trong>Narrator: This is Science Today. The extinction of Earth's large mammals during the late Pleistocene – about 50 thousand and 10 thousand years ago – could happen again within the next one hundred years. Tony Barnosky, a professor of integrative biology at the University of California, Berkeley, says just as in the Pleistocene, the cause of this extinction may be a combination of climate change and increased human population sizes.

Barnosky: The reason that's relevant now is because we're entering into a phase where we have got the same two things acting in a much more scaled up way.

Narrator: For years there has been a very polarized debate between those who favor humans as the main cause of the extinctions versus those who blame climate change. In a recent review, Barnosky concluded it was both.

Barnosky: I think what's significant about this study is it shows that really in some places, we can pretty clearly document that it was climate change. In other places, we can pretty clearly document that climate probably wasn't so important – that it was human population pressure.

Narrator: For Science Today, I'm Larissa Branin.