Coadaptation and conflict, misconception and muddle, in the evolution of genomic imprinting.

Common misconceptions of the 'parental conflict' theory of genomic imprinting are addressed. Contrary to widespread belief, the theory defines conditions for cooperation as well as conflict in mother-offspring relations. Moreover, conflict between genes of maternal and paternal origin is not the same as conflict between mothers and fathers. In theory, imprinting can evolve either because genes of maternal and paternal origin have divergent interests or because offspring benefit from a phenotypic match, or mismatch, to one or other parent. The latter class of models usually require maintenance of polymorphism at imprinted loci for the maintenance of imprinted expression. The conflict hypothesis does not require maintenance of polymorphism and is therefore a more plausible explanation of evolutionarily conserved imprinting.