In this blog post, I will examine the meaning of behavioral evolution and adaptation based on the debate raised in ‘Darwin’s Table’—specifically, “Is rape an evolutionary adaptation?”—and organize my thoughts on the matter.
The Concepts of Rape and Adaptation
On ‘Darwin’s Table’, two groups—one supporting and one opposing the thesis that “rape is an adaptation”—engage in a debate. However, as the debate intensified, it devolved into personal attacks, and the moderator abruptly shifted to another topic, bringing the discussion to a close without reaching a clear conclusion. So, is rape truly an adaptation? I lean slightly toward the “yes” side on this issue.
The key terms I will address are “rape” and “adaptation.” Rape generally refers to sexual acts performed without the other party’s consent. Adaptation refers to the process—or the result—by which an organism undergoes morphological, physiological, or behavioral changes to suit its environment. While adaptation has various meanings, I will focus my discussion here on the evolutionary biological definition of adaptation—that is, changes made to suit the environment.
Can Rape Be Viewed as an Evolutionary Adaptation?
First, to answer the question “Is rape an adaptation?”, we need to examine rape not only as a violent act but also from the perspective of sexual behavior, as suggested in this book. If we view rape solely through the lens of violence, our analysis will be limited to a moral judgment that it is simply “bad behavior,” making it difficult to analyze from an evolutionary perspective. Therefore, rape must also be examined from the perspective of sexual behavior related to reproduction.
Rape can generally be seen as occurring among men who have been unable to find a mate. In other words, it is behavior in which a man attempts to have forced sexual intercourse with an unwilling woman to overcome an environment where he cannot engage in sexual relations for the purpose of reproduction. From this perspective, it can also be interpreted as instinctive behavior aimed at reproduction. However, based on this aspect alone, it is difficult to conclusively label rape as an adaptation.
Therefore, let’s consider the following scenario. Imagine a world where rape does not exist. In that world, all sexual relations are based on mutual consent, and reproduction also takes place within such relationships. However, suppose there is one man who ultimately fails to find a mate and thus loses the opportunity to reproduce. If rape were his only remaining option, he might attempt to have sex by force.
The key question here is why that man was unable to find a mate. It may be because he did not meet the criteria preferred by women. These criteria could include physical appearance, as well as various other factors such as personality or social skills. If that man had not committed rape, he would not have been able to reproduce as long as he remained unable to find a mate. If this were to happen repeatedly to many individuals, they would likely be weeded out through the process of natural selection from an evolutionary biology perspective.
Conversely, let’s assume he produced offspring through rape. In that case, the children who inherit his genes are likely to inherit some of his traits. One could argue that if traits that make it difficult to find a mate are passed down genetically, the offspring may also find themselves in similar situations, and as a result, the behavior of rape could be repeated. From this perspective, it is possible that rape acted as a reproductive strategy and was maintained as a behavior that helped individuals adapt to their environment.
The Counterargument: Rape Is Not an Adaptation
However, those who argue that rape is not an adaptation claim that it actually hinders reproduction. They argue that rape victims may suffer severe psychological trauma, and even if pregnancy occurs, it may result in miscarriage or abortion, or the victim may be unable to raise the child after birth. They also explain that humans have an inclination toward ethical behavior, and that actions violating these social norms are disadvantageous for long-term survival and reproduction.
At first glance, these arguments seem persuasive. However, there are other aspects to consider. First, victims do not necessarily suffer a miscarriage, choose to have an abortion, or kill their child. While such cases exist, it is difficult to view them as representative of all situations. Furthermore, given the advancements in modern medical technology, it is difficult to assume that the same choices existed in the evolutionary environments of the past. Therefore, I believe there are limitations to directly applying the institutions of modern society when discussing the evolutionary process spanning tens of thousands of years.
Additionally, maternal instinct exists among human instincts. To illustrate this, consider the case of surrogacy. Surrogacy is a process in which a third party carries and gives birth to a fertilized egg. Genetically, the child belongs to the commissioning couple, but it is not uncommon for the woman who gave birth to also feel an attachment to the child she bore. How to define parenthood remains a topic of ongoing debate. Considering this, it is reasonable to speculate that the experience of childbirth itself may contribute to the formation of strong maternal instincts. Therefore, I believe it is difficult to conclusively assert that the survival rate of children conceived through rape is necessarily low.
Furthermore, rape is characterized by the fact that the perpetrator can choose their victim regardless of the victim’s consent. Generally, people tend to reproduce with partners who share similar environments or circumstances. However, in the act of rape, the perpetrator unilaterally selects the victim. How this characteristic might affect reproduction is also a subject of discussion from an evolutionary biological perspective.
Child Sexual Assault and the Byproduct Theory
On the other hand, based on cases of sexual assault against children—who are incapable of pregnancy—a counterargument may be raised: if rape is an adaptation, why does it occur even against targets unrelated to reproduction? ‘Darwin’s Table’ also introduces this view and presents the byproduct theory, which explains it as a byproduct of sexual desire.
However, I believe this, too, is likely a byproduct that emerged during the adaptation process. If rape is an adaptation, the targets may vary as the adaptation process unfolds. While most cases would likely be selected to target adults capable of reproduction, other forms of behavior might emerge in some instances. From this perspective, I believe there is a possibility that child sexual abuse can be interpreted as a byproduct arising from the adaptation process.
Furthermore, if rape were merely a byproduct of sexual desire, it should appear in the same way among other animals that possess sexual desire. However, there are animals for which this is not the case. A prime example is the bonobo. Bonobos are known to use sexual intercourse not only for reproduction but also for various other purposes, such as forming social bonds and resolving conflicts. Nevertheless, there are almost no reports of forced sexual intercourse of the kind observed in humans. Of course, this single example does not prove that rape is an adaptation. However, I believe it serves as evidence that it is insufficient to explain rape solely as a byproduct of sexual desire.
Conclusion
Whether rape is an evolutionary adaptation remains a topic of ongoing debate in evolutionary psychology and evolutionary biology today, and there is no consensus within the academic community. In particular, interpreting human behavior as an adaptation is far more complex than interpreting morphological adaptations, and it is not easy to distinguish whether a given behavior is actually the result of natural selection or merely a byproduct of another adaptation.
Furthermore, research continues on the extent to which behavior is heritable. Behavioral genetics has studied the heritability of behavioral traits using monozygotic and dizygotic twins, and various studies suggest that genetic factors may play a role in behavior. However, there remains significant debate regarding whether a specific complex social behavior can be definitively classified as a single adaptation.
Based on the logic presented in the main text, I have examined the possibility that rape could be an adaptation. However, this is merely an exploration of the possibility of an evolutionary explanation; this discussion does not imply that the crime of rape is justified or ethically acceptable. It is clear that in human society, rape is a serious crime and an act that can never be permitted legally or ethically.
