View full lesson: http://ed.ted.com/lessons/from-the-top-of-the-food-chain-down-rewilding-our-world-george-monbiot

Our planet was once populated by megafauna, big top-of-the-food-chain predators that played their part in balancing our ecosystems. When those megafauna disappear, the result is a "trophic cascade," where every part of the ecosystem reacts to the loss. How can we stay in balance? George Monbiot suggests rewilding: putting wolves, lions and other predators back on top -- with surprising results.

Lesson by George Monbiot, animation by Avi Ofer.