Review ‘Life’s Edge’ – NEMO Kennislink

Growing human cells in the lab is no longer a surprise to anyone. Not even if those cells grow together into miniature versions of organs, the so-called organoids. Think of mini-intestines or mini-lungs to test the effect of medicines. Organoids are alive because they are made up of living human cells. Yet it is clearly not a mini-human in a bowl.

Carl Zimmer writes for the New York Times, National Geographic and The Atlantic, among others. Life’s Edge is his fourteenth book.

Only when it comes to organoids of brain cells do we view things slightly differently. Right at the beginning of his book Life’s Edge, acclaimed American science journalist and author Carl Zimmer takes you to a California lab where brain organoids are grown. Such a mini-brain is of course not a mini-human, but the neurons (nerve cells) in a brain organoid also fire signals that create measurable brain waves. And that makes the scientists involved and many others uncomfortable. What if a mini-brain develops consciousness? Do we still see it as nothing more than a clump of cells in a dish? Or will it become a new, independent form of life? When is something like this ‘alive’?

That question is the central theme of the book. Zimmer searches for the limits of life to get a grip on what life really is. Not a very original question in itself, because countless books and articles (and opinions) have been published about it. At the same time, no unequivocal and widely accepted answer has yet been found, so everyone can continue to shine their light on this. And Zimmer does that in an interesting and stimulating way.

Declared dead

In the strong opening of the book, he shows that the discussion about what life is, goes beyond an academic exercise. It is a discussion with direct practical consequences. Zimmer moves smoothly from brain organoids to the abortion battle. After all, it is also about the question of when a clump of cells changes into a life that has the right to exist. Is that after forty days of pregnancy? When a newborn breathes on its own? Once a fetus has a heartbeat? Or does life begin immediately after conception? Zimmer walks you through the arguments put forward by abortion opponents and immediately shows you where the holes are in their reasoning.

From the start of life it is a logical step to the end of life. Because what does death actually mean? Here, too, Zimmer is a fine guide through the history of thinking about and investigating death. Among others, Antoni van Leeuwenhoek and the writer Edgar Allen Poe – who feared nothing more than being buried alive – are reviewed. As well as the discovery of all kinds of microscopic little creatures that were ‘brought back to life’ after long periods of dehydration or freezing. Such as rotifers, nematodes (tiny worms) and tardigrades. Finally, Zimmer comes to the recent and bizarre story of an American girl who, after an operation to remove her tonsils, goes into cardiac arrest, is resuscitated and falls into a deep coma. Three days later, she is officially pronounced dead. She’s brain dead. But that is unacceptable to her desperate family, because her heart is still beating. The family does not give the hospital permission to stop the ventilator.


red maple, Acer rubrum, in the fall.

What follows is, in addition to an intensely sad situation for the family, years of marriage about the concept of brain death. And in fact we see the same here as with the abortion discussion, says Zimmer. Here, too, the key question is what it means to us to be ‘alive’. The question of when that will stop is just as pressing and complicated as when it will start. That discussion has not yet ended, but after five years the now 17-year-old girl still dies. Or again. Just how you look at it.

After these reflections on human life, Zimmer turns his gaze to other characters in the second part. He studies the five characteristics that keep cropping up as crucial to life: metabolism, information processing, homeostasis (internal balance), reproduction and evolution. Among other things, Zimmer visits a python collector to learn more about the special metabolism of these animals, sees how slime molds find their way in a maze (information processing) and goes in a cave in search of bats in hibernation (homeostasis). A very original find is that for the subject of reproduction, he visits a botanical garden to learn how maple trees work. You hardly come across the plant world in books about special life.


These chapters are all lively and engaging – Zimmer’s experience as science reporter splashes off the pages – but at the same time it is a set of incoherent reports about the research of apparently randomly chosen scientists. The third part is again completely different and in my opinion the highlight of this book. Zimmer describes here how research into what life is from the eighteenth century onwards takes shape in a ‘modern’ way. A surprising starting point for this story is the Sorghvliet estate in The Hague, where Count Bentinck appointed a certain Abraham Trembley as teacher to his two sons around 1740. This Trembley didn’t like the books and went out with the boys to discover and study nature for themselves. That led to groundbreaking discoveries, including the fascinating freshwater polyp Hydra. This special life form, somewhere in between plant and animal and that you can easily cut in half to get two new Hydras, completely turned the thinking about life and death upside down. Correspondence was fierce between Trembley and his fellow naturalists across Europe. Time and again life turned out to be full of surprises and the enthusiasm of these researchers makes Zimmer tangible by drawing on those letters.

From Trembley, Zimmer traces the history of scientific research into the essence of life roughly to the elucidation of the structure of DNA. Well-known names, but also forgotten thinkers pass by. You read about new insights that still hold true, but also about grandiose theories that turned out to be complete nonsense. In the fourth and final part, Zimmer steps into current events and describes ongoing research into the origin of life and attempts to create synthetic life. This part suffers from the same weaknesses as the second part. Here too we visit various scientists with Zimmer, but there is no cohesion. Nice reports, but why this particular research is highlighted is not always clear. Fortunately, Zimmer also knows how to tell these stories well, so that you are never reluctant to read.

Life’s Edge

Carl Zimmer, Penguin Books (2021), 348 pg, ISBN 978-0-593-18271-0

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