Is sex maintained to facilitate or minimise mutational advance?

Abstract

There are two alternative hypotheses for the selective advantages of sex: (i) The "Fisher-Muller" model: sex facilitates evolutionary adaptation to changing environments. (ii) The "Ratchet" model: sex minimises the mutational load. The relative importance of these hypotheses is discussed with reference to (a) comparative data on sexual and asexual reproduction, (b) the timing of sex in species with asexual/sexual alternation, (c) the advantages of haploid/diploid alternation, (d) the disadvantage associated with the recombinational load. It is concluded that the Ratchet model may well be the major mechanism which maintains sex.