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 ¡ª 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.