Darwin consistently used the hypothetico-deductive method, Ayala cites examples from Darwin’s work and even uses some of Darwin’s own words, such as “How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service.” Ayala speculates on why Darwin sometimes pretended to be a Baconian inductivist when in fact he mostly practiced what today would be considered modern hypothesis-driven deductive science.
In considering Darwin’s legacy from the current vantage, in Chapter 14 Michael Ruse asks three related questions: Was there a Darwinian revolution? Was there a Darwinian revolution? And, was there a Darwinian revolution? Ruse’s answers to these questions are two resounding yes’s and a qualified yes, respectively. The first resounding yes comes from the fact that after Darwin, rational observers could no longer accept the old picture of humans as somehow the miraculous products of special creation. In other words, the revolution challenged us to rethink dramatically—both emotionally and intellectually—what it means to be human. The second resounding yes comes from the evidence that it was Darwin, rather than his predecessors or contemporaries, who was primarily responsible for the scientific and the metaphysical shifts that society entailed in coming to terms with natural selection’s role in the evolutionary process. The qualified yes comes from the realization that the third question is somewhat philosophical; the answer depends in part on whether to interpret major transformations of thought as continuous and gradual, or discontinuous and abrupt. Ruse discusses philosophical nuances of his own position on these issues.
Natural selection is the key Darwinian concept, and the evolutionary force given top billing in The Origin. But common ancestry is a key concept too, a co-star (albeit not originating strictly with Darwin) of the evolutionary theater. In Chapter 15, Elliott Sober considers how natural selection and common ancestry are related under Darwin’s worldview, and he argues that the latter has a sort of logical (as well as historical) priority over the former. This is because, under Darwinian logic, arguments about natural selection often require the supposition or backdrop of common ancestry (i.e., genealogy and heredity), whereas the logical defense of common ancestry does not require natural selection. In this epistemological sense, Darwin ordered things backward, Sober argues, when he presented natural selection, rather than common ancestry, first and foremost in The Origin. Rather than “evolution by natural selection,” Darwin’s theory might better be described as “common ancestry plus natural selection.”
In Chapter 16, Robert Richards presents a revisionary argument that seems likely to be highly controversial. Using excerpts from Darwin’s writings, Richards makes a case that “Darwin’s theory originally re-infused