In this blog post, I will present a proofread and edited version of my analysis of the question “Is rape an adaptation?” from an evolutionary biology perspective, based on Stephen Jay Gould’s “Full House Theory.”
It has been over 160 years since Charles Darwin proposed the theory of evolution in ‘On the Origin of Species’. While this may seem like a very long time from a human perspective, it is a very short period on the evolutionary timescale. Of course, meaningful changes may occur in organisms with a generation time of less than a year, but since the generation time for most organisms ranges from several years to several decades, this period is too short for evolutionary changes to accumulate sufficiently. Interestingly, although the concept of “generation time” is a crucial element in understanding evolutionary theory as a whole, it has long been overlooked. However, biologist Stephen Jay Gould used this temporal perspective to interpret adaptation as a more realistic concept than previously understood and presented a new way of viewing evolution. The question that was the topic of this discussion—“Is rape an adaptation?”—can also be analyzed more systematically through the “Full House Theory.” To do so, let’s first examine the core tenets of the “Full House Theory.”
The “Full House Theory” can be summarized in a single sentence: “Evolution is not progress but an increase in diversity.” Of course, it is difficult to fully understand the “Full House Theory” based on this single sentence alone. Therefore, we will examine it in detail using the case study “Why Have .400 Hitters Disappeared?” introduced in Stephen Jay Gould’s book ‘Full House’. It may seem somewhat surprising that I’m using baseball—rather than a biological species—as an example. Of course, baseball isn’t a living organism, but it serves as a very useful case study because a wide variety of records have been accumulated over a long period and organized into a database, and because the patterns of change can be analyzed through the fixed cycle of the season. In particular, while batting average may appear to be a metric that simply reflects a batter’s ability, it actually reflects both the caliber of pitchers and the overall level of competition in the league, making it well-suited for examining changes across the entire population.
How has this batting average changed over time? Ultimately, the league’s average batting average has not deviated significantly from around .260 for a long period. Of course, rule changes favoring either pitchers or batters occurred during specific periods, and—much like the evolutionary process of living organisms—temporary fluctuations arose due to external factors such as environmental changes. Nevertheless, the average batting average has remained relatively stable over the long term. So, how have the batting averages of the league’s top hitters changed? Interestingly, the top batting averages have actually shown a gradual downward trend. In other words, while the league-wide average has remained stable, the highest individual records have declined. The core of the “Full House Theory” is that this indicates an overall improvement in the league’s standard. Many baseball commentators explain the disappearance of .400 hitters by citing reasons such as: “First, there aren’t as many outstanding hitters as there used to be. Second, players are overworked due to the commercial environment of modern baseball. Third, pitchers’ skills have improved. Fourth, defensive capabilities have improved. Fifth, data analysis and team management capabilities have advanced. “Sixth, media and public attention place a burden on players.” However, the “Full House Theory” explains all these phenomena much more succinctly within a single framework.
From the perspective of this “Full House Theory,” let’s examine the topic of this discussion: “Is rape an adaptation?” Looking back from my perspective as a participant in the debate, it appears that both sides had different understandings of the very definition of “adaptation,” and since both definitions were concepts that had been used to some extent in existing evolutionary biology, the debate seemed to run along endless parallel tracks. Just as the “Full House Theory” summarized the various explanations offered by baseball commentators into a single principle, it can also help clarify this confusion more clearly.
In the “Full House Theory,” adaptation refers not to the temporary benefit of an individual but to the process by which the level of the entire group improves. The theory posits that because batters steadily improved and adapted to the league’s level, and pitchers simultaneously improved alongside them, the average batting average was able to remain around .260. If only one side—batters or pitchers—had improved, the average batting average would have shifted significantly, either rising or falling. However, that was not the case in reality. Ultimately, both sides improved their performance through adaptation, and as a result, an environment has been created in which a .400 hitter—once a symbol of superiority—is unlikely to emerge.
Let’s assume that rape is an adaptation by men to spread their genes as widely as possible. Of course, regardless of this, humanity’s overall reproductive capacity has increased significantly throughout history, and the world’s population has also grown over the long term. If rape were indeed an adaptation that favors reproduction, women would have had to evolve corresponding adaptive mechanisms to counter it. However, this claim is not accepted as an established fact in current evolutionary biology, and the view that explains rape as a human adaptive strategy has also been the subject of significant controversy in academic circles. Furthermore, in modern society, due to various factors—such as the development of laws and institutions, sociocultural changes, and the widespread use of contraception—the proportion of births resulting from rape shows a consistent downward trend compared to the past. Considering these points, it is difficult to conclusively assert that rape is a human adaptation.
The core of the pro-side’s argument in the debate was that “if it was an adaptation in the past, it can still be called an adaptation even if it is not one today.” This may hold some merit in certain interpretations of traditional evolutionary theory centered on natural selection. However, from the perspective of the “Full House Theory,” this argument lacks persuasiveness. This is because adaptation is a process that continuously changes over time and across environments, and traits that were advantageous in past environments cannot be assumed to hold the same significance today. Therefore, even taking these points into account, the “Full House Theory” adopts a cautious stance toward interpreting rape as an adaptation.
Finally, one might consider the counterargument that rape is declining because it has gradually been curbed by social institutions and has become more risky. In fact, laws and institutions are cultural and social mechanisms created by society as a whole, and they differ in nature from biological adaptations. Furthermore, the question has been raised as to whether rape might confer a certain evolutionary benefit on women, given that it facilitates the transmission of genes. However, this argument fails to adequately account for various biological, psychological, and social factors—not to mention the fact that it infringes on women’s right to choose a mate. Therefore, interpreting this as a simple adaptive strategy is a highly limited approach.
While conducting the discussion titled “Is Rape an Adaptation?”, I was surprised to find that some view the phenomenon of rape far too lightly, given the severity of the crime. Of course, the attempt to analyze a phenomenon from various academic perspectives is meaningful in itself. However, rape is a very serious violent crime, and explaining it solely through the framework of evolutionary adaptation can raise many ethical and social issues. If spreading one’s genes is an adaptation, this raises the question of whether all other extreme crimes committed for the same purpose must also be explained as adaptations. Furthermore, if the logic of the proponents is applied literally, it becomes possible to argue that all violent behaviors that existed in the past—even if they have since disappeared—were adaptations. Ultimately, if taken to its extreme, this logic carries the risk of interpreting even crimes such as murder as adaptations. However, the existence of a crime and whether it constitutes an evolutionary adaptation are not the same issue. Therefore, we must approach the assertion that rape is an adaptation with caution, and I conclude this article with the hope that humanity will build a society that is increasingly free from such crimes.
