I marvel at the body's pickiness. Below 68 Fahrenheit, we shiver. Above 75, we sweat. From the near absolute zero of deep space to the sun's fiery core, the universe spans 30 million degrees, and our comfort range is seven degrees? Philosophers complain that the cosmos is harsh and inhospitable, but are we not astonishingly particular in our demands? We are like a beggar pleading to be fed with any of seven specialty foods.

Amazingly, the earth obliges us with a tolerable if not ideal climate—provided we do not venture five miles above or below this planet's surface, our narrow safe zone. At a picnic on a perfect spring day, there is boiling magma beneath the thin dirt floor we stand on. Meanwhile the air overhead, where planes are flying, would frostbite our skin and kill us with hypothermia.