Human Nature: Science, Technology, and Life.

Napping, Sex, and Abstinence

Which is more important: food, sleep, or sex? My instinct is to go with sleep, on the grounds that if you try to avoid all three, sleep is the one that will overtake you first. It's the one you need most. If that's true—and if we know that it's unreasonable and dangerous to insist that people abstain from sex—then isn't it stupid to expect pilots to abstain from sleep?

More here.