Darwin's Doubt: The Explosive Origin of Animal Life and the Case for Intelligent Design

by Stephen C. Meyer

In a famous chapter in On the Origin of Species titled “The Mutual Affinities of Organic Beings,” Darwin made his case not on the basis of the fossil evidence, but on the basis of similar anatomical structures in many distinct organisms. He noted, for example, that the forelimbs of frogs, horses, bats, humans, and many other vertebrates exhibited a common five-digit (“pentadactyl”) structure or organization (see Fig. 5.1). To explain such “homologies,” as he called them, Darwin posited a vertebrate ancestor that possessed pentadactyl limbs in rudimentary form. As a menagerie of modern vertebrates evolved from this common ancestor, each retained in its own way the basic pentadactyl mode of organization. For Darwin, his theory of descent with modification from a common ancestor explained these similarities better than the received view of many older nineteenth-century biologists such as Louis Agassiz or Richard Owen, both of whom thought homologies reflected the common design plan of a creative intelligence.