In this blog post, we will examine the adaptationist debate surrounding the causes of rape and sexual violence based on Richard Dawkins’ ‘The Selfish Gene’ and the concept of adaptation in evolutionary theory, and explore how current research understands this issue.
Evolutionary biologist Richard Dawkins published ‘The Selfish Gene’ in 1976. One of the key perspectives Dawkins presented in this book is that genes can be viewed as a crucial unit of analysis when understanding natural selection. The bodies of living organisms, including humans, can be described as a kind of vehicle formed through the process by which genes survive and are transmitted across generations, and natural selection ultimately acts to ensure that genes that increase their own replicative potential are passed on to the next generation in greater numbers. However, the term “selfish” here does not imply that genes possess consciousness, desires, or the capacity for moral judgment. Nor does it mean that all human behavior is directly determined by genes. Dawkins’ argument should be understood as an evolutionary perspective intended to explain how genes are maintained and spread through the process of natural selection.
Following the publication of ‘The Selfish Gene’, this perspective sparked significant debate among both the academic community and the general public. In particular, diverse opinions were raised regarding whether even complex human behaviors could be explained by natural selection at the genetic level. Humans engage in various biologically grounded behaviors, such as seeking food when hungry, sleeping when tired, and forming sexual desires and attachments. However, it is not straightforward to clearly distinguish, among the countless behaviors humans exhibit, which aspects are related to evolutionarily formed tendencies and which are shaped by learning during development, culture, and the social environment. Today, even within behavioral science and evolutionary biology, it is generally accepted that human behavior should be understood as a complex phenomenon in which biological traits, developmental processes, individual experiences, social relationships, and cultural environments mutually influence one another, rather than being explained by either genetics or environment alone.
A highly controversial topic related to this is also addressed in ‘Darwin’s Table’. In ‘The Natural History of Rape’, Randy Sonhill and Craig Palmer analyze human rape and sexual coercion from an evolutionary perspective, examining the possibility that rape evolved as an independent adaptation and the possibility that it is a byproduct of other evolutionary psychological mechanisms. Although their discussion is commonly known as the “rape adaptation hypothesis,” the authors themselves did not claim to be able to definitively determine whether rape is an independent adaptation or a byproduct of other adaptations. Since then, this hypothesis has been the subject of prolonged criticism and scrutiny within the academic community. A synthesis of research to date indicates that there is insufficient direct empirical evidence to substantiate the view that human rape is an independent adaptation that evolved specifically for reproduction; indeed, even in recent evolutionary psychology research, some hypotheses proposed in the past—such as the so-called “rape hypothesis due to mate scarcity”—are discussed as examples that have failed to pass empirical verification. Therefore, categorizing rape as an independent instinct shaped by natural selection is inconsistent with the current state of research.
To understand this discussion, it is first necessary to clarify the meaning of “adaptation” as used in evolutionary biology. The fact that a trait is important for survival or that a behavior brings benefits in a specific situation does not automatically mean it is an evolutionary adaptation. Generally, for something to be called an evolutionary adaptation, there must be evidence that a heritable trait or psychological mechanism provided a sustained advantage for survival or reproductive success in a specific past environment and was therefore shaped or maintained through natural selection. Therefore, the mere fact that a behavior exists today or that it may confer a specific benefit to some individuals is not sufficient grounds to judge that the behavior itself is an adaptation designed by natural selection. Behavior may be a byproduct of other adaptive traits, may arise from the influence of learning or cultural environments, or may be the result of multiple factors acting in concert.
In past debates on adaptationism, it was argued that human rape and sexual coercion could also be analyzed from an evolutionary perspective. The fact that such research is conducted does not imply that rape is morally justified. This is because we must distinguish between the scientific study of the causes behind a behavior and the moral judgment of whether that behavior is right. The purpose of studying the biological and psychological background of human behavior is not to condone it, but to understand the conditions under which it occurs and to gain knowledge for more effective prevention. In particular, for behaviors that cause severe harm—such as sexual violence—it is crucial to adopt an approach that examines not only biological factors but also an individual’s experiences, relationships, social norms, power dynamics, culture, and environment. Current public health research also explains sexual violence not as a phenomenon arising from a single cause, but as a complex phenomenon resulting from the interaction of various risk factors at the levels of the individual, relationships, the community, and social structures.
Caution is also required when applying Dawkins’ concept of “the selfish gene” to this debate. Natural selection is not governed by the moral standards of human society; rather, the outcome of natural selection is determined by which genetic traits are passed on more frequently to the next generation. However, this should not be interpreted to mean that genes set specific goals or command humans to act in certain ways. This is because genes are not intentional agents. Therefore, while the expression “genes use rape as a means to be passed on” may be used as a metaphor for the evolutionary process, it should not be accepted as a statement that directly explains scientific causality. The key issue to examine in evolutionary hypotheses is what relationship specific psychological dispositions or behavioral tendencies had with reproductive success in the past, and whether there is actual evidence that the mechanisms shaping such dispositions were maintained through natural selection.
Some past adaptationist explanations have proposed the hypothesis that coercive sexual behavior may have provided reproductive opportunities for males who had difficulty securing voluntary mating partners. However, this line of reasoning alone is insufficient to conclude that rape was an independent evolutionary adaptation. This is because the fact that a person who engaged in a certain behavior happened to reproduce successfully is a completely different matter from the claim that the behavior itself was an adaptation selected by natural selection for reproduction. To argue that a specific behavior was an evolutionary adaptation, one must verify whether a specific psychological mechanism underlies that behavior, whether that mechanism actually increased reproductive success in past environments, and whether the hypothesis in question explains the observed phenomena better than other explanations. To date, no conclusive evidence has been found to support the existence of a distinct psychological adaptive mechanism specific to human rape. On the contrary, some studies suggest that a combination of various factors—such as sexual desire, aggression, impulsivity, a desire for dominance, hostile attitudes toward women, a sense of sexual entitlement, and norms that condone violence—can increase the risk of sexual violence.
How, then, should we view the long-held claim that humans engage in sexual behavior to pass on their genes, and that rape is a form of such behavior? It is precisely at this point that significant counterarguments to the adaptation hypothesis have emerged. The fact that sexual violence occurs even in situations not directly linked to reproduction calls into question the simplistic explanation that rape is a specialized behavior that evolved solely for the purpose of pregnancy or reproduction. Sexual violence against children and the elderly, same-sex sexual violence, and sexual violence in situations where pregnancy is impossible all demonstrate that rape cannot be explained solely as a reproductive behavior. Of course, these examples alone do not automatically invalidate all evolutionary explanations, but they clearly show that it is difficult to explain all instances of human sexual violence with the simple hypothesis that “rape is an instinct developed for reproduction.”
In past debates, the fact that rape occurs even against women who are not in their fertile period or victims who cannot become pregnant was presented as one of the arguments refuting the adaptation hypothesis. In response, some evolutionary explanations countered that, since humans cannot perfectly judge a partner’s fertility, there was no need for sexual desire to evolve to function strictly only during the fertile period. In other words, there is no perfect one-to-one correspondence between sexual desire and reproductive capacity. While this counterargument has a certain evolutionary logic to it, the existence of sexual violence outside the fertile period does not necessarily support the rape-as-adaptation hypothesis. This is because the fact that a phenomenon does not contradict a specific hypothesis is distinct from the hypothesis actually being proven. In particular, the existence of various forms of sexual violence—such as sexual violence against children and same-sex sexual violence—that are difficult to link directly to reproduction demonstrates the need for a much broader analysis of the causes of sexual violence.
Furthermore, defining rape as stemming solely from either sexual or violent motives is an overly simplistic approach. In the past, there was a heated debate over whether rape primarily stemmed from sexual desire or from power, domination, and aggression. However, current research does not view these factors as necessarily mutually exclusive. The risk of committing sexual violence is associated with various factors, including aggression and impulsivity, attitudes that justify violence, hostility toward women, a sense of sexual entitlement, harmful use of alcohol and drugs, associations with violent peer groups, experiences of violence during one’s upbringing, and social norms that tolerate gender inequality and violence. Therefore, assuming a situation where the victim does not resist, it is impossible to determine whether rape is a sexual act or a violent act based solely on whether the perpetrator uses physical violence. The essence of rape and sexual violence lies not simply in whether physical violence was used, but in the fact that sexual acts are carried out coercively and under duress without the other party’s free consent. The World Health Organization also defines sexual violence as an act that infringes upon a person’s sexual self-determination through various forms of coercion—including not only physical force but also threats and psychological pressure.
However, this does not mean that moral judgments should be directly applied to the process of scientifically analyzing the causes of rape. There must be a clear distinction between explaining why a phenomenon occurs and evaluating that phenomenon as morally right or wrong. Even if it is revealed that a certain behavior in the natural world has evolved, this fact cannot serve as a basis for morally justifying that behavior. Conversely, the fact that a behavior is morally reprehensible does not mean we should refrain from studying its biological and psychological causes. This distinction is particularly important in the study of human behavior from an evolutionary perspective. However, we must also be wary of treating unverified hypotheses as facts under the guise of seeking scientific explanations.
Looking at the debate to date, it is important to note that there is insufficient evidence to conclude that rape is a distinct adaptation that evolved specifically in humans. While it has been suggested that, in the past, men who had difficulty securing voluntary mating opportunities may have gained reproductive opportunities through coercive sexual behavior, this possibility alone is insufficient to conclude that rape was an essential reproductive strategy shaped by natural selection. Even in recent evolutionary psychology, there are discussions of cases where hypotheses—such as the so-called “mate scarcity hypothesis”—that attempt to explain rape as an adaptation to specific reproductive problems have been refuted through empirical testing. Meanwhile, research continues to examine the possibility that rape is not so much a specific, independent adaptation as it is a byproduct arising from the combination of other psychological traits—such as sexual desire, aggression, and opportunistic behavior—with specific social and environmental conditions. However, these explanations should not be used to reduce all forms of human sexual violence to a single cause.
Ultimately, to understand the underlying mechanisms of rape and sexual violence, it is problematic to make judgments based solely on two opposing choices, such as “instinct or culture,” “sexual desire or violence,” or “nature or nurture.” Human behavior develops based on biological tendencies shaped by evolutionary history, but at the same time, it is constantly influenced by an individual’s experiences and learning, family and peer relationships, cultural norms, perceptions of gender roles, and power dynamics and social institutions. Current public health research also views sexual violence not as stemming from a single biological or cultural cause, but as a phenomenon resulting from the interaction of various risk factors present in individuals, relationships, communities, and social structures. What is needed to understand the mechanisms behind sexual violence is not to accept any single theory as the absolute answer, but rather an attitude that examines how well each hypothesis is supported by empirical evidence.
This is also the crucial question raised by ‘The Selfish Gene’. Acknowledging that humans are products of evolution does not mean we must accept that all human behavior is determined by genes. Humans possess the ability to recognize and learn from their impulses, create social rules, and control their behavior. Even if a behavioral tendency has an evolutionary background, this does not make that behavior inevitable for an individual. Furthermore, the fact that certain traits exist as a result of natural selection does not imply that human society must tolerate them. This is because what exists in nature and what is desirable in human society are two distinct matters.
Therefore, when understanding the act of rape, we must be most wary of two types of oversimplification. One is explaining rape solely as an innate instinct or reproductive strategy; the other is ruling out the possibility of biological factors from the outset and asserting that it is solely the result of culture and learning. The role of science is not to choose which explanation aligns more comfortably with our moral intuitions, but to test various hypotheses based on evidence. At the same time, society’s role is to use the knowledge thus accumulated to prevent sexual violence, protect victims, and gradually reduce the environments and norms that foster violence. Sexual violence is an act that seriously infringes upon the physical and mental health and human rights of victims, and the purpose of researching its causes should not be to justify such violence but to understand it more accurately and prevent it.
The difficulty of clearly distinguishing between what aspects of human behavior are products of evolution and what are the results of learning and culture will remain a challenge for the foreseeable future. However, rather than viewing genetics and culture as mutually exclusive explanations, we now need to understand human behavior as a process in which biological predispositions, development, learning, and the social environment influence one another. Rape and sexual violence are also not phenomena that can be explained simply as the commands of the “selfish gene” or a single reproductive instinct. While evolutionary theory can serve as an important tool for exploring the origins of human behavior, a hypothesis does not become fact simply because it is evolutionary in nature. Scientific explanations require verifiable evidence, and the question of what social or moral conclusions to draw from those explanations must be addressed as a separate issue. By maintaining this distinction, we can gain a more accurate understanding of uncomfortable and complex human behavior without turning a blind eye to it, and without confusing scientific facts with moral judgments.
