Free The Reluctant Mr. Darwin by David Quammen

a bright botanist named Joseph Dalton Hooker, just returned from serving as assistant surgeon and naturalist aboard a British ship, the Erebus , on its expedition to Antarctica.
    Darwin had met Hooker passingly back in 1839, before the Erebus sailed, and knew something of this younger man from mutual friends. Hooker knew more about Darwin, having read his Journal , carried it on shipboard for four years, and idolized the scientific traveler who wrote it. Now they connected more personally—though only by mail—in regard to Darwin’s old plant specimens from the Beagle , which had never been properly studied. Despite the chores Hooker faced with his own haul of specimens, he agreed to do it. Darwin asked him to pay special attention to the Galápagos plants, which might bear comparison with the peculiar species of St. Helena, another remote island. That suggestion triggered an outpouring from Hooker about native plants he’d seen on various islands while the Erebus circled the southern oceans, stopping in New Zealand, Tasmania, the Falklands, Hermite Island off Tierra del Fuego, Auckland Island, Campbell Island, Kerguelen, South Shetland, Ascension, and St. Helena itself. Hermite Island, for instance, was rich in mosses. Ascension held eight species of fern, only two of which occurred also on St. Helena, the next island over. Tasmania and New Zealand were unusual in ways of their own. Hooker went on for several pages, his overall message clear: If it’s insular floras you want to talk about, sir, I can oblige you with enthusiasm and data.
    Darwin claimed to be ignorant of botany and waited for Hooker to see the Beagle stuff. Hooker wrote again soon, expressing particular fascination with Darwin’s Galápagos plants, clipped and pressed almost a decade earlier. From having read Darwin’s comments in the Journal , he’d been well prepared to see floral differences among the respective islands, and with the specimens in his hands, that expectation was confirmed. The island-by-island diversity was, in his words, “a most strange fact.” So strange, he volunteered, that it “quite overturns all our preconceived notions of species radiating from a centre.” He meant a center of special creation, presumably on a mainland somewhere. No, the Galápagos plants were flat-out puzzling. Their botanical geography didn’t jibe with the received wisdom of natural theology, and Hooker was willing to say so.
    Darwin perked to that signal. He barely knew Hooker, but suddenly he felt a dawning hope that he had encountered a kindred mind. Hooker was smart and well trained, a conscientious observer; he came from a respectable scientific family (his father was director of the Royal Botanic Gardens at Kew), and had seen as much of the world as Darwin. Yet he was young (only twenty-six) and open to the possibility of junking orthodox tenets if empirical data so dictated. Darwin virtually grabbed him by the lapels. Early in 1844 he wrote again, asking Hooker’s help with “one little fact” about endemic island plants. Then he ended his letter with an impetuous blurt of candor.
    This is a famous moment. It appears in all nine of the Darwin biographies now piled on my desk, plus countless other studies, and it can’t be omitted merely on grounds that the hands of previous writers and scholars have worn it smooth. The letter was undated, but the postmark said January 11, 1844. Darwin confided to Hooker that, besides his interest in southern lands, “I have been now ever since my return engaged in a very presumptuous work,” a work that most people would call downright foolish. He’d been pondering the odd patterns of plant and animal distribution that he had seen in the Galápagos and elsewhere; he’d been reading up on domestic breeding; he’d been collecting every bit of data that seemed relevant to the question of whether species are changeless entities.