How many species do we share our planet with? It's such a basic and fundamental question to understanding the world around us. It's almost unthinkable that we would not know this number or at least have a good estimate. But the truth is that it's a question that continues to escape the world's taxonomists. An important distinction is how many species we have identified and described and how many species there actually are. We've only identified a small fraction of the world's species, so these numbers are very different. How many species have we described? Before we look at estimates of how many species there are in total, we should first ask the question of how many species we know that we know. Species that we have identified and named. The IUCN Red List tracks the number of described species and updates this figure annually based on the latest work of taxonomists. In 2022, it listed 2.16 million species on the planet. In the chart, we see the breakdown across a range of taxonomic groups — 1.05 million insects, over 11,000 birds, over 11,000 reptiles, and over 6,000 mammals.

species, in biology, classification comprising related organisms that share common characteristics and are capable of interbreeding. This biological species concept is widely used in biology and related fields of study. There are more than 20 other different species concepts, however. Some examples include the ecological species concept, which describes a species as a group of organisms framed by the resources they depend on (in other words, their ecological niche), and the genetic species concept, which considers all organisms capable of inheriting traits from one another within a common gene pool and the amount of genetic difference between populations of that species. Like the biological species concept, the genetic species concept considers which individuals are capable of interbreeding, as well as the amount of genetic difference between populations of that species, but it may also be used to estimate when the species originated.