In this blog post, we will examine the basic concepts and limitations of the theory of kin selection presented in Richard Dawkins’ ‘The Selfish Gene’, and explore how environmental and historical factors can be used to supplement animal behaviors that are difficult to explain solely through kinship ties.
How Is the Theory of Kin Selection Explained?
The book ‘The Selfish Gene’ was written by Richard Dawkins to explain the theory of the selfish gene, a perspective within evolutionary theory. The theory of the selfish gene is a framework for explaining biological behavior that centers on the replication and transmission of genes during the evolutionary process; in the book, Dawkins uses this perspective to explain a variety of behaviors exhibited by individuals, including those that appear altruistic at first glance. However, several points of contention can be raised, such as the issue of applying game theory—which is typically applied to humans—to animal behavior; criticisms of the handicap theory; the problem of defining “genes”; the ambiguity of meme theory, which is based on the similarities between living organisms and culture; and overly extreme expressions. In this article, in particular, I would like to focus on one of these: kin selection theory. While kin selection theory appears to provide a highly convincing explanation for the behavior of related individuals by applying the theory of the selfish gene, in reality, there are quite a few phenomena that are difficult to fully explain with this theory alone. This paper begins with the observation that Dawkins himself did not adequately address such exceptions in his book. Therefore, this article aims to examine the need to supplement the theory of kin selection—which fails to fully account for the behavior of related animal individuals—by considering environmental factors and historical context.
Before explaining Dawkins’ theory of kin selection, let us first examine the “selfishness of genes” on which he bases his argument. The “selfishness of genes” that Dawkins asserts does not mean that genes possess the ability to think like humans—that is, that they think, “I must seek my own benefit,” and act accordingly—but rather refers to a tendency, maintained through natural selection, to ultimately produce as many copies of themselves as possible. Based on this, since individuals related by blood to a specific individual share a certain degree of genetic similarity with that individual, behaviors carried out for the sake of “kin”—such as parents devoting themselves to their children or grandchildren, or children helping their parents and grandparents—can be viewed, from the genes’ perspective, as “selfish” behaviors, that is, actions that contribute to the transmission of more copies of their own genetic material. The concept that represents the genetic relationship between individuals is called relatedness; the relatedness between a parent and a child is 1/2, and the relatedness between siblings is also, on average, 1/2. Using this, the relatedness between a given individual and their grandchild (who is the individual’s child) is 1/2 × 1/2 = 1/4, and the relatedness between a given individual and their cousin (who is the child of a sibling of the individual’s parent) is 1/2 × 1/2 × 1/2 = 1/8. Therefore, assuming that a particular behavior confers a benefit of 1 to an individual, performing that behavior contributes to the benefit of one’s own genetic copies by a factor of 1; performing it for one’s offspring, parents, or siblings contributes on average by a factor of 1/2; performing it for one’s grandchildren or nieces and nephews contributes on average by a factor of 1/4; and performing it for one’s cousins contributes on average by a factor of 1/8. The basic approach of kin selection theory is to calculate the impact of a specific behavior on multiple individuals by considering the genetic relatedness to each individual and to explain the evolutionary conditions of that behavior based on these results. In contemporary discussions of kin selection and inclusive fitness, this approach—which takes genetic relatedness and costs and benefits into account—is treated as an important theoretical framework.
One point to keep in mind when calculating net benefit is that, when explaining kin selection theory in simplified terms, the relatedness of an individual to a non-kin is considered to be 0. Of course, if interactions with unrelated individuals benefit the individual in question or its relatives, that effect can be included in the calculation; however, the direct impact on the unrelated individual itself is not counted as a genetic benefit for that individual.
As mentioned earlier, genes have no thoughts or intentions; however, to ensure a smooth explanation, they will be described as if they possess a purpose. Therefore, whenever a description of purpose appears, it should be understood that this is not the will of the gene but rather a tendency that has emerged through natural selection. For example, the statement “Since genes aim to benefit kin…” can be understood to mean that, when there were genes that influenced behavior to benefit kin and those that did not, the genes that contributed to leaving more copies of themselves became more widespread and preserved through natural selection, while the frequency of the other genes relatively decreased.
What are the limitations of kin selection theory?
First, an important issue to consider when applying kin selection theory directly to the behavior of actual individuals is that individuals cannot accurately determine the degree of kinship between themselves and other individuals. While there are relatively clear-cut cases—such as when a female knows her genetic relationship to the offspring she has borne—it is difficult for a male to be certain that the offspring born to a female are his own without genetic testing. Nor can offspring always accurately determine which individual is their parent. Therefore, while theoretically the kinship between a male and his offspring is 1/2, if we assume that the female mated with several different males before giving birth and that each male has an equal chance of being the father, the probability that a specific male is the father of that offspring is 1/2; consequently, the genetic relationship that the male can expect at the time of decision-making may, on average, be as low as 1/4. This uncertainty generally increases as the generational gap widens, and it is difficult to determine the exact degree of kinship when an individual lacks information to directly verify its actual genetic relationship with other individuals. Behaviors designed to reduce this type of uncertainty include males preventing other males from accessing females, or making eggs distinctive in shape to create a noticeable difference from those of other birds, thereby preventing the rearing of chicks from other species. However, even these behaviors do not provide a means of perfectly determining kinship.
There are other cases that make determining kinship difficult. A prime example is brood parasitism, in which a cuckoo lays its egg in another bird’s nest. As a result of brood parasitism, the original mother bird of the nest ends up providing food and protection to the cuckoo chick—with which she has almost no genetic relationship—at a level similar to that given to her own offspring. From the perspective of a simplified net benefit calculation, this situation—unlike investing in one’s own offspring with high relatedness—involves expending resources to provide benefits to an individual of another species with almost no genetic relationship; therefore, it can lead to a disadvantageous outcome in terms of an individual’s inclusive fitness. Consequently, the theory of kin selection alone cannot fully explain why such behavior occurs.
The second issue concerns behaviors such as adoption, in which an individual provides a level of care similar to that given to a blood relative to another individual with whom there is almost no kinship. Looking at the previous examples, determining kinship itself becomes an issue. So, if we assume an ideal population where technology has advanced to the point where the genetic information of every individual on Earth can be identified, allowing each individual to accurately recognize their kinship with every other individual based on that information—or, alternatively, a population where the phenomena described above do not occur at all, leaving no uncertainty regarding kinship—would it be possible to predict all behavior through a net benefit calculation based on kin selection theory? Considering behaviors such as adoption or moral actions that have no direct relationship to relatedness, it would be difficult to conclude that this is the case. If we assume that an adopted individual acts solely according to the selfishness of genes, the costs associated with caring for an individual with whom they have no genetic relationship are likely to exceed the genetic benefits gained through adoption. Similarly, altruistic behavior toward strangers with whom one shares almost no relatedness may be difficult to explain through a simple net benefit calculation based on kin selection alone.
Dawkins does address cases that cannot be explained by relatedness alone by considering context or environment; examples include discriminatory behavior observed among siblings with the same relatedness. This article focuses on aspects that Dawkins cited as examples in his explanation of kin selection theory but which, in my judgment, lack sufficient explanation regarding their causes and conditions.
How can we supplement the explanation of behavior among related individuals?
Through the issues listed above, we have confirmed that Dawkins’ theory of kin selection alone cannot adequately predict or explain certain animal behaviors. Dawkins himself was aware of some of these problems and mentions them in his book; however, he merely acknowledges the existence of such exceptions without providing a sufficient explanation of the underlying principles behind these behaviors, which makes it seem as though he cannot explain them at all. However, considering that we generally do not find the behaviors listed above strange, we can expect that, with appropriate refinements, it should be possible to explain the principles underlying behavior among related individuals. As a means of refinement, we will examine both the approach of considering environmental and historical influences and the principle—also explained in the book—of how genes influence an individual’s behavior.
Genes have neither thoughts nor will, nor are they entities that make judgments and act in response to changes in their environment on a case-by-case basis. Depending on genetic differences, genetic variants that confer an advantage for an individual’s survival and reproduction are passed on more frequently, and as a result, they influence the behavior of individuals possessing those genetic traits. Therefore, genes cannot predetermine complex behavioral principles for every situation; rather, various genetic factors that influence simple, fundamental behavioral tendencies can be selected. Furthermore, since genetic makeup does not change immediately in response to the environment during an individual’s lifetime but rather changes across generations, genetic variations that conferred behavioral tendencies advantageous for survival and reproduction in past environments may still account for a significant proportion of the current population. At the same time, there is also the possibility that variants advantageous in the current environment will become more prevalent over the long term through natural selection. Based on this information, we aim to supplement and explain issues that were difficult to account for using kin selection theory alone by taking environmental and historical conditions into consideration.
What happens when we apply this supplementary model to real-world examples?
The first issue to address is adoption. Adoption refers to the act of taking in and raising a young individual with whom one has no genetic relationship; while this behavior is primarily observed in humans, it can also occur when multiple pets are kept together, where individuals care for non-related young. It has even been observed in cases where individuals care for members of different species, such as cats caring for mice. Furthermore, even among primates in the wild—rather than in artificial breeding environments—there have been documented cases where individuals without offspring bring in and care for the young of other families or abandoned young. If they had brought in only abandoned young, this might lead to a discussion of primate morality; however, since cases of bringing in the young of other individuals have also been observed, this behavior cannot be viewed solely as a phenomenon related to morality. To explore the causes of adoption, let’s first examine the behavior of “raising young individuals in one’s vicinity” from a genetic perspective. Individuals with genetic traits that discourage this behavior are less likely to raise their own offspring, and those offspring are less likely to survive unless they are accidentally discovered and cared for by other individuals nearby. As a result, a tendency not to care for one’s own offspring may be difficult to sustain within a population over the long term. On the other hand, for individuals with genetic traits that influence them to care for young, the young individual closest to them is statistically most likely to be their own offspring; therefore, even if they occasionally end up raising a pup that is not their own, they would likely have contributed to reproductive success overall. Therefore, let us assume that most individuals exhibit a tendency to “care for nearby young,” and let us also assume that most individuals exhibit a tendency not to “devote themselves more than necessary to individuals they judge to be unrelated to themselves.” These two tendencies may manifest in opposite directions when an individual without offspring encounters a young individual unrelated to itself. What happens in this situation can be explained by analogizing it to the conflict between the tendency to “eat whatever is available to satisfy hunger” and the tendency to “not eat food that tastes bad.” If an individual finds food on the ground but isn’t very hungry, the latter tendency may be stronger, resulting in the individual not eating that food. However, if the individual is so hungry that it becomes difficult to maintain normal functions—causing the former tendency to outweigh the latter—the individual may end up eating that food, even if it is lying on the ground and is something they normally dislike. Even if one is not severely hungry, if—due to genetic differences or other factors—the innate tendency to “eat whatever is available to satisfy hunger” is excessively strong, or the tendency to “refuse food one dislikes” is relatively weak, one may still end up eating that food.
Looking at the analogy above, we can infer that a similar phenomenon would occur in a situation where two tendencies—one to “raise young individuals in the vicinity” and another to “not devote oneself excessively to individuals believed not to be blood relatives”—are in conflict under similar conditions. Under normal circumstances, the expression of the former tendency would not be very strong, and even in the absence of offspring, there might not be many cases where the former tendency outweighs the latter. However, if the former tendency is expressed very strongly due to genetic differences or other factors, or if that tendency remains relatively strong while the individual remains childless for an extended period, it is reasonable to speculate that behaviors such as adoption might emerge. In particular, in complex societies like human society, or in cases where autonomous thinking is highly developed—as in humans—individuals may choose adoption based on social demands or situational judgments. However, this is difficult to explain through the theory of the selfish gene, and since it deviates from the purpose of this paper—which is to “supplement the incompleteness of kin selection theory by considering environmental factors”—we will not address it here.
Second, I will attempt to explain the imprinting phenomenon using the same method employed to explain the adoption issue discussed earlier. Imprinting is a phenomenon in which a newborn offspring develops the behavior of recognizing the first object it encounters during a specific sensitive period as a parent or a conspecific. Let us simplify the tendency that triggers this as a genetic predisposition to “recognize the first large, moving object seen after birth as a parent.” In fact, in experiments designed to explain or observe imprinting, objects such as animal models are sometimes placed near newborn offspring to encourage them to follow or recognize the object as a parent-like figure; in such situations, outcomes that are clearly disadvantageous to the offspring may occur. However, in a typical natural environment, the large, moving object encountered for the first time after birth is highly likely to be the actual parent. Therefore, rather than a “gene that recognizes the first large object seen after birth as a parent” or a “gene that recognizes the first moving object seen after birth as a parent,” it is more plausible that a tendency to select a specific object by combining multiple conditions would have been more advantageous for finding the actual parents. This is because, in the first two examples, the likelihood of mistakenly recognizing other nearby objects as parents—or other moving individuals, such as siblings, as parents—could be relatively higher. Consequently, we can surmise that individuals with a tendency to “recognize the first large, moving object they see after birth as their parents” would have been highly likely to find their actual parents who would care for them; as a result, this behavioral tendency would have conferred an advantage for survival and reproduction, allowing it to be maintained across generations.
Conclusion
In this blog post, we examined an explanation of Dawkins’ theory of kin selection and its limitations, and explored the possibility of supplementing this theory by considering environmental factors—such as adoption and imprinting—as a complementary approach. Theories of kin selection and inclusive fitness remain among the key research frameworks for explaining evolutionary biology and the evolution of social behavior today; however, not all social behavior can be explained by kinship alone. The actual occurrence of behavior may involve the interplay of various factors—including genetic relatedness, costs and benefits, ecological conditions, individual experience, and the social environment—rather than genetic relatedness alone. Therefore, rather than viewing kin selection theory as a theory that completely predicts specific behaviors through a single formula, it should be understood as a theoretical framework that demonstrates how natural selection can explain cooperation and altruistic behavior among related individuals. This paper did not conduct quantitative analyses such as net benefit calculations, and due to the limited research period, many of the cases presented as evidence were largely based on thought experiments and assumptions. Consequently, it is difficult to say that the credibility and generalizability of the proposed explanation are fully guaranteed. In future research, if observational data on actual animal behavior, experimental results, and analyses that quantitatively compare costs and benefits are examined together, it will be possible to determine more specifically to what extent an explanation combining kin selection theory with environmental factors can account for actual animal behavior.
