Earth is home to an astonishing variety of life, from the smallest microorganisms to the largest whales. Understanding this immense biodiversity begins with a fundamental question: how many species inhabit our planet? While scientists have made significant progress in cataloging life forms, the exact number remains a subject of ongoing discovery and estimation. The vastness of Earth’s ecosystems and the sheer diversity of organisms present considerable challenges in achieving a definitive count.
The Current Count of Described Species
Scientists have formally identified and described approximately 2.16 million species globally as of 2022. This figure is continuously updated as new species are discovered and documented by taxonomists. Among the major taxonomic groups, insects represent the largest proportion of described animal species, with around 1 million identified, over half of all described eukaryotic species.
Plants also contribute significantly, with approximately 391,000 vascular plant species identified, including about 369,000 flowering plants. Fungi have about 120,000 to 155,000 described species, though this is a small fraction of their total diversity. In marine environments, roughly 242,000 species have been documented. Vertebrates, including mammals, birds, amphibians, reptiles, and fish, comprise a smaller but well-studied group, with around 65,000 described species.
Why the Number is Approximate
The count of described species is an approximation due to the complexities of taxonomy, the science of classifying organisms. One challenge arises from ongoing reclassification, where scientific understanding evolves, leading to changes in how species are grouped. For instance, a single species might be split into several distinct ones upon further study.
Another factor is synonymy, occurring when the same species is inadvertently described and named multiple times by different researchers. This duplication necessitates careful review and correction, reducing the official count of unique species. Cryptic species, morphologically similar but genetically distinct, also complicate identification, appearing identical but being separate evolutionary lineages. The immense scale of the task and a global shortage of taxonomists further contribute to the approximate nature of the count.
Estimating Earth’s Total Species
Beyond the species already described, a much larger number of organisms remain undiscovered. Estimates for Earth’s total species diversity vary widely, ranging from a few million to potentially trillions, especially considering microorganisms. A widely cited estimate suggests around 8.7 million eukaryotic species, with approximately 6.5 million on land and 2.2 million in the oceans. This implies a substantial majority of species, particularly in marine environments, have yet to be formally described.
Scientists employ various methods to arrive at these estimations. One approach extrapolates from known biodiversity in well-studied areas or taxonomic groups to less explored ones, like the deep sea or soil microbes. Species-accumulation curves, which plot the number of new species found against increased sampling effort, can also indicate when a significant portion of species in an area has been identified, allowing for an estimation of the remaining unknown species. Expert opinion, based on extensive knowledge of specific groups and regions, also contributes to these figures. However, these methods come with uncertainties due to the difficulty of sampling certain environments and the sheer diversity of life forms.
The Importance of Species Identification
Identifying and describing species is foundational for understanding the planet’s biodiversity. This work provides the knowledge necessary to comprehend how life is organized and interconnected within ecosystems. Accurate species identification is also crucial for effective conservation efforts, allowing scientists to identify species at risk of extinction and prioritize strategies.
Beyond conservation, knowing what species exist supports drug discovery, as many medicines are derived from natural compounds found in various organisms. Understanding species roles also contributes to assessing ecosystem health, monitoring invasive species, and ensuring the overall stability of Earth’s natural systems. This fundamental scientific pursuit informs our ability to manage natural resources and respond to environmental changes.