The past and future of known biodiversity: Rates, patterns, and projections of new species over time.

Our understanding of biodiversity patterns comes primarily from described species. Here, we analyze how known biodiversity has increased across living organisms. Past research suggested that the number of new species per year peaked near 1900 and that only ~2 million species exist. We find that overall rates of species descriptions have recently accelerated, with the largest numbers of new species per year all in the past ~20 years (2000 to 2020). The largest groups grew the most quickly during this period, including animals, arthropods, insects, and beetles. However, long-term trends in rates of species descriptions were often unrelated to recent rates and current richness. For example, rates for fungi have recently increased, whereas rates for insects have not. Extrapolating these rates of species descriptions into the future requires considerable caution. Nevertheless, some intriguing patterns are suggested, such as unexpectedly high projected species numbers of plants, fungi, arachnids, malacostracan crustaceans, ray-finned fishes, and amphibians.