In this blog post, I will examine the theory of kin selection as explained by Richard Dawkins in ‘The Selfish Gene’, and explore altruistic and selective behaviors in animals—which are difficult to explain solely through kinship—from the perspectives of environmental factors and social interactions.
Introduction
Richard Dawkins’ ‘The Selfish Gene’ explains the behavior of living organisms, including humans, from the perspective of genes, presenting a view that sees living organisms as entities that replicate genes. In ‘The Selfish Gene’, Dawkins explains that genes tend to replicate themselves in order to be preserved for a long time and spread widely, and based on this perspective, he explains the evolution and behavior of living organisms using various examples. The term “selfish” used here is not meant to imply that genes consciously pursue their own goals, but rather is a metaphorical expression of the fact that, as a result of natural selection, traits favorable to the replication and transmission of genes are passed down through generations. From this perspective, not only selfish but also altruistic behaviors in animals can be explained in terms of their impact on gene transmission and survival.
One of the key concepts Dawkins introduces while explaining animal behavior from the perspective of genes is kin selection. It is more accurate to view this not as a theory originally proposed by Dawkins, but rather as his popular explanation in ‘The Selfish Gene’ of the theories of kin selection and inclusive fitness developed by William Donald Hamilton. Kin selection is the perspective that an individual can increase the likelihood of passing on genes from the same lineage to the next generation by engaging in behaviors that aid the survival and reproduction of genetically closely related individuals. Hamilton’s rule takes into account both the degree of kinship—indicating the closeness of the genetic relationship—and the benefits gained by the recipient, as well as the costs borne by the individual performing the behavior.
Since individuals who are more closely related are more likely to exhibit behaviors of devotion or assistance toward one another, kin selection can serve as an important theoretical framework for explaining social behavior in animals. For example, helping close relatives increases the recipient’s chances of survival and reproduction, which in turn increases the likelihood that genetic traits shared with the helper will be passed on to the next generation. From this perspective, the theory of kin selection appears to explain a significant portion of the behavior observed among related animals.
However, there are certain animal behaviors that are difficult to explain solely by kinship or that cannot be fully accounted for by kin selection alone. Examples of such behaviors include adoption, imprinting, education and learning, reciprocal cooperation, and human moral behavior. In particular, the fact that caregiving, cooperation, and altruistic behavior can occur even among non-related individuals demonstrates that factors other than kinship must also be considered when understanding animal behavior. In fact, altruistic behavior in animals is being studied in conjunction with various conditions, such as reciprocity and social relationships, in addition to kin selection.
Therefore, while kin selection theory serves as an important framework for explaining animal behavior, it has limitations when attempting to explain all selective behaviors based on a single principle. In this paper, we will examine the shortcomings of kin selection theory and explore methods to more consistently understand behaviors between related and unrelated individuals—behaviors that are difficult to explain through kin selection alone. In particular, we will focus on the fact that animal behavior is influenced not only by kinship but also by various environmental factors, such as rearing environment, learning, imprinting, and social relationships.
Dawkins’ Theory of Kin Selection
The behaviors Dawkins explains through kin selection are not so much all general animal behaviors as they are specifically related to devoted and altruistic behaviors observed among related individuals.
Kin selection is based on the premise that behaviors advantageous for genes to pass on as many copies of themselves as possible to the next generation can be maintained through natural selection. Therefore, when explaining the degree of devotion between related individuals, it is necessary to consider how behaviors that aid the survival and reproduction of the other individual ultimately affect one’s own inclusive fitness.
Hamilton’s rule is a commonly used framework for quantitatively explaining kin selection. Hamilton’s rule states that altruistic behavior can be maintained by natural selection if the benefit it provides to the recipient—weighted by the degree of kinship—exceeds the cost incurred by the behavior. This can be simply expressed as rB > C. Here, r represents the relatedness between two individuals, B represents the benefit gained by the recipient, and C represents the cost borne by the helper. Relatedness can be understood as an indicator of the likelihood or proportion of genetic variation shared by two individuals derived from a common ancestor. The relatedness between parents and offspring, or between siblings, is generally 0.5, while that between grandparents and grandchildren is calculated as 0.25.
Therefore, in kin selection, one must not only consider whether a kinship relationship exists but also take into account the degree of that relationship, as well as the costs and benefits resulting from the behavior. Furthermore, in the actual behavior of animals, various factors come into play, such as whether the other individual is actually related by blood, how accurately the individual can recognize such a relationship, and the extent of the survival and reproductive benefits that can be gained through the behavior. For this reason, kin selection is an important explanatory framework for understanding animal behavior, but it should not be understood as a theory that reduces all conditions determining an individual’s behavior to a single variable.
Problems with Dawkins’ Theory of Kin Selection
However, there are selective behaviors that are difficult to explain through kin selection alone. Furthermore, there is a problem in that, when explaining kin selection primarily in terms of relatedness, it is difficult to sufficiently account for the various variables at play in actual natural environments. While kinship, as well as the costs and benefits of behavior, serve as important variables in kin selection, the conditions that determine an individual’s behavior in the natural world are far more diverse. This is because a complex interplay of factors—such as the environment in which the individual grew up, relationships with other individuals, learned behaviors, experiences, social structures, and the specific situations in which behaviors occur—can all come into play. Therefore, to understand animal behavior, it is necessary to examine not only kinship and genetic factors but also these environmental and social factors.
The theory of kin selection has the following problems. First, an individual cannot always accurately determine the extent to which another individual shares its genes. Animals cannot directly calculate the exact degree of kinship with another individual; instead, they obtain the clues necessary for behavior indirectly through physical appearance, scent, behavior, rearing environment, or social relationships. Consequently, even if two individuals are actually closely related, they may fail to recognize each other if they have been separated for a long time or lack sufficient cues for identification. In such cases, a discrepancy arises between actual genetic relatedness and the information an individual uses in its behavior; consequently, it is difficult to explain the behavior based solely on actual relatedness.
Second, kin selection should not be understood solely as a one-sided sacrifice between parents and offspring. Not only the behaviors in which parents invest in their offspring but also the behaviors in which offspring assist their parents or other relatives can be analyzed from the perspective of kinship and inclusive fitness. Since the relatedness between parents and offspring is generally 0.5, behaviors in which offspring help their parents are not inherently excluded from the principle of kin selection. In particular, if a parent’s survival can influence the survival or reproduction of other offspring, behaviors in which adult offspring help their parents can also be analyzed from the perspective of kin selection.
Similarly, even when very elderly parents are unable to directly produce more offspring, it is difficult to simply conclude that “it cannot be explained by kin selection because they can no longer pass on their genes,” given the impact these parents have on the survival of other offspring or relatives they have already produced. This is because kin selection takes into account not only an individual’s direct reproduction but also indirect genetic benefits through relatives.
Third, phenomena such as brood parasitism and imprinting demonstrate that an individual’s behavior may not align with actual kinship ties. In brood parasitism, chicks born in the nests of other species may follow the behavior of the foster parent rather than their biological parents; in some animals, behaviors that recognize parents or peers are formed through experiences immediately after birth or learning during specific periods. In such cases, since individuals can recognize and behave toward specific individuals as parents or social partners regardless of actual genetic kinship, there are limitations to explaining behavior based solely on actual kinship. In particular, if the experiences a young individual has with others during its development influence its subsequent behavior, we must consider not only kinship but also the rearing environment and learning processes. Fourth, altruistic behavior can occur even toward individuals with whom there is no close genetic relationship, such as in cases of adoption, education, or moral behavior. In other words, an individual may help others with whom it has no direct genetic relationship or engage in behavior that incurs a cost to itself. In fact, cooperative and helping behaviors in animals can occur not only within kinship relationships but also in reciprocal relationships; studies analyzing food-sharing behaviors in humans and other primates have also shown that reciprocity is a key factor in helping behavior. For example, when an individual adopts and raises a young animal with which it has no direct genetic relationship, it is difficult to explain this behavior solely from the perspective of kin selection. However, adoption is not always completely unrelated to kin selection. In fact, a study analyzing adoption cases among red squirrels reported that adoption occurred among close relatives and took place when the increase in inclusive fitness gained from adopting a relative outweighed the additional costs of rearing. Therefore, while adoption can be explained by kin selection in some cases, it is difficult to view all adoption behaviors as solely attributable to kin selection. The same applies to education and moral behavior. Individuals learn specific behaviors as they grow up and can develop certain behavioral patterns through exposure to social norms and community expectations. In the case of humans, in particular, people learn the significance of helping others through education and, driven by a sense of mission or a spirit of service, may engage in altruistic behavior even toward non-relatives. Behaviors such as helping someone with whom one has no direct genetic interest, or even sacrificing one’s own safety and life to save another, are difficult to explain fully through kin selection alone. Furthermore, in behaviors such as blood donation, individuals may invest time and effort for the sake of others even when they do not know who will receive their blood. To understand such behaviors, it is necessary to consider factors beyond kin selection, such as social learning, norms, reciprocity, and individual values.
Explaining Animal Behavior Through Kin Selection and Environmental Factors
Therefore, while kin selection is an important factor in explaining the principles of animal behavior, it is difficult to view it as the sole factor. The explanatory power of kin selection may increase in cases where environmental influences are minimal and kinship relationships between individuals have a significant impact on behavior. Conversely, in cases where the rearing environment or early experiences—such as imprinting—strongly influence the formation of behavior, it is difficult to explain behavior based on kinship alone. In addition to genetic relatedness, various environmental factors can influence animal choice behavior, and in actual behavior, multiple factors often act simultaneously. Environmental factors are often difficult to quantify. This is because most behaviors are not explained by a single factor but rather by the complex interaction of multiple factors. It is also not easy to accurately determine the extent to which a specific factor has influenced a particular behavior. Therefore, it can be said that in the selective behaviors of various animals, kin selection and environmental factors may act simultaneously, while in specific situations, the influence of one factor may be more pronounced than the other. The key is not to view kin selection and environmental factors as mutually exclusive explanations, but to consider them together depending on the conditions under which the actual behavior occurs. Reviewing the examples discussed earlier helps illustrate this point. In the case of imprinting, strong environmental factors—such as the rearing environment and early experiences—play a role. Even individuals with no genetic relationship may recognize a specific individual as a parent and exhibit following behavior depending on the environment in which they were born and raised. This behavior demonstrates that the actual genetic relationship may not align with the information an individual uses to determine its behavior. Therefore, to understand imprinting, one must consider not only genetic relationships but also the rearing environment and the learning process. Environmental factors can also play a role in adoption. To understand why new parents behave altruistically toward a child they have adopted, it is necessary to consider not only genetic relationships but also the attachment and social bonds formed through shared living experiences, as well as the experiences of care. At the same time, as discussed earlier, since some adoptive behaviors are directed toward relatives, not all adoptive behaviors can be explained solely by environmental factors. In fact, among the adoption behaviors observed in nature, there are confirmed cases where kinship plays a significant role. Environmental factors and social relationships can also play a significant role in blood donation or other altruistic behaviors toward others. When individuals have received education about moral behavior in the classroom or at home and have developed a firm understanding of it, or when driven by a sense of mission or a spirit of service, they may engage in altruistic acts even toward strangers with whom they share no blood ties. Furthermore, people may engage in altruistic behavior not only for their own genetic benefit but also for their long-term interests or to maintain social relationships. When an individual acts altruistically toward another, a reciprocal relationship may form in which the other person, in turn, provides assistance to the first. Thus, even when individuals are not related by blood, cooperative relationships that benefit both parties can develop based on the social environment and mutual interactions. In fact, reciprocity has been studied as an important factor in helping behavior among humans and other primates, independent of kinship. Of course, in cases where parents act altruistically toward their children by sacrificing themselves and showing devotion, where individuals act altruistically toward close relatives, where grandmothers act altruistically toward their grandchildren, or where siblings care for and help one another, kin selection and environmental factors may interact. Such behaviors do not necessarily have to be explained solely by kin selection. This is because not all parents always act altruistically toward their offspring, and the relationship between parents and children can also vary depending on individual experiences, the environment, and social relationships. There are parents who exploit their children, demand altruistic behavior from them, or even abandon them. These cases demonstrate that actual behavior is not determined by kinship alone. Therefore, even when selection occurs within a kin relationship, it is difficult to conclude that kin selection is the sole factor at work. While kinship is an important condition influencing behavior, the individual’s environment, learned behaviors, relationships with other individuals, and experiences of interaction can all play a role. To explain the principles of animal behavior, it is necessary to use kin selection as an important explanatory framework while also considering various environmental and social factors. The fact that kin selection is a very important theory for understanding social behavior and the fact that not all social behavior can be explained by kin selection alone are not mutually contradictory. In fact, while kin selection and the theory of inclusive fitness have long played a crucial role in understanding the evolution of social behavior and altruism, other studies have also proposed theories that seek to explain social behavior from the perspectives of natural selection, group structure, and reciprocity.
Conclusion
In this article, we examined the selective behaviors of animals that are difficult to explain through kin selection alone, based on the perspective of kin selection described by Richard Dawkins in ‘The Selfish Gene’. While kin selection provides an important explanation for altruistic behavior observed among related individuals, it is not a theory that accounts for all factors determining an individual’s behavior. Helping and cooperative behaviors can occur even among unrelated individuals, and in behaviors such as imprinting, the rearing environment and early experiences can have a more direct influence on behavior than actual kinship ties. Furthermore, while kinship plays an important role in behaviors such as adoption in some cases, in others, social relationships and environmental factors must be considered together. To understand both the selective behaviors of animals within kinship relationships and the behaviors of animals that help and select one another despite lacking a kinship bond, it is necessary to consider kin selection and environmental factors in a comprehensive manner. In some behaviors, kinship and inclusive fitness may play a significant role, while in others, environmental and social factors—such as learning, imprinting, social relationships, and reciprocity—may have a greater influence. Therefore, rather than explaining animal behavior based on a single principle, it is more appropriate to examine the context in which the behavior occurs, the relationships between individuals, the costs and benefits involved, kinship ties, and environmental conditions collectively. Future research should examine a wider range of case studies on animals’ selective behaviors and specifically analyze how environmental factors and kin selection interact in each case. Furthermore, it is necessary to examine which elements are included in environmental factors, identify cases where kin selection exerts a particularly strong influence, and determine under what conditions altruistic behavior emerges among non-kin individuals. As such research accumulates, kin selection and environmental factors will no longer be viewed as mutually exclusive explanations but can instead be comprehensively utilized as one of several explanatory frameworks for understanding complex animal behavior.
