AbstractThough Darwin had formulated his theory of evolution by natural selection by early fall of 1837, he did not publish it until 1859 in theOrigin of Species. Darwin thus delayed publicly revealing his theory for some twenty years. Why did he wait so long? Initially this may not seem an important or interesting question, but many historians have so regarded it. They have developed a variety of historiographically different explanations. This essay considers these several explanations, though with a larger purpose in mind: to suggest what makes for interesting problems in history of science and what kinds of historiographic models will best handle them.