11
EPILOGUE: “THE GREAT DESIDERATUM”

ST. ANDREWS DID NOT LOOK gray in the spring sunshine, although it was still cold. The North Sea breeze made it feel more like March than May. D’Arcy Thompson’s old house on South Street has a slate plaque outside commemorating his residence: “naturalist, scholar,” it calls him. I had come here—neatly but coincidentally, it was almost exactly a year after I’d had my metabolic rate measured—to see the archive of D’Arcy Thompson’s papers. I was hoping for a view into his mind, hoping to track the genesis of his ideas. I was also looking for an ending, some document, anecdote, or experience that would wrap things up tidily.

Sure enough, his notebooks cover the gamut—it was like seeing On Growth and Form chopped into bits and reassembled at random. There were stirring quotations: “The great desideratum for any science is its reduction to the smallest number of dominating principles.” There were notes on how larger animals had longer gestation periods, slower heartbeats, and longer lives. There was a paper comparing the metabolic rate of prawns from English and Arctic waters and a note on how herring eggs hatched quicker at higher temperatures. There were



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In the Beat of a Heart: Life, Energy, and the Unity of Nature 11 EPILOGUE: “THE GREAT DESIDERATUM” ST. ANDREWS DID NOT LOOK gray in the spring sunshine, although it was still cold. The North Sea breeze made it feel more like March than May. D’Arcy Thompson’s old house on South Street has a slate plaque outside commemorating his residence: “naturalist, scholar,” it calls him. I had come here—neatly but coincidentally, it was almost exactly a year after I’d had my metabolic rate measured—to see the archive of D’Arcy Thompson’s papers. I was hoping for a view into his mind, hoping to track the genesis of his ideas. I was also looking for an ending, some document, anecdote, or experience that would wrap things up tidily. Sure enough, his notebooks cover the gamut—it was like seeing On Growth and Form chopped into bits and reassembled at random. There were stirring quotations: “The great desideratum for any science is its reduction to the smallest number of dominating principles.” There were notes on how larger animals had longer gestation periods, slower heartbeats, and longer lives. There was a paper comparing the metabolic rate of prawns from English and Arctic waters and a note on how herring eggs hatched quicker at higher temperatures. There were

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In the Beat of a Heart: Life, Energy, and the Unity of Nature doubts that natural selection could explain the colors of insects or the shapes of leaves and horns. There were doodles of aeroplane and dragonfly wings, honeycomb, cell shapes, and bone structures. There were lists of numbers and sketched graphs and a correspondence with A. C. Aitken at the University of Edinburgh over some data D’Arcy had collected on the allometry of the stag beetle’s body parts. (“What is interesting in your sample is the disproportionate growth at different ranges of size—the larger beetle is not a magnification of the smaller one,” Aitken wrote.) There was speculation on diversity, from one of D’Arcy’s book reviews: “We begin by marvelling at the wealth of species in the world, and end by realizing that, in contrast to infinite variety, they are very few.” There was a letter of warning from Marcus Hartog, a leading cell biologist of the late nineteenth century: “I would advise you to be on your guard against the physicists: they love to simplify the problem out of all real relation to the facts of the organism.” Connections emerged; degrees of separation shrank. A quote from Alexander von Humboldt on the physiology of electric fish had been typed up and pasted into a notebook. Evelyn Hutchinson’s review of the second edition of On Growth and Form was stuck into Thompson’s own copy (“Sir D’Arcy still seems to us fresh from conversation with Aristotle, and still seems to have discussed his material with Galileo”). The editor of Nature had written, asking Thompson to adjudicate on whether a recent paper published in the journal by the Italian mathematician Vito Volterra had reproduced work already published by Alfred Lotka: “Volterra hasn’t got a leg to stand on,” D’Arcy concluded. The theorem, which models the effect that predators have on the numbers of their prey, and vice versa, is now called the Lotka-Volterra equation. A paper cut out of a 1936 edition of Nature suggested that Costa Rica’s plant diversity was due to its high mountains exposing species to mutation-causing cosmic rays. But yet again, the diversity of ideas and information threatened to become unmanageable. There were notes on the size of nitrogen atoms and comparisons of the size and density of the sun and Betelgeuse; on liquid crystals and molecular films; papers analyzing the relationship between a violin’s wood and its acoustic properties; comparisons

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In the Beat of a Heart: Life, Energy, and the Unity of Nature between the shapes of water lilies and classical vases; a paper on meteorite craters; another on the mathematical psychology of war, giving equations claiming to calculate the likelihood of conflict; a letter cut out of a newspaper on how much start one would need to outrun a charging elephant (35 yards, apparently the elephant gives up after 200); another cutting on the largest haddock ever landed at Aberdeen; a pamphlet titled “Was Dickens What Is Called a Gentleman?”; and a paper on the musical scale of the highland bagpipe. As I sat in the library, leafing through scrapbooks and piles of correspondence, trying to decipher Thompson’s handwriting—which is just about legible when he is writing to someone else and all but impenetrable when he is making notes for personal consumption, especially as he switches between English, German, French, Latin, and Greek—I realized that I was daft to be hoping to find a thank-you-and-goodnight moment in the jottings of a man who missed his deadlines by decades and whose final work was 10 times longer than originally intended. But, I realized, I was also daft to be looking for a neat ending at all. D’Arcy’s notebooks lift the lid on the stew of ideas, arguments, scenic diversions, lucky accidents, and happy mistakes that were boiled down into On Growth and Form. A similar blend lies behind all scientific work, be it a book, academic paper, or mathematical model. The finished result might look like a tale of serene progress, but it is also an attempt to turn a deaf ear to the clamor of everything left out—all those intriguing, troubling, and inconvenient things trying to force their way back into the picture. Whether people see unity or diversity, solubility or impossibility, says something about them as well as something about the world, and if you choose a different path or a different viewpoint, you will see something different. Why should I expect one conclusion, when every idea is still so contentious and every question throws up so many possible answers? This is not an appeal to relativism, to the idea that all explanations are equally good. The unity of nature might turn out to be a mythical beast, but those hunting it will probably find useful things along the way. If a handful of rules—based, say, on metabolism, genetics, and

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In the Beat of a Heart: Life, Energy, and the Unity of Nature statistics—can explain much of how life works, from molecules to oceans, from forams to quetzals, and explain why life shows both such diversity and such pattern, it will be a stunning achievement. But it won’t be the end. The theories will be there to be challenged, improved, and replaced, and the diversity will still be there to beguile and puzzle. Is nature beautifully simple or beautifully complex? Yes, it is.