why males? why do so many complex organisms have a whole sex which does not bear offspring? One hypothesis is that males are good for purging genetic load via sexual selection. On a genetic level all individuals carry deleterious mutations, which they pass on to their offspring. But, because of sample variance in transmission, there will be a distribution of outcomes in any given set of offspring. By chance some individuals will exhibit a higher load of deleterious alleles, while others will carry fewer alleles. If this load is correlated to traits which are visible to the opposite sex, then excess load every generation can be purged through reproductive skew