Applying the same statistical approach to extinction data revealed a rate of 100 to 1,000 species lost per million per year, mostly due to human-caused habitat destruction and climate change. (See: "7 Species Hit Hard by Climate Change—Including One That's Already Extinct.")
To calculate the rate of extinction before modern humans evolved, about 200,000 years ago, Pimm and his colleagues reviewed data from fossil records and noted when species disappeared, then used statistical modeling to fill in holes in the record. That analysis revealed that before humans evolved, less than a single species per million went extinct annually.