George Monbiot calls it one of "the most exciting scientific findings in the past half century." That's a lofty statement, but one that he's willing to back up. The scientific finding that Monbiot is referring to is a 'trophic cascade,' in which the reintroduction (or removal) of the top predator of an ecosystem drastically changes said ecosystem in numerous ways. In 1995, wolves were reintroduced into Yellowstone National Park after having been absent for several decades. As a result, an incredible change was now underway.

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With wolves back on the scene, the deer population reduced. Not only that, but the deer's behavior changed as well. They avoided certain areas where they were most vulnerable, which in turn gave life back to the vegetation in those areas. Then came the birds, and the beavers. The beavers built dams which provided a habitat for a number of other species. Just like that, the ecosystem was changing. The river changed as well; there was less erosion and more ripple sections.

 Below, you can hear Monbiot reiterate why this trophic cascade is so fascinating.