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.

Mathematics to me is like a language I don’t speak though I admire its literature in translation.

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.

Nor are we the culmination of evolution, except in the sense that there has never been another species so bizarrely ingenious that it could create both iambic pentameter and plutonium.

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

Of course anyone who truly loves books buys more of them than he or she can hope to read in one fleeting lifetime. A good book, resting unopened in its slot on a shelf, full of majestic potentiality, is the most comforting sort of intellectual wallpaper.

Results are no good unless they answer (or can be made to seem to answer, or can be twisted and wrenched and piled into odd shapes until they hint at being somehow perhaps on the verge or answering) a question that someone might conceivably want asked.

I used to read only fiction. Now I don't read much, only occasionally, such as a Cormac McCarthy or a Jim Harrison novel.

The swallow that hibernates underwater is a creature called yearning.

Wallace's sales agent, back in London, heard mutterings from some naturalists that young Mr. Wallace ought to quit theorizing and stick to gathering facts. Besides expressing their condescension toward him in particular, that criticism also reflected a common attitude that fact-gathering, not theory, was the proper business of all naturalists.

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.

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?

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.