Life’s Edge: Searching for What It Means to be Alive by Carl ZimmerLife’s Edge: Searching for What It Means to be Alive by Carl Zimmer

Life’s Edge: Searching for What It Means to be Alive by Carl ZimmerIn the past year alone, humans have landed multiple devices on Mars, retrieved samples from the Moon and not one but two asteroids, delved ever deeper into the Earth, and shattered records for the recovery of DNA from ever-older specimens. Meanwhile, plans are being hatched to zip a helicopter around Titan to examine its pools of liquid hydrocarbons, fly a probe through the geysers of Enceladus to collect samples, scoop surface ice off Europa, and use the next generation of space telescope to examine the atmospheres of exoplanets light-years away. All in the search for life.

Given all that time, effort, and money, one could be forgiven for assuming that we know what we’re looking for. But, as Carl Zimmer makes explicitly clear in his newest popular science work, Life’s Edge: Searching for What It Means to be Alive (2021), that’s not even close to reality.

Turns out we not only don’t know the meaning of life (OK, 42); we don’t even know what it means to be alive. To try and circle around the question, if not arrive at an actual answer, Zimmer has penned a series of linked essays that explore various aspects of the mystery and the many attempts, historical and contemporary, to solve it through various means: chemistry, biology, physics, philosophy, astronomy.

He travels to a mine in the Adirondack Mountains of NY to count hibernating bats, to laboratories to watch slime molds find the shortest path to food, to a New England Arboretum to learn how maples reproduce, to the Jet Propulsion Lab to interview astrobiologists about NASA’s search for life. He explores the long-running medical problem of when to declare someone dead — Is it when the heart stops? The lungs? Brain activity? — as well as the just as long debate between vitalists, who believed in a “vital force that endowed matter with self-directed motion [and] purpose, and Cartesians and their “machine-centered view of life … seeing themselves in league with clock repairman.” And finally he ends just where one might expect in a book that begins with questions of how life began — in several labs trying to create life anew.

Along the way we get some familiar definitional parameters: life has to reproduce, life has to metabolize (eat and turn that food into energy), life has to evolve, and others. And just as quickly as Zimmer offers up these requirements, he shows us the exceptions or at least the boundary-blurrers, such as computer programs that evolve in self-directed manner and tardigrades that enter a weird no-person’s land between life and death (here you might ponder the thought that tardigrades might even now be living on the Moon, thanks to a crashed probe).

It’s all endlessly fascinating, not in spite of life’s ambiguities and contradictions, but because of them. Zimmer doesn’t appear to have any leanings one way or the other on the various theories, at least not one that shows, but what shines throughout Life’s Edge is his curiosity and his desire to explore all nooks and crannies, including not just scientists but also writers and philosophers. Nor does he highlight only the “successes,” since science advances as much via what some might call its “failures” (or at least errors), which Zimmer treats with the same respect as he does those theories that have better withstood the test of time. Meanwhile, his prose is always clear and smooth, and his explanations never get bogged down in too much detail or complexity. Sometimes a few of the sections feel like they end a bit abruptly, or the linkages could be a little smoother, but these were niggling issues in an otherwise informative and fascinating work. In the end, you won’t have an answer to, “What is Life,” but you’ll be exhilarated at the journey to find out.

Published in March 2021. We all assume we know what life is, but the more scientists learn about the living world—from protocells to brains, from zygotes to pandemic viruses—the harder they find it is to locate life’s edge. Carl Zimmer investigates one of the biggest questions of all: What is life? The answer seems obvious until you try to seriously answer it. Is the apple sitting on your kitchen counter alive, or is only the apple tree it came from deserving of the word? If we can’t answer that question here on earth, how will we know when and if we discover alien life on other worlds? The question hangs over some of society’s most charged conflicts—whether a fertilized egg is a living person, for example, and when we ought to declare a person legally dead. Life’s Edge is an utterly fascinating investigation that no one but one of the most celebrated science writers of our generation could craft. Zimmer journeys through the strange experiments that have attempted to re-create life. Literally hundreds of definitions of what that should look like now exist, but none has yet emerged as an obvious winner. Lists of what living things have in common do not add up to a theory of life. It’s never clear why some items on the list are essential and others not. Coronaviruses have altered the course of history, and yet many scientists maintain they are not alive. Chemists are creating droplets that can swarm, sense their environment, and multiply. Have they made life in the lab? Whether he is handling pythons in Alabama or searching for hibernating bats in the Adirondacks, Zimmer revels in astounding examples of life at its most bizarre. He tries his own hand at evolving life in a test tube with unnerving results. Charting the obsession with Dr. Frankenstein’s monster and how Coleridge came to believe the whole universe was alive, Zimmer leads us all the way into the labs and minds of researchers working on engineering life from the ground up.


  • Bill Capossere

    BILL CAPOSSERE, who's been with us since June 2007, lives in Rochester NY, where he is an English adjunct by day and a writer by night. His essays and stories have appeared in Colorado Review, Rosebud, Alaska Quarterly, and other literary journals, along with a few anthologies, and been recognized in the "Notable Essays" section of Best American Essays. His children's work has appeared in several magazines, while his plays have been given stage readings at GEVA Theatre and Bristol Valley Playhouse. When he's not writing, reading, reviewing, or teaching, he can usually be found with his wife and son on the frisbee golf course or the ultimate frisbee field.

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