Extinction is a natural feature of evolution because for some species to succeed, others must fail. Since life began, about 99 percent of the earth's species have disappeared and, on at least five occasions, huge numbers have died out in a relatively short time. The most recent of these mass extinctions, about 65 million years ago, swept away the dinosaurs and many other forms of life. However, despite such catastrophes, the total number of living species has, until recently, followed a generally upward trend.

Today, the extinction rate is increasing rapidly as a result of human interference in natural ecosystems. Primates, tropical birds, and many amphibians are particularly threatened. For the foreseeable future, this decline is set to continue because evolution generates new species far more slowly than the current rate of extinction. A new and current mass extinction commonly referred as The Sixth Extinction.