NCSE is pleased to offer a free preview (PDF) of Iain McCalman's Darwin's Armada: Four Voyages and the Battle for the Theory of Evolution (W. W. Norton, 2009). The excerpt discusses Alfred Russel Wallace's voyages, culminating with his insight about natural selection: "Whatever it was that triggered Wallace to think about Malthus, it had given him the key to the mechanism that drove evolution. He was not to know that Malthus had done exactly the same for Charles Darwin in 1837-38, when Darwin reread Principle of Population after returning from his Beagle voyage. 'The more I thought it over,' Wallace recalled, 'the more I became convinced that I had at length found the long-sought-for law of nature that solved the problem of the origin of species.' He had found the motor that explained how varieties were driven to become new species, in competition with the parent species that had originally produced them." According to the New York Times Book Review, "[McCalman's] narratives are as much bildungsroman as scientific analysis, showing how the four voyagers were steeled and transformed by the demands of the sea and the wondrous unfamiliarity of life on distant shores."