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Thursday, December 1, 2022

Book Review: ‘Life’s Edge,’ by Carl Zimmer

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To understand the basis of life, Schrödinger argued, was to understand how information was encoded, transmitted and reproduced. Presciently, he predicted that life’s information was carried in a molecule, one that could provide a “code-script” for building an entire organism.

That molecule, of course, is DNA (or, in rare instances, RNA). Zimmer is particularly brilliant in telling the story of DNA. He takes us back to Cambridge, where a daydreaming physicist meets a voluble biologist: Watson bumps into Crick. Crick’s “bosses at the Cavendish discouraged him from his daydreaming, but in 1951 he met a young American visiting Cambridge who also loved ‘What Is Life?’ James Watson was happy to talk about DNA with Crick for hours on end.”

Zimmer cautiously condenses the story of the discovery — especially the remarkable role of Rosalind Franklin, who was meticulously working on DNA and on the verge of discovering its structure, and whose X-ray pictures Watson became privy to. The iconic structure of the DNA double helix makes its due appearance, but Zimmer is careful to note that this was just the beginning, not the end, of our mechanistic understanding of life, and of those who contributed to it. “Rosalind Franklin is missing from the photograph, for one thing,” he writes, giving Franklin her historical due.

But the structure of DNA, too, was merely a prelude to our understanding of life. Crick, Watson, Sydney Brenner, Matthew Meselson, Frank Stahl and Marshall Nirenberg, among many others, would carry forward the mission of deciphering how the “code script” written in the DNA molecule leads to how life “happens” — how it reproduces, and how the code is carried forward for generations. Franklin, unfortunately, would never get full recognition for her work: By the time the Nobel Prize for deciphering the structure of DNA was awarded, she had died of ovarian cancer.

The “new” biology, Zimmer points out, was no longer about the descriptive (how life is), but about the mechanistic (how life works). Crick wrote his own book — a sort of answer to Schrödinger’s, named “Of Molecules and Men” — which, while criticized for overly simplifying biology, was also praised for laying out a new manifesto. Life, according to Crick, was an epiphenomenon of physics and chemistry — complex, yes, but still explicable in molecular terms. At a NASA meeting in 1992, scientists captured this new big-picture definition in a sentence: “Life is a self-sustained chemical system capable of undergoing Darwinian evolution.” It was a synthesis, or perhaps an armistice, between the old and the new, between the physiologists and the molecular evolutionists. The “self-sustained chemical system” dismissed the idea that there was something special about living chemicals. But the idea of Darwinian evolution — at the molecular, or organismal, level — retained ideas from the 19th century.

In his final section, Zimmer turns, predictably, to viruses. This could hardly be more topical: A piece of RNA, packaged inside a molecular envelope, has gripped the globe and caused a pandemic, turning the world upside down. Again, his analysis of virology is succinct but allows for complexity: He acknowledges the debates in the field, and allows the reader an inner glimpse into how scientists are learning to think about these “borderlands” — microbes that are not alive, but can parasitize the biology of living beings.

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