Two Sexes is Inefficient

Many fungi are sexual, but they do not have males. They have tens of thousands of different sexes, all physically identical, all capable of mating on equal terms. but all incapable of mating with themselves. Even among animals there are many, such as the earthworm, that are hermaphrodites. To 3e sexual does not necessarily imply the need for sexes, let alone for just two sexes, let alone for two sexes as different as men and women. Indeed, at first sight, the most foolish system of all is two...