Validity and Value of Inclusive Fitness Theories

Darwin's theory of evolution had a revolutionary impact on psychology, similar to Darwin's theory of evolution had a revolutionary impact on psychology, similar to the impact of the theories of Copernicus and Newton. Darwin's ideas encouraged the study of individual differences and behaviour, which led to the development of various fields in psychology.

In addition to the impact of Darwin's theory on psychology, his concept of fitness has also significantly influenced the development of inclusive fitness theory.

What is Inclusive Fitness Theory?

Inclusive fitness theory modifies Darwin's definition of fitness from the survival and reproductive success of the individual to the perpetuation of one's genes, which allows for a broader range of social behaviours to be explained in evolutionary terms. Inclusive fitness theory emphasizes the importance of kin, or genetic relationships, in determining fitness, as helping one's kin survive and reproduce can effectively perpetuate one's genes.

This conception of fitness is central to the field of sociobiology, which has since evolved into the field of evolutionary psychology. Through this lens, evolutionary psychologists attempt to explain human behaviours such as love, altruism, and aggression in terms of inclusive fitness, by examining how they may have evolved as strategies for perpetuating one's genes through kin selection.

Development in the Theory

This concept has been a significant field of study in evolutionary biology ever since it was first put forth by the British scientist W.D. Hamilton in the 1960s. Hamilton asserted that the number of a person's genes handed down to succeeding generations depends on their capacity for reproduction and the effectiveness of their connected relations in reproducing. A person should help their relations effectively reproduce because closer genetic kinship increases the chance that two beings will share genes.

This idea is essential for creatures in social groups, such as ants, bees, and humans. Inclusive fitness also helps explain why individuals would be willing to perform behaviours that benefit the team, even if it means risking their self-lives or sacrificing their reproductive success. In these species, individuals often work together to raise young, defend groups and collect food.

For instance, even though the workers in social animals like bees are sterile and unable to procreate independently, they still labour diligently to collect sustenance for the queen and protect the colony from intruders. The employees are assisting in ensuring the longevity and reproductive success of their genetically linked queen and her progeny, which is how inclusive fitness theory explains this behaviour.

Similar to this, we frequently see people taking care of their elders as well as the nieces and nephews of their brothers. As these people are assisting in ensuring the survival and reproductive success of their near relations who share a significant percentage of their genes, inclusive fitness can also explain this behaviour.

Hamilton's Rule

Imagine a gene that leads someone to act altruistically towards another person to comprehend this definition of inclusive fitness. The term "altruism," as used in this context, is defined as paying the price for another person's benefit while doing so at one's own expense. Hamilton asked: Under what circumstances might a gene for altruism develop and disseminate across the population? Most of the time, we anticipate that altruism will not develop.

Costs to oneself will prevent one from reproducing. Therefore selection will often work against costs to others, many of whom are rivals. On the other hand, Hamilton's insight was that altruism could evolve if the benefit outweighed the costs to the self to the recipient of the altruism, multiplied by the likelihood that the recipient carried a copy of the altruism gene. More precisely, Hamilton's rule states that natural selection prefers systems for benevolence when

c < rb

In this equation, c stands for the actor's cost, r for the actor and recipient's genetic relatedness (defined as the likelihood of having a specifically focused gene in joint with another person over and above the gene's typical population frequency), and b for the recipient's benefit. Reproductive currencies are used to assess both costs and benefits. This formula states that selection will favour an individual incurring costs (being "altruistic") if the benefits to a.50 kin member are more than twice the costs to the actor, a.25 kin member is more than four times the costs to the actor, and a.125 kin member is more than eight times the costs to the actor.

An example will illustrate this point. Imagine passing by a river and noticing some of your genetic ancestors drowning in a raging current. Hamilton's rule states that selection will favour decision rules that result in you jumping into the water to save three of your brothers, but not one. Applying the logic of Hamilton's rule, evolved decision criteria should lead you to give your life for five nieces or nephews, but you would have to save nine first cousins before sacrificing your own life.

Hypotheses about Universal Aspects of Kinship

Hypotheses regarding the universal elements of kinship psychology. To begin, they imply that ego-centred kin terminology will be ubiquitous. In all civilizations, all relatives will be categorised as central individuals. My parents and your parents are not the same people. My brothers are not the same as your brothers. All kin words, in summary, flow from the ego-centred focal individual.

Second, all kinship systems will make meaningful differences based on gender. Moms are distinct from dads and sisters from brothers. When the sex of a kin member has reproductive effects, this sex distinction arises. Moms, for example, are optimistic that they are genetically connected to their children, whilst dads are unsure. Boys can achieve great reproductive success through many matings, while daughters cannot. In brief, the kin member's sex is critical to the adaptive difficulties he or she encounters. Hence all kin systems should discriminate based on sex.

Third, generation is essential. Asymmetrical relationships between parents and children are common. Children, for example, become increasingly valuable vehicles for their parents as they mature, but parents become less and less helpful to their children. As a result, we anticipate that all kin systems will make generational differences. Fourth, kinship links will be uniformly displayed on a closeness dimension.

Moreover, proximity will be strongly connected to genetic relatedness. In brief, emotional (feeling near to someone) and cultural "closeness" recognitions are projected to correspond to genetic closeness. Fifth, their genetic relatedness will determine their kin's degree of cooperation and solidarity. Collaboration and conflict should be foreseeable based on the degree of genetic relatedness between kin members; people should resort to close kin rather than distant kin when it truly counts; and any conflicts of interest should be reduced more among close kin than among far relatives.

Criticisms of Inclusive Fitness Theory

The first criticism is that model of the evolution of social behaviour in colonies is less general than models of competition between colonies. However, this critique has been repeatedly refuted, as inclusive fitness and multilevel selection analyses are different partitioning of fitness and always agree on the direction of selection. Another criticism is that inclusive fitness theory is no more than a conceptually complex reorganization of classical Darwinian/Fisherian fitness. However, this viewpoint has also been refuted, as Hamilton conceived of inclusive fitness theory as an extension of classical fitness.

Other critiques concerned the empirical predictions from inclusive fitness theory, such as the haplodiploid hypothesis and sex ratio theory. However, evidence and theory against the haplodiploid hypothesis had already accumulated, and the attack on sex ratio theory has since been largely resolved. Overall, while there have been criticisms of inclusive fitness theory, these criticisms have primarily been addressed, and the theory remains a helpful framework for understanding the evolution of social behaviour.


The inclusive fitness theory, which highlights the role of genetic similarity in developing traits, has broad implications for fields like conservation biology and the study of complex social relationships. The inclusive fitness theory, which considers individual fitness and family selection, thoroughly explains the factors influencing sexual success in different animals. Inclusive fitness is a fundamental concept in evolutionary biology, but some critics argue that it has limitations and should be replaced by multilevel selection theory.

These critics also question the empirical predictions of inclusive fitness theory, such as those related to sex allocation and the use of statistical concepts to understand responses to selection. However, recent research has addressed these criticisms and demonstrated the usefulness of inclusive fitness theory for understanding social evolution and group adaptations, including the transition to eusociality and multicellularity.

Updated on: 12-Apr-2023


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