Selfish genetic elements and their role in evolution: the evolution of sex and some of what that entails.

An individual is often considered (sometimes implicitly) to be the product of a well functioning mutualism between its constituent genes. This however need not be so. One consequence of sexual reproduction is that costly competition within an individual between genes that are effectively allelic can provide the conditions for the spread of suppressors of such competition. The spread of both these ultracompetitive alleles (alias selfish genetic elements) and their suppressors is evidence of a 'conflict of interests' within the genome. That this conflict is a potentially important force in the evolution of genetic systems is illustrated by consideration of the problem of the evolution of sexes (alias mating types). One hypothesis holds that sexes are the result of selection on nuclear genes to coordinate the inheritance of cytoplasmic genomes (usually this means the enforcement of uniparental inheritance) so as to prevent competition between unrelated cytoplasmic genomes. This hypothesis is tested against five comparative predictions and shown to receive considerable empirical support.