During my recent trip to the Creation Museum I picked up a copy of David DeWitt’s book Unraveling the Origins Controversy. DeWitt is the Director of the Center for Creation Studies at Liberty University. It’s been a while since I’ve read an actual YEC book, and I was growing nostalgic for the experience.
And wouldn’t you know it! Almost as soon as DeWitt turns from religious questions to scientific ones, the quote-mining begins. Consider this:
Often the evidence that is used to support common ancestry is the similarities between organisms. Mayr explained:
Since all members of a taxon must consist of the descendants of the nearest common ancestor, this common descent can be inferred only by the study of their homologous characters. But how do we determine whether or not the characters of two speices are homologous? We say that they are if they conform to the definition of homologous: A feature in two or more taxa is homologous when it is derived from the same (or a corresponding) feature of their nearest common ancestor. (Emphasis in Original).
Or consider this from a recent biology textbook:
Similar structures in two or more species are called homologous structures if the structures are similar because they evolved form the same ancestral structure.
Notice the circular reasoning that is being applied here. Common ancestry is inferred by studying homologous (similar) characters and yet homologous characters are defined as being derived from a common ancestor. This becomes extremely problematic and only works if you assume that common ancestry is true. (pp. 100-101) (Emphasis in Original)
Circular reasoning? That second quotation doesn’t seem to have any reasoning at all. It merely defines a technical term.
But it’s that Mayr quote I want to focus on. You’ll find it on page 16 of his book What Evolution Is. It appears in a lengthy chapter describing some of the evidence for common descent. Curiously, though, it does not appear in the portion of the chapter describing how morphological similarities (between the forelimbs of various mammals, for example) provides evidence for descent. It is actually in a section on the fossil record.
DeWitt began the Mayr quote with the second sentence of the paragraph. The first sentence is this:
The study of phylogeny is really a study of homologous characters.
We then have the quote as presented by DeWitt, followed by this:
This definition applies equally to structural, physilogical, molecular, and behavioral characteristics of organsims. But how are we to determine whether homology is substantiated in a particular case? Fortunately, there are numerous criteria (see Mayr and Ashlock 1991). For structures this includes the position in relation to neighboring structures or organs; by connecting two dissimilar features by intermediate stages in ancestors; by similarity in ontogeny; and by intermediate fossils. The best evidence for homology has been provided in recent years in molecular biology.
There follows several more sentences elaborating on this.
Gives rather a different impression from DeWitt, wouldn’t you say? Is Mayr inferring common descent from homologous characters, and then defining homologous characters as those that arise from common descent? Of course not. He’s pausing a discussion on the importance of the fossil record to describe briefly some practical issues that arise in trying to recreate specific lines of descent. Mayr does, in fact, provide a discussion of how certain patterns of similarities and differences across organisms provides further evidence of common descent, but you will find that discussion elsewhere (on pages 22-27, to be exact).
Ah, creationist sleaze. How I’ve missed you.