The Restless Clock: A History of the Centuries-Long Argument over What Makes Living Things Tick

If you think the debate over what makes living things tick is a recent scientific puzzle, think again. Jessica Riskin’s “The Restless Clock” takes us back to the 1600s and drags us through a centuries-long argument that’s as much about philosophy as it is about biology. At its core, the book tackles a surprisingly stubborn question: are living beings just complex machines, or do they possess some kind of inherent agency — a purposeful spark that can’t be reduced to gears and chemistry?

Riskin’s journey starts with the early modern era, where mechanical automata—clockwork dolls and other intricate devices—captivated thinkers and blurred the line between the living and the manufactured. These automata weren’t just toys; they were models for how life might work. If humans could build machines that mimicked life’s motions, maybe organisms were just fancy machines themselves. René Descartes famously took this idea to heart, arguing that animals were essentially soulless automata, acting solely on mechanical principles without any inner experience or purpose. But not everyone bought that.

Enter Gottfried Wilhelm Leibniz, who pushed back against the soulless machine idea with his concept of monads—tiny, indivisible units of life that carried an intrinsic purpose. Leibniz’s vision added a metaphysical twist to the debate, insisting that life can’t be fully explained by mechanical parts alone. Riskin traces how this push and pull between mechanism and vitalism (the belief in a life force beyond physical parts) played out over the centuries.

What’s fascinating is how this debate never really went away. Even Darwin’s theory of evolution, which you might assume would settle the mechanistic argument by explaining life’s complexity through natural selection, didn’t close the book. Instead, it shifted the conversation. The question became: can natural selection alone account for agency and purpose, or is there still room for something else?

Riskin doesn’t just stick to dusty history. She connects these centuries-old ideas to ongoing debates in evolutionary biology, cognitive science, and artificial intelligence. For example, when AI researchers try to build machines that ‘think’ or ‘decide,’ they’re wrestling with the same core issue: can agency be reduced to algorithms and circuitry, or is it fundamentally different in living beings?

The book shines because Riskin writes like she’s telling you a story over coffee—clear, engaging, and down-to-earth. She’s not trying to dazzle with jargon or pretend there’s a neat answer. Instead, she shows how the question of agency is a restless one, always evolving and never fully settled. Her interdisciplinary approach—mixing history, philosophy, and science—gives the whole saga a lively texture.

That said, the book isn’t perfect. Some readers might find that Riskin leans heavily on historical figures and ideas, sometimes at the expense of deeply engaging with how current science deals with agency. The dominant mechanistic view in modern biology and neuroscience gets less critical scrutiny than you might expect, which could leave readers wanting a sturdier bridge from past debates to today’s scientific realities. Also, while the historical sweep is impressive, the book occasionally feels like a museum tour rather than a sharp, focused argument.

Still, if you’re interested in how humans have wrestled with the mystery of life—not just as a biological fact but as a philosophical puzzle—this book offers a rich, thought-provoking ride. It reminds us that the question “What makes life tick?” is more than academic curiosity. It shapes how we see ourselves, our machines, and the blurry line between the two.