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.

As I started to read nonfiction in the mid '70s, I discovered, holy cow, there was a lot of imaginative nonfiction. Not the kind where people use composite characters and invented quotes. I hate that kind of nonfiction. But imaginative in the sense that good writing and unexpected structure and vivid reporting could be combined with presenting facts.

Evolution as described by Charles Darwin is an scientific theory, abundantly reconfirmed, explaining physical phenomena by physical causes. Intelligent Design is a faith-based initiative in rhetorical argument. Should we teach I.D. in America's public schools? Yes, let's do - not as science, but alongside other spiritual beliefs, such as Islam, Zoroastrianism and the Hindu Idea that Earth rests on Chukwa, the giant turtle.

I wrote four novels, but then I realized that the world didn't need me to be a novelist, but the world could use me as a nonfiction writer.

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?

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.

There was a very important superintendent of Yellowstone, a man who was involved in the founding of the National Park Service itself, Horace Albright. And he became superintendent, which is the boss of Yellowstone Park, in 1919 - from 1919 to 1929. Later, he was director of the park service itself. Albright embraced the idea that in order for the national parks - and Yellowstone in particular - to have support from the American people and from politicians, there needed to be wildlife as spectacle.