The Red Queen hypothesis of why we need sex. Susceptibility to disease typically has a genetic component. Since asexuals keep almost the same genes from 1 generation to the next, parasites can easily evolve to infiltrate their defenses, annihilating clones. In contrast, sex, by mixing up genes, prevents parasites from becoming too well adapted to their hosts. Sex is an advantage because it breaks up gene combinations, creating a genetic version of a moving target.