Males and the advantage of sex.

Most sexual populations are at a two-fold disadvantage to parthenogenetic populations. This is because males are produced in equal numbers to females and males contribute virtually no food supplies to the zygote. Females therefore "waste their energy" in the production of sons. Parthenogenetic females produce only daughters and therefore have a two-fold advantage. It is argued that female choice (of males) and male: male competition can reduce mutational loads and this may compensate for the two-fold disadvantage of males. The Haldane mutation load principle indicates a load of 2mu, where mu is the mutation rate per gamete. Female choice and male: male competition are capable of reducing this substantially. The effect is greatest with mildly deleterious mutations and is therefore dependent on the fitness of the mutations. This is in contrast to the Haldane principle load which is determined by the mutation rate only. As most mutations appear to be mildly deleterious the load in many sexual populations may be substantially below that indicated by the Haldane principle.