Biodiversity is the variety of all living things on Earth, from the genes inside a single organism to the range of species in a forest to entire ecosystems like coral reefs and grasslands. It operates on three interconnected levels: genetic diversity (the variation in DNA within a species), species diversity (the number of different species in an area), and ecosystem diversity (the variety of habitats and ecological communities across a landscape). These three levels work together to keep the natural world functioning, and by extension, to keep human civilization running.
The Three Levels of Biodiversity
Genetic diversity is the most granular level. Within any single species, individuals carry slightly different versions of genes. This variation is what allows populations to adapt when conditions change. A wheat field planted with genetically identical crops, for example, can be wiped out by a single disease. But a field with genetic variation will likely contain some plants that resist the pathogen. Wild relatives of domesticated crops are especially rich in these protective traits. Wild wheat ancestors carry genes for broad fungal resistance, and wild potato relatives contribute resistance to blight. These genetic reservoirs are irreplaceable raw material for adapting agriculture to new diseases and shifting climates.
Species diversity is what most people picture when they hear “biodiversity”: the sheer number of different plants, animals, fungi, and microorganisms sharing a habitat. A tropical rainforest with 500 tree species is more species-diverse than a northern pine forest with 10. But raw count isn’t the whole picture. Scientists also measure evenness, which captures how evenly individuals are distributed among those species. A forest with 100 species where one species makes up 95% of all trees is functionally less diverse than a forest with 50 species split more equally.
Ecosystem diversity is the broadest scale. It describes the range of different habitats, biological communities, and ecological processes within a region. A country that contains mangrove swamps, alpine meadows, desert, and temperate forest has high ecosystem diversity. Each of these systems supports unique species and performs different functions, from filtering water to storing carbon to buffering coastlines against storms.
Why Biodiversity Matters for Daily Life
The practical value of biodiversity is enormous, and most of it is invisible. Insects pollinate roughly three-quarters of the world’s food crops. Wetlands filter drinking water. Forests absorb carbon dioxide and release oxygen. Soil organisms break down waste and cycle nutrients that grow food. A landmark economic analysis estimated that the world’s ecosystems collectively produce around $33 trillion worth of these services every year. For perspective, global economic output at the time of that study was about $18 trillion. Nature’s contributions dwarf what human economies generate on their own.
Food security depends directly on genetic diversity within crops and their wild relatives. Modern agriculture relies heavily on a small number of staple crops, which makes the global food supply vulnerable. When a new pest or disease emerges, plant breeders turn to wild and traditional varieties to find resistance genes they can breed into commercial lines. Landraces (locally adapted traditional crop varieties) harbor genetic adaptations to regional stresses built up over centuries of cultivation. Losing those varieties means losing options for the future.
How Scientists Measure It
Counting biodiversity isn’t as simple as tallying species. Researchers use several complementary metrics. Species richness is the most straightforward: the number of distinct species found in a given sample or area. Evenness measures how balanced the population sizes are across those species. The Shannon-Wiener index combines both richness and evenness into a single number, making it one of the most widely used tools for comparing biodiversity across sites or tracking changes over time. A higher Shannon-Wiener value means a community is both rich in species and relatively balanced in their abundance.
At larger scales, scientists track trends using tools like the Living Planet Index, which monitors tens of thousands of wildlife populations worldwide to estimate how vertebrate numbers are changing over time.
The Current State of Global Biodiversity
The numbers are stark. Monitored wildlife populations have declined by an average of 73% between 1970 and 2020, according to the most recent Living Planet Index based on the largest dataset ever assembled. Freshwater species have been hit hardest, with an 85% decline over the same period. Latin America and the Caribbean saw a 95% drop, and Africa experienced a 76% decline.
The rate at which species are disappearing is also far above normal. The natural “background” rate of extinction, the pace at which species would vanish without human influence, is roughly 2 species lost per 10,000 species per century for mammals. Current vertebrate extinction rates are up to 100 times higher than that baseline. Species losses that would naturally take 800 to 10,000 years have been compressed into the last century alone. Researchers have described this acceleration as the beginning of a sixth mass extinction event in Earth’s history.
Biodiversity loss is now considered a breached planetary boundary. Scientists have identified nine critical Earth system processes that, if kept within safe limits, would maintain the stable conditions human civilization developed under over the past 10,000 years. Biosphere integrity is one of those nine boundaries, and humanity has pushed past it. Six of the nine boundaries total have now been crossed, meaning the planet is operating outside the environmental conditions that supported the rise of agriculture, cities, and modern societies.
Biodiversity Hotspots
Not all regions carry equal weight for conservation. Scientists have identified 36 biodiversity hotspots around the world, areas where protecting species yields outsized results for global biodiversity. To qualify, a region must meet two criteria: it must contain at least 1,500 plant species found nowhere else on Earth, and it must have lost 70% or more of its original natural vegetation. In other words, hotspots are both irreplaceable and under severe threat. These 36 regions are where conservation investments can prevent the most extinctions per dollar spent.
Global Policy Response
The most significant international agreement on biodiversity is the Kunming-Montreal Global Biodiversity Framework, adopted in 2022. It sets 23 action-oriented targets for 2030. The headline commitment, known as “30 by 30,” calls on nations to effectively conserve and manage at least 30% of the world’s land, inland waters, and ocean areas by the end of the decade. The framework specifically targets areas of particular importance for biodiversity and ecosystem services, and it requires that these protected zones be ecologically representative, well-connected, and equitably governed. It also explicitly recognizes the rights and territories of Indigenous peoples and local communities, whose land stewardship has historically maintained some of the most biodiverse regions on the planet.