The physicist and the dawn of the double helix

 

 

Three quarters of a century ago, Nobel laureate Erwin Schrödinger published What Is Life?, which described the forays of a “naïve physicist” into biology and suggested that hereditary properties are encoded in an “aperiodic crystal.” A meme was born that changed the life sciences forever.

 

 

 

A refugee from the Third Reich, Viennese-born Schrödinger had found shelter at Dublin’s Institute for Advanced Studies (1). Required by statute to deliver public lectures every year, he chose in 1943 for his topic the physical aspects of the living cell. He lectured on three consecutive Fridays, to a packed house. The enthusiastic response spurred the publication of his notes in November 1944.

The book did well. In the first year, it sold 5000 copies and attracted 65 reviews. The celebrated J. B. S. Haldane mused that at a time when most physicists were engaged in war work and had a hard time keeping up with their own subject, Schrödinger—in neutral Ireland—had found leisure enough to turn to another branch of science: genetics (2). Schrödinger had hailed the discipline as “easily the most interesting of our days.” Geneticist Haldane politely wondered whether posterity would confirm that judgment. It did, not least thanks to Schrödinger’s book.

What Is Life? became one of the most important science books ever, not for its content (whose limitations were soon evident) but for its influence on a cohort of brilliant scientists. Almost all of the protagonists of the double helix saga acknowledged, at one time or another, the impact of Schrödinger’s book (the one possible exception being crystallographer Rosalind Franklin, who died before writing her memoirs) (3). Many of them—including Francis Crick, Maurice Wilkins, and Seymour Benzer—were physicists, but some were chemists (such as Erwin Chargaff and Gunter Stent) or physicians (such as François Jacob). Even a teenage bird watcher named James Watson became “polarized towards finding out the secret of the gene” after reading Schrödinger’s booklet (4).

Schrödinger’s prescient vision of genetic coding is one message in What Is Life?. Another is that cells create order from disorder and transmit order from order. From this, Schrödinger concluded that new physical laws were needed to explain life: “,,,present-day physics and chemistry could not possibly account for what happens in space and time within a living organism.” He purported to prove this by drawing on the results of mutagenesis experiments conducted by his erstwhile postdoc Max Delbrück, which offered an estimate for gene size and implied, so Schrödinger thought, that heredity relies on a mechanism “that cannot be reduced to the ordinary laws of physics.”

Schrödinger was in good company: His colleagues Niels Bohr and Pascual Jordan were also of the opinion that new laws of physics were needed to explain life. With the discovery of the double helix, however, it turned out that there was no need for new laws. The chemical gadget could be entirely explained, ironically, by the quantum mechanics that Bohr, Schrödinger, Jordan, and others had developed in the 1920s. Indeed, the copying mechanism of genes is based on hydrogen bonds between complementary nucleotides—territory ruled by the Schrödinger equation.

Six months after the discovery of the double helix, and a mere 10 years after the Dublin lectures, Francis Crick sent a letter to Schrödinger, acknowledging the impact of What Is Life? on both himself and Watson. Schrödinger did not reply. Even stranger, he never returned to biology.

Schrödinger lived until 1961, when the search for the genetic code was at its height, but seems to have lost interest in “the most interesting science of our day.” He had assiduously studied genetics for 20 years, but after the publication of What Is Life? he turned to other things. In new editions of his seminal book—which never went out of print—Schrödinger did not address the breathtaking progress that it had caused, nor Oswald Avery’s discovery that genes are made of DNA, nor John von Neumann’s bold ideas on self-replicating automata.

With the advent of molecular biology, the centuries-old debate between “vitalists” and “mechanists” turned decisively against the former. Schrödinger, however, punctured the latter, in a jaunty afterword tackling consciousness. Haldane quipped in his book review, “A mechanist must either give a mechanist account of life, or turn a somersault. In his epilogue, Schrödinger does the latter with very great elegance.” Schrödinger had preempted that objection by quoting the philosopher Unamuno: “If a man never contradicts himself, the reason must be that he virtually never says anything at all.”

 

 

(원문: 여기를 클릭하세요~)