True Gibson

Charles Darwin argued that natural selection produces species analogously to how artificial selection produces breeds. Previous analyses have focused on the formal structure of Darwin’s analogical argument, but few authors have investigated how it is that Darwin’s analogy succeeds in yielding support for his theory in the first place. This topic is particularly salient since at first blush, Darwin's analogical argument appears to undermine the inference he aims to make with it. Darwin held that natural selection produces new species, but artificial selection produces only varieties—a fact which led many of Darwin’s contemporaries to see the analogy as counterevidence to his theory, rather than evidence in favor. I argue that the key to understanding how Darwin’s analogy supports his theory is to recognize three core conceptual revisions to the ‘received view’ of artificial selection for which he argued. Only on Darwin’s resultant ‘revised view’ of artificial selection did his analogical argument support, rather than undermine, his theoretical explanation for the origin of species. These revisions are: (1) the sufficiency of mere differential reproduction for producing evolutionary change; (2) the limitless variation of organisms; and (3) the age and stability of Earth’s geological history. I show why Darwin needed to establish these particular conceptual modifications in order for his analogical argument to generate theoretical support, and I further suggest that accounts focused on the formal aspects of Darwin’s analogy cannot capture the significance of Darwin’s conceptual revisions to the success of his analogical argument.