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E. New Insight into a Lethal Cancer

Narrator: This is Science Today. Between 10 thousand and 50 thousand years ago, about two-thirds of the planet's megafauna, or large animals, went extinct. These animals included mammoths, mastodons and saber-toothed cats. Tony Barnosky, a professor of Integrative Biology at the University of California, Berkeley, says during this time period, the climate changed dramatically going from the last Ice Age into our present interglacial.

Barnosky: That also happens to be a time when humans first arrived in various parts of the world, or increased their populations sizes in various parts of the world. 106 So there's this coincidence that the two possible causes and it's been quite a polarized argument as to whether it was all humans versus all climate or something in between.

Narrator: Barnosky says it was something in between and it could happen again.

Barnosky: We once again are seeing this ramping up of human population pressure with unprecedented climate change.

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