John Launer in Literary Hub:
Why do males exist? If you learned biology at school, your teachers will probably have told you it was because combining genes from different individuals—one male and one female—increases variation in a species, and it is variation that helps a species survive.
Unfortunately, most evolutionary experts stopped believing in this explanation over 30 years ago. From a reproductive point of view, no individual is interested in anything very much beyond donating genes to the next generation. As far as whole species are concerned, they are preserved or wiped out more or less at random, largely according to the whims of climate and geology. In addition, you don’t actually need sexes to produce variation: the vast majority of organisms like microbes happily mutate and vary withoutsex.
The great evolutionist John Maynard Smith regarded sex as more or less inexplicable. He talked of “the twofold cost of males.” First, it is incomprehensible that any female should want to throw away half her genes and take on someone else’s, when theoretically she could just produce clones of herself instead. Secondly, the males of many species are entirely useless at doing anything except sitting around, getting fat at the females’ expense, and—in the words of Richard Dawkins—duffing up other males. Among some animals, such as elephant seals, the vast majority of males die as wasteful, disappointed virgins.
Given this wastefulness, it is perhaps not surprising that there are at least 40 species where the female kills the male during or after sex.