Importance of Background Extinction

There are two basic kind of extinctions – background extinctions and mass extinctions. During a background extinction, the disappearance of species takes place rarely, even more rarely than speciation, and occurs at a background extinction rate. There is a complex calculation that determines a background rate of extinction for an animal. Currently there are about 5,500 species of mammals. The background extinction rate is at .25 per million species per year. At that rate, one mammal will go extinct every seven hundred years.