had emerged transformed.
In 1854, having lost the little money that he possessed, and all the specimens that he had collected, in a shipping disaster, an even more deeply impoverished Wallace moved from the Amazon basin to another series of scattered volcanic islands—the Malay Archipelago—on the edge of southeastern Asia. There, like Darwin, he observed astonishing differences between closely related species that had been separated by channels of water. By the winter of 1857, Wallace had begun to formulate a general theory about the mechanism driving variation in these islands. That spring, lying in bed with a hallucinatory fever, he stumbled upon the last missing piece of his theory. He recalled Malthus’s paper. “The answer was clearly . . . [that] the best fitted [variants] live. . . . In this way every part of an animal’s organization could be modified exactly as required.” Even the language of his thoughts—variation, mutation, survival, and selection—bore striking similarities to Darwin’s. Separated by oceans and continents, buffeted by very different intellectual winds, the two men had sailed to the same port.
In June 1858, Wallace sent Darwin a tentative draft of his paper outlining his general theory of evolution by natural selection. Stunned by the similarities between Wallace’s theory and his own, a panicked Darwin dashed his own manuscript off to his old friend Lyell. Cannily, Lyell advised Darwin to have both papers presented simultaneously at the meeting of the Linnean Society that summer so that both Darwin and Wallace could simultaneously be credited for their discoveries. On July 1, 1858, Darwin’s and Wallace’s papers were read back to back and discussed publicly in London. The audience was not particularly enthusiastic about either study. The next May, the president of the society remarked parenthetically that the past year had not yielded any particularly noteworthy discoveries.
Darwin now rushed to finish the monumental opus that he had originally intended to publish with all his findings. In 1859, he contacted the publisher John Murray hesitantly: “I heartily hope that my Book may be sufficiently successful that you may not repent of having undertaken it.” On November 24, 1859, on a wintry Thursday morning, Charles Darwin’s book On the Origin of Species by Means of Natural Selection appeared in bookstores in England, priced at fifteen shillings a copy. Twelve hundred and fifty copies had been printed. As Darwin noted, stunned, “All copies were sold [on the] first day.”
A torrent of ecstatic reviews appeared almost immediately. Even the earliest readers of Origin were aware of the book’s far-reaching implications. “The conclusions announced by Mr. Darwin are such as, if established, would cause a complete revolution in the fundamental doctrines of natural history,” one reviewer wrote. “We imply that his work [is] one of the most important that for a long time past have been given to public.”
Darwin had also fueled his critics. Perhaps wisely, he had been deliberately cagey about the implications of his theory for human evolution: the only line in Origin regarding human descent—“light will be thrown on the origin of man and his history”—might well have been the scientific understatement of the century. But Richard Owen, the fossil taxonomist—Darwin’s frenemy—was quick to discern the philosophical implications of Darwin’s theory. If the descent of species occurred as Darwin suggested, he reasoned, then the implication for human evolution was obvious. “Man might be a transmuted ape”—an idea so deeply repulsive that Owen could not even bear to contemplate it. Darwin had advanced the boldest new theory in biology, Owen wrote, without adequate experimental proof to support it; rather than fruit, he had provided “intellectual husks.” Owen complained (quoting Darwin himself): “One’s imagination must fill up very wide blanks.”
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I. Darwin missed a crucial step here. Variation and natural selection offer cogent explanations of the mechanism by which evolution might occur within a species, but they do not explain the formation of species per se. For a new species to arise, organisms must no longer be able to reproduce viably with each other. This typically occurs when animals are isolated from each other by a physical barrier or another permanent form of isolation, ultimately leading to reproductive incompatibility. We will return to this idea in subsequent pages.
II. Darwin was unsure how these variants were generated, another fact to which we will return in subsequent pages.
The “Very Wide Blank”
Now, I wonder if Mr. Darwin ever took the trouble to think how long it would take to exhaust any given original stock of . . . gemmules . . . It