Hamilton’s rule, and the model of kin selection on which it is based, was derived in the 1960s, when there was great emphasis on the individual, and on the gene, as the unit of selection. The concept of inclusive fitness encapsulated the notion that a gene that lowered the fitness of its bearer could promote behaviors that increased the fitness of consanguineous relatives, therefore increasing the frequency of the gene. Therefore it was the inclusive fitness of the gene that was assumed to predict the evolutionary increase or decrease of that gene. The extension of this concept into more teleological parlance became the selfish gene hypothesis. Hamilton’s model of kin selection has had a great influence on biology, anthropology, economics, and other fields. My results indicate, however, that although kin selection may occur, Hamilton’s rule is invalid.Human Biology
Volume 77, Number 4, August 2005
Kin Selection in Human Populations: Theory Reconsidered
B. J. Williams
Past considerations of kin selection have assumed a dyadic fitness exchange relationship between altruist and recipient. This approach does not account for all alleles affected by altruistic behavior. This can be corrected by focusing on matings rather than on individuals. I present a model that tries to account for fitness changes resulting from altruistic acts, not only for the altruist and recipient but also for their spouses, in an evolving population. Results from this model indicate that Hamilton's rule fails to predict when the altruism allele will increase in frequency and, more important, suggest that kin selection can, at most, account for low levels of a gene for altruism but only if fairly extreme conditions are met.