The Gene: An Intimate History - Siddhartha Mukherjee Page 0,17

1838, in a book by another cleric, the Reverend Thomas Malthus, had nothing to do with divinity.

Thomas Malthus had been a curate at the Okewood Chapel in Surrey by daytime, but he was a closet economist by night. His true passion was the study of populations and growth. In 1798, writing under a pseudonym, Malthus had published an incendiary paper—An Essay on the Principle of Population—in which he had argued that the human population was in constant struggle with its limited resource pool. As the population expanded, Malthus reasoned, its resource pool would be depleted, and competition between individuals would grow severe. A population’s inherent inclination to expand would be severely counterbalanced by the limitations of resources; its natural wont met by natural want. And then potent apocalyptic forces—“sickly seasons, epidemics, pestilence and plague [would] advance in terrific array, and sweep off their thousands and tens of thousands”—leveling the “population with the food of the world.” Those that survived this “natural selection” would restart the grim cycle again—Sisyphus moving from one famine to the next.

In Malthus’s paper, Darwin immediately saw a solution to his quandary. This struggle for survival was the shaping hand. Death was nature’s culler, its grim shaper. “It at once struck me,” he wrote, “that under these circumstances [of natural selection], favourable variations would tend to be preserved and unfavourable ones to be destroyed. The results of this would be the formation of a new species.”I

Darwin now had the skeletal sketch of his master theory. When animals reproduce, they produce variants that differ from the parents.II Individuals within a species are constantly competing for scarce resources. When these resources form a critical bottleneck—during a famine, for instance—a variant better adapted for an environment is “naturally selected.” The best adapted—the “fittest”—survive (the phrase survival of the fittest was borrowed from the Malthusian economist Herbert Spencer). These survivors then reproduce to make more of their kind, thereby driving evolutionary change within a species.

Darwin could almost see the process unfolding on the salty bays of Punta Alta or on the islands of the Galápagos, as if an eons-long film were running on fast-forward, a millennium compressed to a minute. Flocks of finches fed on fruit until their population exploded. A bleak season came upon the island—a rotting monsoon or a parched summer—and fruit supplies dwindled drastically. Somewhere in the vast flock, a variant was born with a grotesque beak capable of cracking seeds. As famine raged through the finch world, this gross-beaked variant survived by feeding on hard seeds. It reproduced, and a new species of finch began to appear. The freak became the norm. As new Malthusian limits were imposed—diseases, famines, parasites—new breeds gained a stronghold, and the population shifted again. Freaks became norms, and norms became extinct. Monster by monster, evolution advanced.

By the winter of 1839, Darwin had assembled the essential outlines of his theory. Over the next few years, he tinkered and fussed obsessively with his ideas—arranging and rearranging “ugly facts” like his fossil specimens, but he never got around to publishing the theory. In 1844, he distilled the crucial parts of his thesis into a 255-page essay and mailed it to his friends to read privately. But he did not bother committing the essay to print. He concentrated, instead, on studying barnacles, writing papers on geology, dissecting sea animals, and tending to his family. His daughter Annie—the eldest, and his favorite—contracted an infection and died, leaving Darwin numb with grief. A brutal, internecine war broke out in the Crimean Peninsula. Men were hauled off to the battlefront and Europe plunged into a depression. It was as if Malthus and the struggle for survival had come alive in the real world.

In the summer of 1855, more than a decade and a half after Darwin had first read Malthus’s essay and crystallized his ideas about speciation, a young naturalist, Alfred Russel Wallace, published a paper in the Annals and Magazine of Natural History that skirted dangerously close to Darwin’s yet-unpublished theory. Wallace and Darwin had emerged from vastly different social and ideological backgrounds. Unlike Darwin—landed cleric, gentleman biologist, and soon to be England’s most lauded natural historian—Wallace had been born to a middle-class family in Monmouthshire. He too had read Malthus’s paper on populations—not in an armchair in his study, but on the hard-back benches of the free library at Leicester (Malthus’s book was widely circulated in intellectual circles in Great Britain). Like Darwin, Wallace had also embarked on a seafaring journey—to Brazil—to collect specimens and fossils and