Identity is such a crucial affair that one shouldn't rush into it.

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.

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.

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.

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.

What do we measure when we measure time? The gloomy answer from Hawking, one of our most implacably cheerful scientists, is that we measure entropy. We measure changes and those changes are all for the worse. We measure increasing disorder. Life is hard, says science, and constancy is the greatest of miracles.

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