VI.3.6 Crossing-over may have evolved as a defense against meiotic drive.
Some authors (Ridley 2000)are of the opinion that meiotic drive is an extremely important evolution factor, where the effect of this factor on the average biological fitness of the members of the population is almost always negative. Meiotic drive could be manifested especially strongly in organisms in which crossing-over would not exist and in which alleles would thus not be mixed in pairs of homologous chromosomes. Competition of the individual chromosomes for the most effective spreading in the gene pool of the population through meiotic drive in these cases could generally predominate over competition between the individual alleles for the most effective transfer to further generations through the positive effect on the biological fitness of their bearers, i.e. over natural selection. Crossing-over, which breaks up alliances of alleles of individual chromosomes, is a very effective mechanism limiting the action of meiotic drive, and its development in evolution may even be a necessary condition for the existence of sexual reproduction based on meiosis and syngamy (Haig & Grafen 1991).