Biodiversity is the total variety of life on Earth, spanning every level of biological organization: the genetic differences within a single species, the range of species in a given habitat, and the variety of ecosystems across the planet. It covers everything from the bacteria in a handful of soil to the complex web of life in a tropical rainforest. Scientists estimate roughly 8.75 million species exist on Earth, yet only about 1.2 million have been formally described, meaning the vast majority of life remains undiscovered.
The Three Levels of Biodiversity
Biodiversity operates on three distinct scales, each one essential to the health of the whole system.
Genetic diversity refers to the variation in DNA within a single species. A wild grain with dozens of genetic variants is more likely to survive a new disease than a monoculture crop where every plant is genetically identical. This genetic pool is what allows breeders to develop more resilient food crops, livestock, and marine species over time.
Species diversity is the one most people picture: the number and variety of different species in a region. A coral reef teeming with thousands of fish, invertebrate, and plant species has high species diversity. A commercial pine plantation has very low species diversity. The range of estimates for total species on Earth is staggeringly wide, from 2 million to as high as 3 trillion depending on whether microorganisms are included. One widely cited projection puts the number at about 8.75 million, including roughly 7.8 million animals, 298,000 plants, and 611,000 fungi.
Ecosystem diversity captures the variety of habitats, biological communities, and ecological processes across a landscape. Wetlands, grasslands, deep-sea vents, and mangrove forests each support different communities of life and function in different ways. Forests alone store 80% of land-based biodiversity and absorb roughly 2.6 billion tonnes of carbon dioxide every year.
Why Biodiversity Matters to People
The practical benefits that ecosystems provide to human life are often grouped into four categories. Provisioning services include the tangible outputs: food, freshwater, timber, fiber. Healthy ecosystems supply 75% of global freshwater resources, with wetlands playing a central role in water purification. Regulating services cover the behind-the-scenes work of nature: pollination, flood control, carbon storage, disease regulation. Supporting services maintain the foundation, things like soil formation, nutrient cycling, and habitat for wildlife. Cultural services are the non-material benefits: recreation, tourism, spiritual connection, artistic inspiration.
Economists have attempted to put a price tag on all of this. One landmark analysis estimated that the world’s ecosystems collectively produce an average of $33 trillion in services every year, a figure that dwarfs many national economies and underscores how deeply the global economy depends on functioning natural systems.
Biodiversity and Medicine
About 25% of all drugs prescribed worldwide come from plants, with 121 plant-derived compounds in current medical use. Of the 252 drugs the WHO considers basic and essential, 11% are exclusively plant-based, and many others are synthetic versions originally modeled on natural compounds. An estimated 60% of anti-tumor and anti-infectious drugs on the market or in clinical trials trace their origins to natural sources. Every species lost before it is studied is a potential medicine that will never be found.
How Fast Biodiversity Is Declining
Current extinction rates are tens to hundreds of times higher than the natural background rate that prevailed over the past 10 million years. During the 20th century alone, 390 vertebrate species disappeared. Based on the expected background rate for vertebrates (mammals, birds, fish, reptiles, amphibians), only about nine extinctions would have been normal over that same period. That means vertebrates vanished more than 40 times faster than they should have.
Population sizes tell a similar story. The WWF’s 2024 Living Planet Report tracked monitored vertebrate wildlife populations and found an average 73% decline since 1970. That does not mean 73% of individual animals are gone. It means that, on average, the populations being tracked are roughly a quarter the size they were five decades ago. Some regions and species groups have fared far worse.
The Five Main Drivers of Loss
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) ranked the five direct drivers of biodiversity loss by their global impact. In order:
- Changes in land and sea use: Converting forests to farmland, draining wetlands, expanding cities, and trawling ocean floors destroy habitat on a massive scale. This is the single biggest driver.
- Direct exploitation of organisms: Overfishing, hunting, logging, and wildlife trade remove species faster than they can recover.
- Climate change: Shifting temperatures, altered rainfall patterns, and more extreme weather events push species out of habitats they evolved to occupy.
- Pollution: Pesticides, plastics, excess nitrogen from fertilizers, and industrial chemicals degrade ecosystems on land and in water.
- Invasive alien species: Species introduced to new environments, whether deliberately or accidentally, can outcompete, prey on, or bring disease to native wildlife.
Biodiversity Hotspots
Not all regions carry equal biological weight. Conservation scientists use the term “biodiversity hotspot” for areas that meet two strict criteria: the region must contain at least 1,500 species of vascular plants found nowhere else on Earth, and it must have lost 70% or more of its original natural vegetation. In other words, a hotspot is both irreplaceable and threatened. These regions cover a small fraction of the planet’s land surface but hold a disproportionate share of its unique species, making them top priorities for conservation funding and protection.
Global Conservation Targets
In 2022, nearly every country in the world adopted the Kunming-Montreal Global Biodiversity Framework, which set a series of targets for 2030. The most prominent is the “30 by 30” goal: conserve and effectively manage at least 30% of Earth’s land, inland waters, and ocean areas by the end of the decade, with particular focus on areas of high biodiversity importance. A parallel target calls for at least 30% of degraded terrestrial, freshwater, and marine ecosystems to be under active restoration by 2030. Meeting these goals would require a dramatic acceleration from current levels of protected area coverage, along with cooperation with Indigenous peoples and local communities whose traditional territories overlap with many of the most biodiverse places on the planet.