The showdown over the U.S. debt ceiling demonstrates a crucial failing of human beings: We are systematically incapable of understanding how precarious our existence, or the continuance of our currently familiar condition, really is.

Think carefully about life on this planet and you're inevitably led, as Charles Darwin was, to think about adaptation.

An organism's characteristics reflect the conditions under which its ancestors evolved — conditions that enabled them to survive at least well enough to have viable offspring. The fat of a hippopotamus, the sleek shape of a bird's wing represent well-tuned solutions to pressing problems.