The Search for What It Means to Be Alive
By Carl Zimmer
Ask biologists what they study and the answers will quickly home in on living things, on particular lifeforms that they've spent countless hours thinking, scrutinizing, analyzing, and toiling over. Yet one further question – what exactly is a living thing? – is a sure-fire ticket to hesitation.
It's a good question, and it's tackled by science writer Carl Zimmer in Life's Edge: The Search for What It Means to Be Alive. The book compels readers to contemplate how possibly to define what makes something alive by melding scientific snippets on diverse lifeforms, historical tales, personal anecdotes, and a bit of philosophy. From the beginning we are introduced to a menagerie that perches in the gray area between alive and not-alive: creatures like tardigrades and nematodes that can reemerge from cryptobiosis with the touch of water, pythons whose basal metabolic rates can grind almost to a halt, slime molds that display a brainless kind of memory and problem-solving ability, and a girl named Jahi McMath, who was declared brain-dead yet had a beating heart and continued to grow before dying (again) five years later. SARS-CoV-2 makes an appearance, since a book on the definition of living would not be complete without a look at viruses. We are introduced to various definitions of life, sourced from scientists to philosophers, and we find that these telescope down to five special hallmarks: metabolism, information gathering, homeostasis, reproduction, and evolution. It's through bizarre and wondrous flora and fauna that the sheer diversity within these traits is shown, and the elusively complex nature of defining life made palpable. As quoted in Life's Edge, biology is indeed a "science in which the most important object has no definition."
Bizarre creatures have long been involved in defining the frontiers of life, as we see with the book's turn towards the historical. In the 1700s, Swiss naturalist Abraham Trembley discovered the regenerative ability of Hydra as he sliced and diced and regrew whole organisms from those little "polyp" pieces. We are introduced to the mechanical vision of life propelled by Descartes' writings, and to the vitalist movement, which opposed the former and believed that all living things possess a special life force. We learn of red herrings, like the 1800s discovery of a "living jelly" from the ocean, Bathybius, which turned out to be gypsum reacting with alcohol to form a gelatinous product, and the 1900s discovery of "microscopic creatures" dubbed radiobes, which turned out to be compounds formed when radium encounters bouillon. We meet a multidisciplinary cast of scientist protagonists who have tried to bottle up a definition of life, from a physiologist moonlighting as a spy, to physicists like Bohr, Delbrück, and Schrödinger tackling biology through the physicist's lens, and all the while, the NASA definition of life – "life is a self-sustained chemical system capable of undergoing Darwinian evolution" – grows increasingly flimsy.
I especially enjoyed the highlighted connection between biology and creative writing. We are introduced to the grandfather of Charles Darwin, Erasmus Darwin, whose poetry propelled the idea of evolution into the public eye (ideas later to be expounded upon by his grandson). The poet's proposal that simple life-forms arose from organic matter inspired a bevy of writers, including none other than Mary Wollstonecraft Shelley. From this interest in lifeforms and the 1800s notion that electricity was intimately linked to life arose the novel Frankenstein, in which the titular scientist brings his monster to life using electricity. This snippet was a fascinating illustration of the synergy between science communication, science fiction, and scientific research, at work since one of the earliest science fiction novels.
Frankenstein's fictional techniques were a harbinger of the spark essential to the 1952 Miller-Urey experiment, that landmark in origins-of-life research immortalized in literature and textbooks. Life's Edge contains a condensed survey of historical origins-of-life research, and here it transitions from a narrative of scientific snippets and history into one composed more of personal vignettes. Unlike Michael Marshall's The Genesis Quest (a comprehensive read on Origins research that we previously covered on the blog), Life's Edge contains a more personal take with anecdotes and Zimmer's encounters with scientists. Featured prominently is David Deamer, a major proponent of the hypothesis that the origins of life lie in liposomes and volcanic hot spring pools, and a multidisciplinary bunch of scientists whose collaborative work revolves around protocells, simple lipid-membrane vesicles reminiscent of primitive cells.
I enjoyed the book. It was a thought-provoking pop-sci read that brought the lab environment alive and painted a switchback path of inquiry, mistakes, and discoveries. Zimmer's writing is enjoyable and accessible: at times suspenseful, at times lyrical, always carrying an undercurrent of wonderment with the natural world.
The book evokes a palpable excitement in learning about the diverse attempts at defining life. It reminded me of the enjoyment found in reading old library books marked up by previous readers: in the underlining of certain sentences, or in the brief thoughts scribbled along page margins, the next reader can observe a communal effort to find meaning. To some, it's off-putting vandalism; to others, it's a peek into other people's minds and history. The value in these mark-ups – and in the quest to delineate what is alive – may not be in which exact words are highlighted or circled, but rather in the process of discovery.
I happened to read Life's Edge around the same time I read The Book of Disquiet by the Portuguese writer Fernando Pessoa. The two books synergized. They both read to me as appreciations of the uncertainty of all things and the creativity that arises as a result. In the words of the protagonist in the latter book, "the oracles who said 'Know thyself' proposed a task greater than all of Hercules' labours and an enigma even more obscure than that of the Sphinx.'" Undoubtedly an apt description.
The answer to what is life? has undergone a kind of evolution itself, and Life's Edge is an adept tour guide to that convoluted path.