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

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.

By the cold Darwinian logic of natural selection, evolution codifies happenstance into strategy.

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.

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.

[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.

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.