PATHOGEN RESISTANCE AS THE ORIGIN OF KIN ALTRUISM

It is suggested that pathogen and parasite avoidance act as a driving force for kin selection. Preferential association with relatives decre ases the probability of infection with unfamiliar pathogens. Altruisti c behavior towards kin will further decrease the danger of infection b y increasing the representation of relatives in a group. Such a behavi oral strategy could evolve if pathogen resistance were heritable. High ly polymorphic major histocompatibility (MHC) genes largely determine heritable resistance to particular pathogens. The degree of relatednes s within a group correlates with the degree of similarity in MHCs. It has been shown that detection of MHC type by mice guides preferential kin association. Pathogen avoidance appears to be the simplest explana tion for the existence of a direct link between detecting the heritabl e component of the immune system and kin altruism. Detection of MHC al so serves kin avoidance in mating. Periodic introduction of new genes including MHCs through mating provides resistance to the unavoidable a ppearance of foreign virulent pathogens (Hamilton et al., 1990, Proc. Natl Acad. Sci. U.S.A. 87, 3566-3573). It is suggested that kin prefer ence favoring homogeneity punctuated by introduction of new genes thro ugh mating provides an optimal strategy for pathogen avoidance. Aggres sion might also serve to decrease infection by isolating or eliminatin g individuals with unrelated MHCs. (C) 1998 Academic Press