[Theory is] an explanation that has been confirmed to such a degree, by observation and experiment, that knowledgeable experts accept it as fact. That's what scientists mean when they talk about a theory: not a dreamy and unreliable speculation, but an explanatory statement that fits the evidence. They embrace such an explanation confidently but provisionally - taking it as their best available view of reality, at least unil some severely conflicting data or some better explanation might come along.

To drown a river beneath its own impounded water, by damming, is to kill what it was and to settle for something else. When the damming happens without good reason . . . then it's a tragedy of diminishment for the whole planet, a loss of one more wild thing, leaving Earth just a little flatter and tamer and simpler and uglier than before.

Kill off the sacred bear. Kill off the ancestral crocodile. Kill off the myth-wrapped tiger. Kill off the lion. You haven't conquered a people, or their place, until you've exterminated their resident monsters.

The elk are the most abundant large herbivores in the Yellowstone ecosystem. There are thousands and thousands of them. They migrate in and out. And those migration routes need to stay open.

Among the earliest forms of human self-awareness was the awareness of being meat.

And so in 1975, the grizzly bear was put on, as I said - on the endangered species list as threatened. And new measures were taken, for instance, bear-proofing garbage, creating new regulations to - essentially to try and keep people and people's food away from the bears, let the bears adjust to eating the abundant wild food that's available in Yellowstone and allow them to be more wild, to be independent of humans as sources of foods for the good of both sides. And that has been quite successful.

You can hike into the Yellowstone backcountry. You can camp in the Yellowstone backcountry. You can take food into the Yellowstone backcountry, and you're surrounded by grizzly bears. And it's - it's a very, very thrilling, peculiar situation. Every sound that you hear in the night, you wonder is this a grizzly bear coming to tear into my tent?