Why Is It So Hard to Define a Species?
An editorially independent publication supported by the Simons Foundation.
The “species” category is almost certainly the best known of all the taxonomic classifications that biologists use to organize life’s vast diversity. It’s a linchpin of both conservation policy and evolutionary theory, though in practice biologists have struggled to find a definition that works across the natural world. In this episode, Kevin de Queiroz, a zoologist and evolutionary biologist, talks with host Janna Levin about the variety of ways to conceive of a species, and ways to understand the relationships among living things.
JANNA LEVIN: If you were to look around and start counting all the organisms in your line of sight — flora and fauna, single-celled and multicelled, macroscopic and microscopic — the task would far exceed a human lifetime. A single acre may hold hundreds of millions of individual organisms. So it’s next to impossible to say precisely how many co-inhabitants we have here on Earth.
Perhaps in an effort to determine how we fit into the mix, we’ve spent hundreds of years attempting to categorize the living things around us, grouping them by shared traits into a series of taxonomic ranks — of which the most specific, and likely most familiar, is species.
