interaction of multiple adaptations at the group level cannot itself be considered an adaptation, it is difficult to conclude that the act of rape itself constitutes an adaptation.
