Hermaphrodites

The evolution of anisogamy (sperm and eggs) does not necessarily lead to two classes of individuals that produce either one or the other gamete type (males and females). In diverse taxa, the two sex functions are often combined within the same individual, either sequentially or simultaneously. This hermaphroditism has important consequences for the evolutionary biology of sex, including that (1) sex allocation becomes an individual optimization problem of balancing resource investment into male and female reproduction, (2) sexual selection acts on – and sexual conflict occurs between – sperm donors and sperm recipients, and (3) it opens up the possibility of self-fertilization.