Inclusive fitness

From Academic Kids


In a biological sense:

Inclusive fitness encompasses conventional Darwinian fitness with the addition of behaviors that contribute to an organism’s individual fitness through altruism. An organism’s ultimate goal is to leave the maximum number of viable offspring possible, thereby keeping their genes present within a population. Since relatives of an organism are likely to share common genes, an organism may increase its own fitness by keeping its relatives and offspring viable. Kin selection results from this altruistic behavior towards relatives leading to increased fitness in an organism. Inclusive fitness therefore takes into account both the passing of genes from an organism to its offspring and the inheritance of the same genes among relatives and their offspring.

The most obvious examples of increased inclusive fitness can be observed in the altruistic behaviors of parents. To ensure that their genes remain in the gene pool, organisms attempt to give rise to the maximum number of offspring that are sure to survive. Once the offspring are produced, the parents’ reproductive success is determined by the number of offspring that can then procreate and carry on the family genes. Natural selection therefore favors any genes that code for behaviors that lend themselves to increased fitness. Possibly having a genetic basis, innate behaviors that cause parents to sacrifice their well-being, either in the actually birthing process or in aiding their young, increase the parents’ fitness, which makes them more reproductively successful and therefore favored by natural selection.

Increasing an organism’s inclusive fitness can also involve altruistic behavior towards relatives that have a probability of sharing common genes. For example, Belding ground squirrels give alarm calls to warn the population of ensuing dangers. By emitting the alarm, the Belding ground squirrel puts itself in increased danger by giving away its location. In the process, however, the squirrel protects its relatives that live within the population. In further studies, it has been shown that willingness of the squirrel to put itself at risk is directly proportional to how closely related it is to members of its population. Therefore, if protecting the other squirrels in the immediate area will lead to the passing on of more of the squirrel’s genes than the squirrel could leave by reproducing on its own, the squirrel is willing to sacrifice itself, which leads to greater inclusive fitness.

Evidence of Inclusive Fitness in Humans:

Human behavior is generally much more complicated than other organisms making it difficult to define human behavior in general organism terms. However, evidence for human altruistic behavior leading to increased inclusive fitness has been observed. While there exists clear evidence towards increased inclusive fitness through altruistic behaviors on behalf of parents and children, much sacrificial behavior by humans is generally done in the hope of reciprocation at some point in the future. Therefore, increasing inclusive fitness in humans is not necessarily dependent upon relatedness. Rather, it is commonly based on reciprocal altruism.

Inclusive Fitness in the Family Structure

Inclusive fitness may also be applied to the familial structure. Parents are frequently self-sacrificing towards their children with the hope that children will carry on the family genes. Frequently, the amount of altruistic behavior displayed by parents to increase their inclusive fitness is related to the amount of parental investment initially involved.


Campbell, N., Reece, J.,et al. 2002. Biology. 6th ed. San Francisco, California. pp. 1145-1148.

Rheingold, Howard, “Technologies of cooperation” in Smart Mobs. Cambridge, MA : Perseus Publishing, 2002 (Ch. 2:pp 29-61)


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