Life’s Edge: The Search for What It Means to Be Alive by Carl Zimmer is published by Picador (£20). “But then everyone will go: ‘Oh, that was easy.’” “I’m pretty sure we will crack the origin-of-life problem in the next few years,” he says. Cronin’s droplets may even, one day, be declared alive. The idea is that some of the droplets will spark complex reactions, creating new compounds that can store information – a condition of life. But they could be a dry run for making it.” The robot is “programmed with curiosity” and learns from the experiments, creating droplets in petri dishes: “these lifelike droplets, these skittering blobs of active matter, are not life. He has built a robot that can carry out thousands of experiments mixing various chemicals in a petri dish: the raw materials, he hopes, for creating life. One of the originators of this theory of life is a chemist, Lee Cronin, who has devised an ingenious experiment to demonstrate assembly theory at Glasgow University. This may reveal a distinction between random chemistry and living things: “Life is a state of matter that can spontaneously make things with a lot of assembly steps.” A simple molecule may need just a single step to form from atoms, but a living organism needs far more: materials made by living things need more than 15 steps – they are exquisitely complex. It’s called “assembly theory”, and essentially it calculates the number of steps it takes to build something. One new theory explains life as a special way of putting things together. Instead, she argues, scientists should be working towards a theory that explains life non-scientists may be surprised that one doesn’t exist already. But life is not the sort of thing that can be defined simply by linking concepts: “We don’t want to know what the word life means to us,” she says. According to Zimmer, they “straddle life’s edge”.Ĭarol Cleland, a philosopher who has worked with Nasa’s Astrobiology Institute, tells Zimmer that the search for a definition of life is pointless. But many scientists say that, strictly speaking, they are not alive, as they need another creature’s cells to multiply. But are they alive? They certainly evolve like other forms of life, as we see from the new variants of Covid-19 that are constantly emerging. There are more viruses in a litre of seawater than there are in human beings. But if you pour water on a dried-out tardigrade, in a matter of minutes it becomes a moving, feeding, reproducing animal.” Known as “cryptobiosis”, this is a third state, between life and death. Other creatures can, too: “If you pour water on someone who has just died from dehydration, they will not sit up. One that had been dried out and frozen in a glacier was revived after 600 years. Photograph: Tristar Pictures/Allstarīut what about those things that dwell at “life’s edge” and test the limits of our definitions? Mosses can survive desiccation. The nature of life … Kenneth Branagh as Victor Frankenstein in the 1994 film adaptation. They include metabolism (the living alchemy by which food is turned into energy), information gathering, homeostasis (how an organism preserves within itself the conditions of life), reproduction and evolution. There are also widely accepted “hallmarks” of life. Our brains are very good at spotting signs of life, recognising complex movements and trying to read intentions into them. Victor Frankenstein, the scientist in the novel who reanimates a stitched-together corpse, is obsessed with the question: “Whence, I often asked myself, did the principle of life proceed?” This helped inspire one of the most famous and disturbing fictions about the nature of life – Mary Shelley’s Frankenstein (1818). Charles Darwin’s grandfather, Erasmus Darwin, anticipated evolution by suggesting that this force was passed down from one generation to the next, changing over time to produce different forms. Others disagreed, arguing that life was distinguished by a “vital force”. In this subtle and profound meditation on the science of life, filled with memorable insights into the past and future of biology, Zimmer reveals the extraordinary complexity and diversity of life, as well as the ingenious attempts of scientists to probe its origins and how it may have evolved on other worlds.ĭescartes thought life was explained by matter in motion: animals were just complicated clockwork mechanisms.
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