Naturalists have been trying for centuries to catalogue all of the species on Earth, and the effort remains one of the great unfinished jobs in science. So far, researchers have named about 2.3 million species, but there are millions – perhaps even billions – left to be discovered.

As if this quest isn’t hard enough, biologists cannot agree on what a species is. A 2021 survey found that practising biologists used 16 different approaches to categorising species. Any two of the scientists picked at random were overwhelmingly likely to use different ones.