Empirical Findings for Inclusive Fitness Theory

Inclusive fitness theory, also known as kin selection theory, proposes that organisms are more likely to engage in altruistic behaviours towards their genetic relatives because it increases their inclusive fitness, a measure of their overall reproductive success. The theory is based on the premise that an organism's genes are more likely to be passed on to future generations if they help close relatives survive and reproduce, as close relatives share a higher proportion of an individual's genes than non-relatives. Therefore, by helping a close relative to survive and reproduce, an organism can indirectly promote the survival and reproduction of its genes.

Empirical Findings that Support the Implications of Inclusive Fitness Theory

What are the Empirical Findings that support the implications of inclusive fitness theory?

Empirical Findings hold great importance in supporting the hypothesis of the Theory. Several findings supporting inclusive fitness theory and its applications include warning sounds given by squirrels when sensing danger up ground, Eusociality in insects, especially in bees, and also several adaptations among humans, such as helping raise offspring of genetically related siblings, prioritizing helping kin members.

According to the inclusive fitness theory, one of the leading hypotheses is that people are more likely to behave altruistically toward near relations, with the degree of relatedness dictating the level of altruism.

Numerous investigations on various animals, from insects to primates, have confirmed this hypothesis. For example, in a study of cooperative breeding in the red fox, researchers found that females were more likely to help raise their sisters' offspring than unrelated females. Similarly, in a study of cooperative feeding in vampire bats, researchers found that bats were likelier to share food with close relatives than non-relatives.

Following are some critical empirical findings that support the implications of inclusive fitness theory −

Alarm Calling in Ground Squirrels

Belding's ground squirrels provide an excellent example of how altruistic behaviour can evolve through inclusive fitness. By emitting alarm calls in the presence of predators, squirrels put themselves at risk of being attacked. However, this behaviour benefits their genetic relatives by alerting them to the danger and helping them escape. Biologist Paul Sherman conducted a study to test three hypotheses about this behaviour: predator confusion, parental investment, and inclusive fitness.

The study results showed that the predator confusion hypothesis was ruled out, leaving only the parental investment and inclusive fitness hypotheses. Female ground squirrels, with a higher potential for parental investment, were found to emit alarm calls more often than males. This finding is consistent with parental investment and inclusive fitness hypotheses, as their genetic relatives benefit from the signal.

Additionally, female ground squirrels were found to help their genetic relatives in territorial conflicts but not non-relatives, providing further evidence for the inclusive fitness hypothesis. This study highlights the importance of kinship in the evolution of altruistic behaviour. Inclusive fitness can play a crucial role in developing cooperation in animal societies.

Individuals in many species of ground squirrels will emit alarm calls to alert others of any approaching predators or potential threats above the grounds. However, the likelihood of the predator making a warning call increases the closer it is to a related compared to a non-relative. Since warning relations improves the fitness of both the caller and the cautioned relative, this behaviour is compatible with the expectations of the inclusive fitness theory. Several hypotheses have been advanced to explain this apparent act of altruism −

  • The Predator Confusion Hypothesis − The alarm call might function to confuse the predator by creating a mad scramble in which all the ground squirrels rush around for safety. This confusion might help the squirrels, including the alarm caller, to escape.

  • The Parental Investment Hypothesis − Although the alarm caller is placed at greater risk by sounding signal, perhaps their children are more likely to survive. The alarm call might function as a form of parental investment.

  • Inclusive Fitness Hypothesis − Although the signaller might suffer in the currency of survival, the squirrel's aunts, uncles, brothers, sisters, father, mother, and cousins all benefit. According to this hypothesis, the signal alerts the "vehicles" that contain copies of the squirrel's genes, providing an inclusive fitness benefit.

Kin Recognition and Kin Classification in Humans

Human recognition of kin is essential for many social behaviours, including parental care, kin altruism, inbreeding avoidance, and optimal outbreeding. This recognition is facilitated by various mechanisms, including early association with kin during infancy, olfactory cues, kin terminology, physical similarity, and a "universal grammar" of social cognition. These mechanisms allow humans to identify potential givers and receivers of altruism based on kinship value.

Studies have shown that humans can detect kinship not only among close family members but also among strangers or groups of people who are not related to them. This ability is critical for solving significant adaptive problems, such as identifying potential allies or avoiding antagonizing those with formidable kin. The empirical evidence supports the idea that kinship is a fundamental social category humans use to navigate their social world and make decisions about adaptive actions such as altruistic and self-sacrificing behaviour.

Patterns of Helping in the Lives of Los Angeles Women

In a study of 300 adult women in Los Angeles, researchers tested inclusive fitness theory and found that helping exchanges were more likely to occur with close kin than distant kin. This supports a key prediction from inclusive fitness theory. The study also found that women were more likely to help their children, nieces, and nephews than vice versa, reflecting the greater future reproductive potential of the younger recipients.

However, it is essential to note that many acts of helping were received from and directed toward close friends. While these findings are limited to one sex, one city, and one method of information gathering, other studies have extended these findings to different populations and methodologies.

For example, a study of 11,211 South African households found that the degree of genetic relatedness predicted how much money was spent on children's food, health care, and clothing, and a study of the Pimbwe, a Tanzanian horticultural population, found that the larger the size of the maternal kin network, the healthier the children and the lower their mortality rate.

Life-or-Death Helping among Humans

Burnstein, Crandall, & Kitayama (1994) conducted a study to test hypotheses derived from inclusive fitness theory regarding the relationship between helping behaviour and genetic relatedness. The researchers proposed that helping would be based on the recipient's ability to enhance the helper's inclusive fitness. They predicted a gradient of helping based on genetic relatedness.

They also suggested that helping would decrease as the recipient's age increased and that genetic relatives of higher reproductive value and offering a better return on investment would receive more help than those of lower reproductive value and lower return. Studies conducted in the United States and Japan using life-or-death situations and daily helping showed that helping decreased as the degree of genetic relatedness decreased, with this pattern being most robust in the life-or-death scenario.

The study supports inclusive fitness theory and highlights the significance of genetic relatedness in shaping helping behaviour. Overall, research on altruism and kinship indicates that genetic relatedness plays a crucial role in predicting helping behaviours, with helping to be more likely towards younger and higher reproductive value genetic relatives. The effects of kinship appear particularly strong, with cultural factors being less influential.

Genetic Relatedness and Emotional Closeness: Is Blood Thicker Than Water?

Recent research suggests that emotional closeness is a crucial mechanism underlying acts of altruism towards genetic relatives. Studies have shown that genetic relatedness strongly predicts emotional closeness and willingness to behave altruistically towards family members, even when controlling for variables such as distance and frequency of contact.

Other indicators of emotional closeness include the frequency of contact, doing favours, and the amount of psychological grief experienced when a child dies. Full siblings frequently contact each other and receive more favours than half-siblings, stepsiblings, or cousins. Parents experience more grief than less genetically related relatives when a child dies, with the death of an elder and healthy child causing the most intense grief.

These findings suggest that emotional closeness may be an essential factor that prompts acts of altruism towards genetic relatives, highlighting the importance of genetic relatedness in shaping human social behaviour.


The implications of inclusive fitness theory are not without controversy, with some researchers questioning its universality and applicability to human behaviour. Further research is needed to fully understand the complex interplay between genetic relatedness, emotional closeness, and the context in predicting altruistic behaviour towards family members.

Overall, while the findings on the role of genetic relatedness in altruistic behaviour are essential, they should be considered in the larger context of the many factors that influence human behaviour.

Updated on: 11-Apr-2023


Kickstart Your Career

Get certified by completing the course

Get Started