Modeling Cultural Evolution

When Darwin left for his voyage around the world on the Beagle, he took with him the first volume of Charles Lyell’s Principles of Geology. Later in the voyage he received the second volume by post somewhere in South America. Lyell never accepted Darwin’s account of evolution by natural selection, presumably because of his religious beliefs. It is ironic then that Lyell’s work played a crucial role in the development of Darwin’s thinking. In some ways Lyell’s principle of uniformitarianism is as central to Darwinism as is natural selection. Before Lyell, it was common to explain the features of the earth’s geology in terms of past catastrophes: floods, earthquakes and other cataclysms. In contrast, Lyell tried to explain what he observed in terms of the cumulative action of processes that we could observe every day in the world around us—the sinking of lands and the build up of sediments. By appreciating the accumulated small effects of such processes over long time spans, great changes could be explained. Darwin took the idea of small changes over long time spans and applied it to populations of organisms. Darwin was a good naturalist and knew a lot about the everyday lives of plants and animals. They mate, they reproduce, they move from one place to another, and they die. Darwin’s insight was to see that organisms vary, and the processes of their lives affect which types spread and which diminish. The key to explaining long run change in nature, to explaining the origin of new species, of whole new types of organisms, and of life itself was to apply Lyell’s principle of uniformitarianism to populations. By keeping track of how the small events of everyday life change the composition of populations, we can explain great events over long time scales.