Nor do we know how life began. At some point, the Earth made the transition from chemistry to biology, yes, but we cannot “agree on a definition that separates the nonliving chemistry from life,” as the geneticist Johnjoe McFadden puts it. (He then paraphrases the astronomer Fred Hoyle, who famously said that the odds of assembling something like a bacterium out of the primordial ooze were akin to the odds of a tornado’s assembling a jumbo jet out of a junkyard heap as it sweeps through.)
There are scientists who will go so far as to say that life is a spectacular fluke. Not everyone, mind you: Researchers now estimate that there are one billion Earthlike exoplanets in the Milky Way. “To my mathematical brain, the numbers alone make thinking about aliens perfectly rational,” Stephen Hawking has said.
But a powerful essay by the evolutionary biologist Matthew Cobb will make you wonder whether any form of multicellular life is far less likely than one in a billion. He points out that “there are more single-celled organisms alive on Earth than there are Earthlike planets in the observable universe”; that the number of single-celled organisms that have lived on this planet over the course of 3.8 billion years is beyond calculation; that these organisms have interacted “gazillions” of times (I love it when words of the appropriate magnitude desert even the experts). Yet we’ve never had a second instance of eukaryogenesis — that remarkable moment when one unicellular life form lodged inside another, forming something much more complex — in all this time.
--Jennifer Senior, NYT, on the uniqueness of life as we know it