In this blog post, I will examine the debate over whether rape is an adaptation or a byproduct of adaptation, and reflect on the issue primarily from my own perspective.
Dictionary definitions define rape as a crime in which sexual intercourse is forced upon another person without their consent through illegal means such as assault or intimidation. In the past, the view that rape was merely an act of violence and a socially learned cultural behavior was widely accepted. However, after Randy Thornhill of the University of New Mexico and Craig Palmer of the University of Colorado argued in ‘A Natural History of Rape’ that rape is also an adaptation, a perspective emerged that seeks to understand rape as an evolutionary adaptation. They sought to view rape as an adaptation and approach it scientifically. While the attempt to scientifically understand social phenomena is meaningful in itself, it does not necessarily lead to the conclusion that rape is an adaptation. The author intends to refute the adaptationists’ claim that rape is an adaptation.
Proponents of the rape adaptation theory argue that rape is a behavior adapted through natural selection because it is advantageous for human individual survival and gene transmission. An adaptation refers to a mechanism in which a trait or behavior is formed as a result of natural selection and has developed genetically to provide an advantage for survival or reproduction. For example, the human tendency to store as much excess energy as possible is a classic example of an adaptation. The argument is that in resource-scarce environments, this mechanism evolved because storing as much ingested energy as possible was advantageous for survival. Adaptationists apply this same logic to rape. They argue that men who found it difficult to engage in consensual sexual relations turned to rape to pass on their genes, and that this behavior became established as an adaptation because it was advantageous for reproduction.
However, a closer look at the actual patterns of rape crimes reveals that this explanation alone is insufficient. If the purpose of rape were individual preservation and reproduction, the targets would have to be concentrated on women of childbearing age. In reality, however, sexual violence against women who are not of childbearing age occurs consistently and accounts for a significant proportion of cases. Furthermore, there are numerous instances of married men—who already have spouses and can produce offspring through normal sexual relations—committing rape. These facts are difficult to reconcile with the claim that rape is an adaptation aimed solely at individual preservation and reproduction. Therefore, the adaptationist argument—that rape evolved as an adaptation for the purpose of individual preservation—struggles to provide a sufficient explanation when these counterexamples are considered.
In response to this rebuttal, adaptationists explain that forms of rape other than those targeting women of childbearing age are byproducts of adaptation. A byproduct refers to a result that arises when a mechanism interacts with the environment. For example, a mechanism for storing excess energy is an adaptation, but obesity in modern society can be viewed as a byproduct resulting from the combination of an environment characterized by abundant food and insufficient physical activity. Using this logic, adaptationists argue that rape not directed at women of childbearing age is the result of the interaction between the rape mechanism and the environment or other mechanisms. In other words, regarding sexual relations, they argue that a mechanism specifically aimed at rape exists, and that other forms of rape are byproducts resulting from the influence of the external environment or other mechanisms. They contend that rape of women outside their fertile period is the result of their status as relatively less resistant targets, while rape by married men can be explained by the interaction with a mechanism that makes them feel a greater attraction to young women.
Assuming that a mechanism specifically aimed at rape actually exists, the adaptationists’ counterargument could be somewhat persuasive. But can we really assume that such a mechanism exists? If rape is an adaptation, as the adaptationists claim, then the primary mechanism related to sexual intercourse must be rape. In that case, consensual sex could be viewed as a byproduct of the rape mechanism. In reality, however, consensual sex occurs far more frequently than rape. If a single mechanism produces various outcomes, it is more reasonable to view the most frequent outcome as the mechanism’s original purpose. This is because having a mechanism suited to the most frequently encountered situation is advantageous in terms of efficiency. Therefore, rather than viewing rape as the primary purpose of the sexual mechanism, I believe it is more reasonable to view sexual desire as the fundamental mechanism underlying sexual behavior—including consensual sex, which occurs far more frequently—and to regard rape as a byproduct that may arise in that process.
In response, adaptationists might counter that rape and consensual sex are distinct mechanisms. If rape and consensual sex were independent mechanisms, various forms of rape that do not target women of childbearing age could be explained as byproducts of the rape mechanism. However, this argument contradicts the adaptationists’ existing logic. If consensual sex is an adaptation, it implies that it became an adaptation because it is advantageous for individual survival and reproduction. Yet adaptationists previously argued that rape became an adaptation because it is more advantageous for spreading genes than consensual sex. In other words, they have defined rape as the primary mechanism underlying sexual relations. If so, it is difficult to maintain consistency with their existing logic by claiming that rape and consensual sex are each independent adaptations.
Does this mean, then, that I am arguing that consensual sex is an adaptation and rape is its byproduct? My view is slightly different. I view sexual desire—that is, the desire to pass one’s genes on to the next generation—as an adaptation in itself, and I see both consensual sex and rape as byproducts that emerge as this mechanism interacts with the environment. The primary reason I regard both behaviors as byproducts of adaptation is that human decision-making intervenes in the process. It is easy to see that consensual sex, as the name implies, is the result of the parties’ mutual consent. Human decision-making also plays a role in rape. A man looks at a woman, feels sexual desire, and wants to have sex with her. He then considers various factors—such as whether he can overpower her, if there are people nearby, and the risk of being caught—and decides whether to commit rape based on his own values and judgment. In other words, rape is the result of a decision that synthesizes various environmental factors and personal judgment. If there are many people around or if the victim puts up strong resistance, the perpetrator is highly unlikely to attempt rape. Thus, rape can be viewed as a human choice made after evaluating various environmental conditions and as a behavior resulting from a decision-making process.
Once human decision-making comes into play, it is difficult to view this phenomenon as purely genetic. Human judgment is significantly influenced by various environmental factors, such as upbringing, education, social environment, culture, and personal values. Of course, it is true that humans have biological drives such as sexual desire, but how those drives are translated into action is influenced by individual choice and social norms. Therefore, it is not appropriate to view all behaviors that reflect human agency as genetically determined adaptations.
If rape is not an adaptation, then how should it be understood? From an adaptationist perspective, I believe it is more valid to view rape as a byproduct rather than an adaptation. Rape and consensual sex follow quite similar processes up until the point of decision-making. In both cases, a man sees a woman, feels sexual desire, and then considers environmental factors. After that, a choice is made: whether to make an effort to obtain the other person’s consent or to commit a crime. In other words, the process leading up to the decision is a biological process that occurs naturally, independent of an individual’s will, but the subsequent behavior leads to different outcomes for each person. If we consider only this naturally occurring process to be a “mechanism,” it would be more appropriate to view it as a mechanism related to sexual desire rather than a mechanism of rape. Furthermore, since the subsequent behavior is the result of a combination of the external environment and the individual’s judgment, it is reasonable to understand it as a byproduct rather than an adaptation.
Adaptationists argue that rape is a genetic phenomenon and therefore a matter of fact, not one of moral judgment. However, the story changes if rape is viewed as a byproduct of the sexual desire mechanism. Rape is the result of a combination of various environmental factors—such as social institutions, education, upbringing, culture, and personal values—and reflects human decision-making in that process. Therefore, rape cannot be defined simply as a matter of fact unrelated to moral judgment. Since rape is a behavior involving human choice, it is also a matter of values that requires discussion of ethical and social responsibility. However, from the perspective of the interaction between the biological mechanism of sexual desire and environmental factors, there is certainly room to approach it as a subject of scientific research.
The debate over whether rape is an adaptation remains significant today in terms of how we understand and prevent sexual violence. Advocates of adaptation theory likely argued that rape is an adaptation in an attempt to explain this issue scientifically. While the approach of seeking a scientific understanding of social phenomena is certainly meaningful, a synthesis of research findings to date does not provide sufficient grounds to conclude that rape is an adaptation selected for humans through evolution. Rather, I believe it is a more persuasive interpretation to understand rape as a byproduct resulting from the combination of the evolutionary mechanism of sexual desire, various environmental factors, and human decision-making. Furthermore, we must also consider that rape is a crime and a serious violation of human rights, and that scientifically investigating its causes is entirely distinct from justifying or mitigating responsibility for the act itself.
