  The two classic theories for the existence of sexual replication are that sex
purges deleterious mutations from a population, and that sex allows a
population to adapt more rapidly to changing environments. These two theories
have often been presented as opposing explanations for the existence of sex.
Here, we develop and analyze evolutionary models based on the asexual and
sexual replication pathways in Saccharomyces cerevisiae (Baker's yeast), and
show that sexual replication can both purge deleterious mutations in a static
environment, as well as lead to faster adaptation in a dynamic environment.
This implies that sex can serve a dual role, which is in sharp contrast to
previous theories.
