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What Is Life? Its Vast Diversity Defies Easy Definition.

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Carl Zimmer writes in Quanta:

People often feel that they can intuitively recognize whether something is alive, but nature is filled with entities that flout easy categorization as life or non-life — and the challenge may intensify as other planets and moons open up to exploration. In this excerpt from his new book, Life’s Edge: The Search for What It Means to Be Alive, published today, the science writer Carl Zimmer discusses scientists’ frustrated efforts to develop a universal definition of life.

“It is commonly said,” the scientists Frances Westall and André Brack wrote in 2018, “that there are as many definitions of life as there are people trying to define it.”

As an observer of science and of scientists, I find this behavior strange. It is as if astronomers kept coming up with new ways to define stars. I once asked Radu Popa, a microbiologist who started collecting definitions of life in the early 2000s, what he thought of this state of affairs.

“This is intolerable for any science,” he replied. “You can take a science in which there are two or three definitions for one thing. But a science in which the most important object has no definition? That’s absolutely unacceptable. How are we going to discuss it if you believe that the definition of life has something to do with DNA, and I think it has something to do with dynamic systems? We cannot make artificial life because we cannot agree on what life is. We cannot find life on Mars because we cannot agree what life represents.”

With scientists adrift in an ocean of definitions, philosophers rowed out to offer lifelines.

Some tried to soothe the debate, assuring the scientists they could learn to live with the abundance. We have no need to zero in on the One True Definition of Life, they argued, because working definitions are good enough. NASA can come up with whatever definition helps them build the best machine for searching for life on other planets and moons. Physicians can use a different one to map the blurry boundary that sets life apart from death. “Their value does not depend on consensus, but rather on their impact on research,” the philosophers Leonardo Bich and Sara Green argued.

Other philosophers found this way of thinking — known as operationalism — an intellectual cop‐out. Defining life was hard, yes, but that was no excuse not to try. “Operationalism may sometimes be unavoidable in practice,” the philosopher Kelly Smith countered, “but it simply cannot substitute for a proper definition of life.”

Smith and other foes of operationalism complain that such definitions rely on what a group of people generally agree on. But the most important research on life is at its frontier, where it will be hardest to come to an easy agreement. “Any experiment conducted without a clear idea of what it is looking for ultimately settles nothing,” Smith declared.

Smith argued that the best thing to do is to keep searching for a definition of life that everyone can get behind, one that succeeds where others have failed. But Edward Trifonov, a Russian‐born geneticist, wondered if a successful definition already exists but is lying hidden amidst all the past attempts.

In 2011, Trifonov reviewed 123 definitions of life. Each was different, but the same words showed up again and again in many of them. Trifonov analyzed the linguistic structure of the definitions and sorted them into categories. Beneath their variations, Trifonov found an underlying core. He concluded that all the definitions agreed on one thing: life is self‐reproduction with variations. What NASA’s scientists had done in eleven words (“Life is a self‐sustained chemical system capable of undergoing Darwinian evolution”), Trifonov now did with three.

His efforts did not settle matters. All of us — scientists included — keep a personal list of things that we consider to be alive and not alive. If someone puts forward a definition, we check our list to see where it draws that line. A number of scientists looked at Trifonov’s distilled definition and did not like the line’s location. “A computer virus performs self‐reproduction with variations. It is not alive,” declared the biochemist Uwe Meierhenrich.

Some philosophers have suggested that we need to think more carefully about how we give a word like life its meaning. Instead of building definitions first, we should start by thinking about the things we’re trying to define. We can let them speak for themselves.

These philosophers are following in the tradition of Ludwig Wittgenstein. In the 1940s, Wittgenstein argued that everyday conversations are rife with concepts that are very hard to define. How, for example, would you answer the question, “What are games?”

If you tried to answer with a list of necessary and sufficient requirements for a game, you’d fail. Some games have winners and losers, but others are open‐ended. Some games use tokens, others cards, others bowling balls. In some games, players get paid to play. In other games, they pay to play, even going into debt in some cases.

For all this confusion, however, we never get tripped up talking about games. Toy stores are full of games for sale, and yet you never see children staring at them in bafflement. Games are not a mystery, Wittgenstein argued, because they share a kind of family resemblance. “If you look at them you will not see something that is common to all,” he said, “but similarities, relationships, and a whole series of them at that.”

A group of philosophers and scientists at Lund University in Sweden wondered if the question “What is life?” might better be answered the way Wittgenstein answered the question “What are games?” Rather than come up with a rigid list of required traits, they might be able to find family resemblances that could naturally join things together in a category we could call Life. . . .

Continue reading. There’s more.

Written by Leisureguy

9 March 2021 at 6:15 pm

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