How do we define "life"? It's been tried many times, but there's always an edge case that makes a simple definition fall apart. Viruses can replicate, but not by themselves. Blood cells split and carry out life's functions, but have no DNA. Seeds can be completely dried for hundreds, even thousands of years, and still come back to life when conditions are rights. So can bacteria. Scientists have come up with definitions for life, but those definitions are often for use within their area of expertise, and do not cover all the uses of the word. There have been some who reject the very idea of a definition of life. Researchers at Lund University in Sweden carried out a survey not to define life, but to categorize it into something people can recognize when they see it.
The Lund researchers found that they could sort things pretty well into the living and the nonliving without getting tied up in an argument over the perfect definition of life. They propose that we can call something alive if it has a number of properties that are associated with being alive. It doesn’t have to have all those properties, nor does it even need exactly the same set found in any other living thing. Family resemblances are enough.
One philosopher has taken a far more radical stand. Carol Cleland argues that there’s no point in searching for a definition of life or even just a convenient stand‐in for one. It’s actually bad for science, she maintains, because it keeps us from reaching a deeper understanding about what it means to be alive. Cleland’s contempt for definitions is so profound that some of her fellow philosophers have taken issue with her. Kelly Smith has called Cleland’s ideas “dangerous.”
So not only is defining life difficult, the very nature of the quest to define it is a matter of contention. Read more about the topic in an excerpt from Carl Zimmer's new book Life's Edge: The Search for What It Means to Be Alive, at Quanta magazine. -via Damn Interesting