So you're a human being. Well, isn't that special?

So far, popular reaction to NASA's announcement that its scientists have discovered evidence of life in a meteorite from Mars has been pretty positive. Only a few cynics have accused the space agency of a ploy for more funding. But that may change as the implications sink in. Last week's announcement is the biggest insult to the human species in almost 500 years, step two in a three-step process that will leave humanity totally humbled.

Ptolemy (second century) was the first and boldest in a long succession of spin doctors for the primacy of human beings. The whole universe, he postulated, rotated around us, with the Earth sitting at the center of heaven itself. Any marketing consultant will tell you that positioning is everything, and center-of-the-universe is hard to beat.

A Polish astronomer named Copernicus (1473-1543) rudely pointed out: Sorry earthlings, we spin around the sun, not vice versa. This might have made Copernicus unpopular, if he hadn't had the good sense to die the day his book went to press. His follower, Galileo Galilei (1564-1642), built a telescope and used it to piss in the soup even more. The sun, it seemed, has spots on it. Far from being the perfect furnace of heaven, it has a face covered with celestial zits. The moon is an uneven and pockmarked rock, and Jupiter upstages Earth by having multiple moons. The sky went from being a perfect clockwork centered on Earth to a fairly shabby neighborhood in which we were a minor resident.

This revelation was disquieting enough that the authorities of the time sought the only rational solution--they decided to burn Galileo alive if he didn't recant. Eventually Galileo did sign a decree saying that the Earth sat at the center of the universe, while muttering, "Eppur si moeve" ("But it still moves") under his breath. Giordano Bruno, a sort of 16^th-century Carl Sagan, popularized these concepts without repenting, saying, among other things, that "innumerable suns exist. Innumerable earths revolve around those suns. Living beings inhabit these worlds." A soundbite like that would have gotten Bruno his 15 minutes of TV celebrity if he'd been around last week. But this was 400 years ago, so they roasted him to death instead.

Bruno's crime, like Galileo's, was to undermine the uniqueness of our planet, and by doing so, to threaten the intellectual security of the religious dictatorships of his time. People get cranky when you burst their bubble. Over time, advances in astronomy have relentlessly reinforced the utter insignificance of Earth on a celestial scale. Fortunately, political and religious leaders stopped barbecuing astronomers for saying so, turning their spits with human-rights activists instead.

But the hubris that makes us insist on a special role for humans and Earth didn't disappear: It just found other bases. Among the sciences, biology became the last refuge, for within its realm, Earth was still special. Life was the unique and sacred phenomenon of which we humans were the crowning glory. Consciously or not, mainstream opinion in biology--until last week--orbited around the essential mystery of life on Earth just as surely as the Ptolemaic view was lodged in the firmament. Only a few brave scientists violated the taboo and speculated on life beyond Earth.

Most visions of extraterrestrial life are actually steeped in human hubris. The fictional extraterrestrials of StarTrek or a hundred other space operas are less alien than many of my neighbors. And funny, the ones running the place are mostly WASPish men. A galaxy full of these folks is no stranger than a Kiwanis club meeting: We have met the aliens, and they are us! Darker visions of life beyond earth support human supremacy in another way. After all, even the most monstrous and advanced alien foe can be vanquished by the likes of Sigourney Weaver or Will Smith. For that matter, those hapless aliens can't stay ahead of the doughty X-Files team without a conspiratorial collaboration with that least effective of all entities, the U.S. government.

Alien stories that are claimed as true are no better. Why Earth would be such a fascinating place for UFOs to visit is left unexplained. I mean, really: Roswell, N.M.? Inevitably, the UFO stories climax in the ultimate tribute to human ego. The aliens, it seems, have traveled umpteen billion miles so they can abduct us from our beds and have sex with us. I'm told that once you try a human, you never go back.

The NASA discovery suggests that life is probably a pretty ordinary phenomenon that occurs anyplace you give it half a chance. Earth isn't special. The alien life forms aren't special either. Instead of highly logical humanoids with pointy ears or other endearing characteristics, they seem to be a lot like simple bacteria. Should they invade, Will Smith can wipe them out with some Listerine.

When there's only one example of anything, its very uniqueness makes it special. Life on Earth was special because it was the only life we knew. In this case however, the dogma being shattered is based fundamentally on ignorance. Nobody knew whether there was life on Mars because, oddly enough, nobody had looked until now. The whole field of biology has rested precariously on a single data point--life on Earth. Last week, we got a second data point.