The island of Ternate is a small, graceful volcanic cone rising leafy green from the sea in northeastern Indonesia, 600 miles east of Borneo. Although it's an out-of-the-way place, tucked between much larger islands, Ternate was once an entrepôt of the Dutch empire, from which spices and other precious tropical commodities traveled westward by ship. Today its busy dock area, its fruit and fish markets, its mosques, its old forts, its sultan's palace, and its tidy concrete houses are strung like carousel lights along a single ring road that traces the coastline. Its upland slopes are mostly forested and unpopulated, and in those woods, if you're lucky, you might still spot a certain resplendent bird, emerald-breasted, with two long white plumes dangling capelike from each shoulder, whose scientific name—Semioptera wallacii—honors the man who first brought it to scientific attention. That man was Alfred Russel Wallace, a young English naturalist who did fieldwork throughout the Malay Archipelago in the late 1850s and early '60s. What you won't see on Ternate is any grand plaque or statue commemorating Wallace's place in scientific history or the fact that, from this little island, on March 9, 1858, he sent off a highly consequential letter, aboard a Dutch mail steamer headed westward.
The letter was addressed to Mr. Charles Darwin. Along with it Wallace enclosed a brief paper titled "On the Tendency of Varieties to depart indefinitely from the Original Type." It was the product of two nights' hasty scribbling, which followed a moment's epiphany during a fever, which in turn followed more than ten years of speculation and careful research. What the paper described was a theory of evolution (though not under that name) by natural selection (not using that phrase) remarkably similar to the theory that Darwin himself, then an eminent naturalist of rather conventional reputation, had developed but hadn't yet published.