Anthropologist Stewart Guthrie's classic book Faces in the Clouds presents the fascinating thesis that religious thought is the accidental by-product of an evolved psychological system that's been designed to detect signs of other creatures in the natural environment. In the evolutionary past, Guthrie says, our ancestors needed to be especially vigilant of potential threats in the environment; these threats included not only predatory animals but, perhaps even more significantly, other people as well.

The general idea makes good sense adaptively. If you're out for a hike in the Sierra Nevada and in the distance ahead you make out an ambiguous object--could be an oddly shaped boulder, could be a snoozing Grizzly Bear--you'd be much better off erring on the side of the carnivorous 900-pound beast than the agglutination of phosphate. Since our brains have been hardwired to scan our surroundings for animals and other people then, argues Guthrie, it's quite by evolutionary accident that today we see Jesus Christ's face in the fur of a kitten born in the suburbs of South Bend or his mother Mary in the glass panel of a television cabinet in the Philippines.

It's not just religious concepts that trigger these false alarms, of course. Abraham Lincoln has made his appearance on many a potato chip over the years. Nor are these misattributions always fodder for fools. In Belfast there's a rocky mountainside on the city's northerly skyline that vaguely resembles the head of a giant with his neck craned back so that his nose touches the clouds. Legend has it that this resting colossus inspired Jonathan Swift to write his famous Lilliput scene in Gulliver's Travels.