How Many Species Are There?

by Patrick Appel

The Economist summarizes a new paper on the question:

A paper just published in PLoS Biology uses a novel statistical approach to arrive at a figure of around 8.7m distinct species. But there are some important caveats: it counts only the eukaryotes, that is, critters with relatively complex cells. That means leaving out the bacteria, which are ubiquitous but for which the concept of 'species' is rather problematic, and the archaea, the third great class of Earthly life. So the number arrived at by the researchers almost certainly underestimates the planet's true biological diversity.