Eventually, of course, Darwin devised a theory—survival of the fittest, as we commonly know it; descent with modification, as he called it—that explained the wondrous complexity of living things in a way that didn’t require the intervention of a deity at all. In 1842, six years after the end of his voyage, he sketched out a 230-page summary outlining the theory’s principal elements. Then he did an extraordinary thing: he locked it away in a drawer and kept it there for the next sixteen years. The subject, he felt, was too hot for public discussion.
