For several decades now, biologists have been puzzling over sex. In some ways, it seems like a huge waste of effort.

Sexual reproduction requires splitting a species into two sexes, only one of which will be able to produce offspring. There are some species of animals that do without males; the females simply trigger their eggs to develop into embryos without any need for sperm. All the offspring of an asexual animal can produce offspring of their own, instead of just half. So it would make sense that genes that gave rise to asexual reproduction would win out in the evolutionary race.

Clearly that hasn’t happened. The world is rife with sex. Animals do it. Plants do it. Even mushrooms do it.