Animals are going extinct at a rate 1,000 times faster than they did 60 million years ago, largely in part thanks to humanity's global spread. A team of American and Swiss evolutionary biologists analyzed the current and prehistoric diversification rates - that is, the number of new species arising minus the number of species dying off - by molecular comparisons of plant and animal family trees.
Today, extinction claims 100 species out of every million per year, roughly speaking. Scientists knew the rate was much slower millions of years ago, but this study suggests it was even lower than previously thought - only one out of every 10 million species per decade (that's 0.1 out of a million annually).
"We've known for 20 years that current rates of species extinctions are exceptionally high," states Stuart Pimm, president of the conservation group SavingSpecies and a co-author of the report. "This new study comes up with a better estimate of the normal background rate - how fast species would go extinct were it not for human actions. It's lower than we thought, meaning that the current extinction crisis is much worse by comparison."
Unfortunately, the best evidence shows that extinction rates will worsen over the next century. As Elizabeth Kolbert, author of the book The Sixth Extinction, tells National Geographic:
We're not just warming the world, we're cutting down the rain forest. We're not just cutting down the rain forest, we're moving invasive species into the rain forest. So you just add these all up, and you say, that's a lot, and that's how you get to saying: We are the asteroid now.
The new report in the journal Conservation Biology "reinforces the urgency to conserve what is left and to try to reduce our impacts," says study author Jurriaan de Vos, a Brown University ecologist. "It was very, very different before humans entered the scene."