Biodiversity is the diversity of genes, species and ecosystems of a region or worldwide. The degree of biodiversity is distributed very unevenly, varying greatly according to latitude and climate, with most of it concentrated in a few biodiversity hotspots. The greatest diversity on land is in tropical forests, which cover less than ten percent of the earth's surface but contain roughly ninety percent of all species. Marine biodiversity is usually greater in the middle latitudes in all oceans, where sea surface temperatures are the highest, and particularly large in coastal areas in the western Pacific Ocean.
The earth's biodiversity has been decreasing rapidly during the past several centuries, with the extinction of ever-increasing numbers of species. This is a result of the relentless destruction of habitats, ever-growing levels of water and land pollution, and a continuous increase in poaching. Moreover, because of the high degree of interdependence among species, each time one species is lost it can endanger, or lead to the extinction of, multiple additional species.
Biodiversity, including the existence of countless varieties of small and microscopic organisms that we cannot see or whose appearance we might not like, is essential for supporting life, including that of humans. For example, birds along with bees and other insects are estimated to be responsible for a third of the world’s crop pollination, and a wide variety of invertebrates and microorganisms help maintain the productivity of the soil. Likewise, complex webs of organisms in the oceans and other water bodies are necessary to sustain the seafood that provides many millions of people with their main source of protein.
Numerous medicines, along with many other complex chemicals, originate from plants and animals. For example, nearly 25 percent of the pharmaceuticals used in modern medicine are obtained from tropical plants, and the majority of cancer drugs are natural or synthetic products derived from or inspired by living organisms. Thus, every time another species becomes extinct, the opportunity for discovery of a new medicine or other useful substance is lost forever.