Meaning of Life....

It’s hard to think of a word more charged with meaning—or meanings—than “life.” Some of the most passionate debates of our day, over stem cells or the right to die, genetically modified food, or wartime conduct, revolve around it. Whether we’re talking about when life begins or when it ends, the sanctity of life, or the danger of playing God, we all have an idea of what we mean when we talk about life. Yet, it often turns out, we actually mean different things. Scientists, despite their intimacy with the subject, aren’t exempt from this confusion.

“There is no one definition that we agree upon,” says Radu Popa, geobiologist and the author of Between Probability and Necessity: Searching for the Definition and Origin of Life. In the course of researching his book, Popa started collecting definitions that have appeared in the scientific literature. He eventually lost count. “I’ve found at least three hundred, maybe four hundred definitions,” he says.

It’s a peculiar state of affairs—biologists have learned more in the past decade about how living things work than we’ve learned collectively over the past several centuries—and an intense debate has arisen over what to do about it. Some are skeptical of science’s ability to come up with a definition of life that’s accurate enough to be meaningful, while others believe a definition is not just possible but essential for the future of biology.

“A science in which the most important object has no definition—that’s absolutely unacceptable,” says Popa. “How are we going to discuss it if you believe the definition of life has something to do with DNA and I think it has something to do with dynamic systems? We cannot have a conversation on any level. We cannot make artificial life because we cannot agree on what life is. We cannot find life on Mars because we cannot agree on what life represents.”

Recently, a new voice has entered the debate. Carol Cleland, who teaches philosophy at the University of Colorado and works with the NASA Astrobiology Institute—essentially as their philosopher-in-residence—is making a more radical argument: Scientists should simply give up looking for a definition of life. They can’t even begin to understand what life really is, she claims, until they find forms of life profoundly different from those we know here on Earth. Only when we can compare alien life with life on our planet will we understand the true nature of this ubiquitous, ephemeral thing.

Cleland believes biologists need to build a theory of life, just as chemists built a theory of the elements and physicists built a theory of electromagnetism. Definitions, she argues, are concerned only with language and concepts, not true understanding. By taking the semantics seriously, Cleland is calling for nothing less than a scientific revolution. Only when we change the way we think about life, she argues, will the true study of it begin.

The modern search for a definition of life was framed by a slender book published in 1943, called simply What Is Life? Its author was not a biologist, but a physicist. Erwin Schrödinger, who won the Nobel Prize for his work on quantum physics in 1933, was fascinated by how life seemed to defy the laws of physics. While the universe veered toward entropy, living things somehow created order on a molecular scale. And, somehow, living things could pass on that order from one generation to the next for millions of years.