Carl Zimmer on “Life’s Edge: The Search for What It Means to Be Alive”

Kathleen O'Neil

Science writer Carl Zimmer is a three-time winner of the AAAS Kavli Science Journalism Award and the author of 14 books, the newest of which is “Life’s Edge: The Search for What It Means to Be Alive.” The book, which was published March 9, explores how we struggle to define life and the ways life may have first begun on Earth and elsewhere.

Zimmer also writes the weekly “Matter” column for The New York Times and has contributed to The Atlantic, National Geographic, Time and Scientific American. Zimmer spoke with Kathleen O’Neil for AAAS, and their conversation has been edited for length and clarity.

Q. You mention in the book growing up in the sixties and seventies and watching the moon landings and Mars explorations. Has the possibility of finding life elsewhere and the question of what makes things alive been an interest of yours since you were young?

Carl Zimmer                 Photo by Mistina Hanscom

A. Oh, absolutely. I think being a child of the space age definitely made me think about life on Earth and maybe life elsewhere as well. And the fact that we haven't found it makes you wonder, well, what is it that we're actually looking for?

It is interesting that when we think about life, we don't consider that we may not have a good definition of life. We kind of know it when we see it. There seem to be hallmarks that both scientists and non-scientists alike look at and say, "Well, that's what I'm talking about when I'm talking about something alive."

So, I decided to start the book by really exploring what those hallmarks are and finding the strangest, most interesting examples I could think of. For homeostasis ― the ability to regulate temperature, blood sugar and the like ― I talk about a hibernating animal, like a bat, because they're shifting that balance so that they can go practically without eating or drinking for months on end and yet maintain that metabolic balance.

Slime molds, which are these incredible creatures that are all around us in the woods, are just these strings and masses of protoplasm pulsating through the forest floor. They're making all sorts of complicated decisions about what to do next. They are, in effect, making these subtle calculations about the best way to move around, to find food and to navigate their way through the world. And they're just these blobs. And so, even for the things we can all agree are alive, in a way they're just as mysterious as life itself.

Q. When you decided to write the book, did you already have an idea of everything you've included in it, or did you do research that led you in new directions?

A. I had been working over the years on various stories that all played role in the book. Some years ago I wrote about the philosopher Carol Cleland for a magazine article. She argues  that it’s impossible to define life because we need a theory of life, not a definition. I wanted to circle back to her and understand how her thinking had evolved and what other philosophers thought about this very provocative idea.

Sometimes when I start thinking about writing a book, it occurs to me that I've unconsciously already started writing it. I’ve been writing articles on different bits and pieces of the big story, and now I'm just starting to see them come together. There was a similar experience with my previous book, “She Has Her Mother's Laugh,” where I realized that heredity had been something I had been exploring in all sorts of different ways. With "Life's Edge," I was thinking maybe I need to do more research on this idea about the centuries-old struggle to make sense of life itself.

Q. Whenever researchers appear to make scientific progress in understanding how life works, it's gotten a lot of attention. Why does having a definition of life seem to matter to people?

A. I think it matters to us not just because we like to think about very weird things that are at the border between the living and the nonliving world. It also makes us think about ourselves. We are alive. And what does that mean? And when did our life come into existence and how exactly do we know when people are no longer alive? When we use the word “life,” it still is just an incredibly slippery word.

Q. When did you start mapping out the book?

A. I was putting together a proposal for this in 2019. I didn't really start working on it till the end of 2019 and into 2020.

Courtesy of Penguin Random House

Q. And then the coronavirus arrived.

A. In February [2020], I was planning the last four trips for my book. I'd already done some traveling. At the end of February, I went to this abandoned graphite mine in the Adirondacks with some scientists who are studying hibernating bats. That was an amazing experience. But I'm listening to the news on my drive back home about the pandemic and how it's moving out of China and just thinking, “Well, I don't think I'm doing anything else now. I'm just going to have to stay home.” So, I had to rethink how I was going to work on the book. In the end, it worked out well. It forced me to look with a cold eye at my manuscript and my outline and say, well, what do I really need here? Maybe I should just think about what I already have and how can I turn that into something crisp and focused. In the end, I think I wound up with a better book, ironically. And I also had a chapter on viruses, and that became a chapter very much about coronaviruses.

Q. Do you think scientists eventually will be able to agree on a definition of life?

A. In terms of understanding the machinery of life, we know it far better than people did in the 18th century. You know, we look at the coronavirus and how it latches onto our cells and gets inside. Scientists can understand that down to the level of atoms in terms of the physics and the chemistry that's involved, which is astonishing. Yet for all of that, if you ask scientists “Okay, you learned all these things, so what is life?” You literally get hundreds of different answers. I'm not exaggerating. And the scientists are very certain that they’re right. Anyone who has another definition is an idiot.

Some physicists I've spoken to are really quite confident that within a generation or two, life will come together as an interesting property of matter, the same way we have a good theory of superconductivity. We know why lots of different materials can display that property [the flow of electricity through a material with zero resistance.] They are pretty confident that life will turn out to be, like superconductivity, a fundamental property of certain well-defined types of matter.

Q. That's kind of mind-blowing to think about.

A. Yeah, that's why I wrote the book. The more I spoke with people, the more just fascinated I was by the ideas that people are working on.