Altruism as a Handicap: The Limitations of Kin Selection and Reciprocity

Abstract

The phenomenon of at the nest has exposed ornithologists to the problem of the evolution of altruism, i.e. why should a non-breeder invest in the fitness of breeders rather than trying itself to breed. Until the 1960s was explained by many biologists through models of selection (GS), i.e. the investment of the non-breeders in the breeding of their group members was justified by its contribution to the group. GS was later rejected by most evolutionary biologists (Maynard Smith 1964, Lack 1966, Williams 1966), and another model, that of kin-selection (KS) (Hamilton 1964) was suggested as an alternative solution to the problem of altruism. In KS models the investment of the altruist is justified by the benefit to its relatives. However, the many studies on group living birds which have resulted from the growing interest in the dilemma of altruism, have revealed that the are in fact often not related to the breeders (Ligon and Ligon 1990, Reyer 1990, Zahavi 1990). Trivers (1971) suggested an additional model altruism (RA) to interpret altruistic adaptations among non-relatives. This latter model suggests that the investment of the altruist is compensated by a gain from a reciprocal investment by other group members. However, data from several field studies have indicated that in many cases the act of the non-related altruist was not reciprocated. In these cases neither KS nor RA could explain helping at the nest. It was evident, however, in some of these studies (Ligon and Ligon 1990, Reyer 1990, Zahavi 1990) that many of the were enhancing their own chances to breed. Helping by nonrelated birds, which is not reciprocated, can therefore only be interpreted as a simple selfish investment. However, these findings did not stimulate further research into the possibility that helpers in general gain direct advantages by their apparently altruistic investment.