Today the majority of the world's environments are changing faster than the ability of most species to adapt to such changes through natural selection. The primary cause is the destruction of habitat, drainage of wetlands, conversion of shrub lands to grazing lands, cutting and clearing of forests and urbanization and suburbanization. Commercial exploitation and overhunting of animals for food and other products has also caused many species to become extinct or endangered. The slaughter of animals for oil, meat, horns, ivory, skin and fur has brought many animals to the brink of extinction. The introduction of new diseases, parasites, and predators which native species have no defence for have also greatly reduced some species.
Pollution is another important cause of extinctions.
Toxic chemicals have become concentrated in food webs, affecting most strongly thoses species at the end of the chain.