Extinction happens to be a perfectly natural process, but only when it is in sync with evolution of new species. However, the rate at which extinction of species is occurring over the last 400 years - with a steep rise over the last hundred years or so, is something that has left the environmentalists bewildered. It doesn't end there, as the number of species which are threatened with extinction i.e. the species which are vulnerable, endangered and critically endangered, is also very high.