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discoveries by rivals, and they squabbled against each other almost as much as against Darwinism.
    As these revolutionaries and counterrevolutionaries bitched it out in Europe, the scientist who eventually ended the Darwin-genetics row was working in anonymity in America. Though he mistrusted both Darwinists and geneticists—too much bloviating about theory all around—Thomas Hunt Morgan had developed an interest in heredity after visiting a botanist in Holland in 1900. Hugo de Vries had been one of the trio who rediscovered Mendel that year, and de Vries’s fame in Europe rivaled Darwin’s, partly because de Vries had developed a rival theory for the origin of species. De Vriesian “mutation theory” argued that species went through rare but intense mutation periods, during which the parents produced “sports,” offspring with markedly different traits. De Vries developed mutation theoryafter spotting some anomalous evening primroses in an abandoned potato field near Amsterdam. Some of these sport primroses sported smoother leaves, longer stems, or bigger yellow flowers with more petals. And crucially, primrose sports wouldn’t mate with the old, normal primroses; they seemed to have jumped past them and become a new species. Darwin had rejected evolutionary jumps because he believed that if one sport emerged, it would have to breed with normal individuals, diluting its good qualities. De Vries’s mutation period removed this objection at a stroke: many sports emerged at once, and they could breed only with each other.
    The primrose results scored themselves into Morgan’s brain. That de Vries had no clue how or why mutations appeared mattered not a lick. At last Morgan saw proof of new species emerging, not speculation. After landing a post at Columbia University in New York, Morgan decided to study mutation periods in animals. He began experiments on mice, guinea pigs, and pigeons, but when he discovered how slowly they bred, he took a colleague’s suggestion and tried
Drosophila,
fruit flies.
    Like many New Yorkers then, fruit flies had recently immigrated, in their case arriving on boats with the first banana crops in the 1870s. These exotic yellow fruits, usually wrapped in foil, had sold for ten cents per, and guards in New York stood watch over banana trees to prevent eager mobs from stealing the fruit. But by 1907 bananas and flies were common enough in New York that Morgan’s assistant could catch a whole horde for research simply by slicing up a banana and leaving it on a windowsill to rot.
    Fruit flies proved perfect for Morgan’s work. They bred quickly—one generation every twelve days—and survived on food cheaper than peanuts. They also tolerated claustrophobic Manhattan real estate. Morgan’s lab—the “fly room,” 613 Schermerhorn Hall at Columbia—measured sixteen feet by twenty-three feet and had to accommodate eight desks. But a thousand fruit flies lived happily in a one-quart milk bottle, and Morgan’s shelves were soon lined with the dozens of bottles that (legend has it) his assistants “borrowed” from the student cafeteria and local stoops.

    Thomas Hunt Morgan’s cluttered, squalid fly room at Columbia University. Hundreds of fruit flies swarmed around inside each bottle, surviving on rotten bananas. (The American Philosophical Society)
    Morgan set himself up at the fly room’s central desk. Cockroaches scuttled through his drawers, nibbling rotten fruit, and the room was a cacophony of buzzing, but Morgan stood unperturbed in the middle of all, peering through a jeweler’s loupe, scrutinizing bottle after bottle for de Vries’s mutants. When a bottle produced no interesting specimens, Morgan might squash them with his thumb and smear their guts wherever, often in lab notebooks. Unfortunately for general sanitation, Morgan had many, many flies to smush: although the
Drosophila
bred and bred and bred, he found no sign of sports.
    Meanwhile Morgan got lucky in a different