Population Viscosity and Kin Selection

Abstract

Kin selection may be broken down into two components: intrafamily and interfamily selection. When an altruism coding allele is rare (i.e., at its emergence) within the family the frequency of the altruism coding genotype necessarily declines; it is only by differential production of reproductives between families that kin selection can act to increase the frequency of this genotype in the population. Thus kin selection acts on a partitioned population: families with altruists disperse more offspring than families without altruists. This has implications for current theories on the evolution of eusociality, especially with respect to the role of population viscosity. In an environment with limited resources, population viscosity, by preventing offspring dispersal, creates a population structure where, locally, the proportion of altruism coded genotypes is declining. If the population is at carrying capacity, and if survivorship is unrelated to altruistic genotype, over generations fewer of this genotype survive to reproduce. In effect, continual population viscosity disrupts kin selection. This suggests that theories which invoke population viscosity to provide high values of r are wanting. In particular, contrary to the polygynous family hypothesis (see text), kin selection in the presence of population viscosity cannot yield evolutionarily stable semisociality. Rather, effective kin selection requires parental mediation to form temporary groups of related conspecifics. Thus explanations invoking kin selection must ultimately focus on the parent.