2 March 2007
David Haig
Department of Organismic and Evolutionary Biology
Harvard University
An individual's relatives can be classified as symmetric kin (with equal probabilities of carrying copies of the individual's maternally and paternally derived genes) and asymmetric kin (with unequal probabilities). Inclusive fitness theory has traditionally dealt with the problem of asymmetric kin by employing a coefficient of average relatedness (on the implicit assumption that maternally and paternally derived alleles are constrained to have the same effects). However, if this assumption is relaxed, asymmetries of kinship create the possibility of internal conflicts within individuals over the performance of social behaviors (broadly defined). Conflicts arise because behaviors that increase an individual's matrilineal inclusive fitness may differ from behaviors that increase an individual's patrilineal inclusive fitness. Such conflicts provide a plausible explanation for the evolution of genomic imprinting (gene expression that differs when a gene is maternally and paternally derived). Two factors that can give rise to the kinds of relatedness asymmetries that favor genomic imprinting are multiple paternity of a female's offspring, which favors paternally expressed genes in fetuses that extract more resources from mothers, and sex-biased dispersal, which causes group members to have different degrees of matrilineal and patrilineal kinship and may result in an internal conflict over the relative benefits of selfish and altruistic acts.
A. Varrault et al, "Zac1 regulates an imprinted gene network critically involved in the control of embryonic growth", Developmental Cell 11:711-22 2006. PubMed