Elliot Sober: Did Darwin write the Origin of the Species backwards?
On August 10th Elliot Sober spoke about Charles Darwin and his views on The Origin of the Species. Professor Sober is the Hans Reichenbach Professor and the William F. Vilas Research professor at the University of Wisconsin-Madison. Dr. Sober discussed how Darwin’s theory centered on natural selection and common ancestry. Natural selection is an important force that contributes to evolution, while common ancestry is the idea that all species alive today come from one to a few original progenitors. Sober’s presentation focused on the first chapter of his 2011 book Did Darwin Write the Origin Backwards, and examined how natural selection and common ancestry relate to one another.
Sober questioned why, in The Origin of the Species, did Darwin organize his book by beginning with natural selection and its importance, but then later in the book defend the theory of common ancestry. Sober’s main interest was how these two parts of the theory of evolution fit together, the relation between them, and the evidence that supports each.
Dr. Sober asserted that you can obtain ample amounts of evidence for common ancestry, even if natural selection never caused any characteristics to evolve. For example, Sober relates how Darwin researched skull sutures that are present in mammals, but also in birds and reptiles. In mammals, skull sutures help facilitate live birth, making the process easier. However, with birds and reptiles skull sutures do not serve the same function since birds and reptiles hatch from eggs. As such, Darwin hypothesized that they shared a common ancestor and the presence of skull sutures in birds and reptiles is evidence of that common ancestry and not natural selection. Sober suggested that this is some indication that common ancestry is evidentially prior to natural selection in The Origin.
Given the evidential priority of common ancestry, Sober considered three hypotheses about why Darwin started with natural selection. First of all, it could be that Darwin believed natural selection was more novel and exciting. On the other hand, it might also be the case that his readers would rebel against the idea that human beings and monkeys shared a common ancestor. However, Sober argued that Darwin thought natural selection should be first due to causal priority insofar as natural selection causes extinction pruning the tree of life.
Professor Sober ended his presentation by examining his question, did Darwin write the origin backwards, and he answered that by stating causally, the book is in the right order but evidentially, the book is backwards.