"Sex’s history, its forms, and its uses all turn out to be far stranger and more various than biologists had imagined...." (opens in new tab)

"Lixing Sun... a biologist at Central Washington University, begins his story with a protozoan called Tetrahymena thermophila. T. thermophila are tiny—just a twentieth of a millimetre long—yet can reproduce two different ways: by splitting themselves in half or, when they’re starving, by engaging in a kind of proto-sex called conjugation, in which two cells briefly fuse and swap genetic material. The protozoa come in seven distinct 'mating types,' which means that there are twenty-one possibl...