Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

If local competition for sexual partners occurs amongst siblings, i.e. if brothers reproduce almost exclusively with sisters, it is most advantageous for a female if all the progeny except one are of female sex.From the viewpoint of each offspring, to be more exact, from the viewpoint of the genes on its chromosomes, it is, however, most advantageous if it is a member of the rarer sex, in this case males.A male can locally fertilize all his sisters and leave the greatest number of progeny.Thus, if a mutated gene is capable of converting a female into a male, it will rapidly spread in the population even at the cost of reducing the inclusive fitness of the females.A similar conflict of interests of the genes on the chromosomes of females and genes on the chromosomes of the young in relation to the sex of individuals also takes place in other situations (Eshel & Sansone 1991).It is quite possible that these conflicts and the ensuing battle of the genes for the sex of individuals are the cause of the rapid evolution of the chromosomal mechanism of sex determination (Beukeboom, de Jong, & Pen 2001).These systems are evolutionarily very flexible and frequently even relatively closely related species have quite different systems of genetic determination of sex.