On the Monday holiday, I was working on my lecture for Tuesday. I’m teaching plant diversity this semester, and in the early lectures of the course I like to discuss concepts and intellectual tools that we will use throughout the semester. The concepts and tools I introduce are important in comparative biology—that is, they help us to compare one kind of organism to another as we work to explain diversity.
After discussing familiar ideas of classification in the first lecture, I moved on to basic ideas of phylogeny reconstruction—how we infer evolutionary relationships—in the second lecture. My theme for Tuesday was homology, which is one of my favorite topics. Homology is basically a proposal of equivalence. If we say that the arm of a human, the arm of a chimpanzee, and the wing of a bird are homologous, then we are hypothesizing that these corresponding structures are somehow equivalent. The somehow of that equivalence is what a biologist wants to explore and to explain. In a facile manner, I could say that homology of the arm of a human, the arm of a chimpanzee, and the wing of a bird is explained because they are all modifications of a corresponding structure in their most recent common ancestor, which is to say that we have homology because of evolution.
A less facile explanation would require us to explain how common position within bodies and possible similarities in development, including perhaps similar genes being expressed to control development, of humans, chimpanzees, and birds lead to a hypothesis of homology. We might also be expected to explain how intermediate structures in the lineages ‘between’ humans and chimpanzees as well as between them and birds help to demonstrate the transformations that could have occurred since their divergence from a common ancestor. Formulating this set of explanations to propose an hypothesis of homology is sometimes called a ‘homology argument.’
As I wrote my lecture on Monday, I wanted to look for new examples of homology arguments—so I googled ‘homology argument.’ One of the top links that Google returned in the search was for an entry in the Conservapedia, which subtitles itself as “The Trustworthy Encyclopedia.” The link took me to the Conservapedia entry for homology, which it defined as “. . . the theory that macroevolutionary relationships can be demonstrated by the similarity in the anatomy and physiology of different animals.” While I don’t regard that definition as accurate, it’s neither egregious nor exactly untruthful.
It was the section below the Conservapedia’s definition of homology that caught my attention—it was labelled “Invalidity of the Homology Argument.” How could the homology argument be invalid, I wondered? After all, a homology argument is a method of comparing and reasoning rather than an assertion of truth.
The explanation offered by the Conservapedia for the invalidity of the homology argument is straightforward: “Creation scientists claim that similarity can just as readily be explained by a common Designer as common ancestry, and that homology is therefore not evidence that can be used to support the evolutionary view.”
The statement is very interesting, and like most creationist arguments relies more on rhetoric than on knowledge. It is true that many creationists claim that a ‘designer’ is responsible for the diversity of life; however, that claim is not supported by evidence from any tests of the origins of biological diversity. All the Conservapedia statement really says is that a ‘claim’ by creation scientists means that homology is not evidence useful to support evolution. Why would anyone make such an enormous assumption about homology and evolution based on a ‘claim’?
All that seemed to matter to the Conservapedia were dismissals offered by creationists. The entry suggested that the invalidity of homology arguments was further ‘supported’ by the following quote from J. P. Holding: “To frame our argument against the evolutionists’ misuse of homologous structures requires us to have an understanding of certain values critical to ancient persons. Roman literature of the New Testament period tells us that ‘(t)he primary test of truth in religious matters was custom and tradition, the practices of the ancients.’ In other words, old was good, and innovation was bad. Change or novelty was ‘a means value which serves to innovate or subvert core and secondary values.’”
This was excellent stuff, and I decided to use it in my lecture on homology. [I note that conservatives complain frequently that their ideas are ignored in academia so I felt especially good about introducing the Conservapedia and its claims in my class.]
We discussed in class a critical difference between a scientist and a creationist. Creationists think they have THE answer from the beginning, whereas a scientist has only a question in the beginning. While a creationist may accept absurd dogma and simplistic dismissals of rational ideas, a scientist looks for a way to test ideas. That willingness to test and to infer from the results of those tests the best explanations distinguishes the scientific method from the creationist method. [A great untruth of the Conservapedia’s entry on homology was its claim that there are creation ‘scientists’—creationists offer religious explanations and dismiss the results of repeatable scientific studies rather than using a scientific method.]
The Conservapedia quotation from Holding was especially interesting in stating that we are required to “have an understanding of certain values critical to ancient persons” to understand why homology arguments are invalid. It is unclear to me how knowledge of values invalidates a scientific method. Indeed, a strength of the scientific method is that it is not contaminated by values (while we can all recognize that individual scientists and others may be influenced by values). How can custom and tradition invalidate homology arguments?
The Conservapedia entry on homology seems more concerned with acceptance of “custom and tradition” as a basis for “truth of religious matters” than with possible comparisons we might make among organisms. Indeed, it seems that the Conservapedia aims to dismiss important scientific approaches through superficial allusions. Perhaps we should be wary of trusting the Conservapedia, despite its subtitle.
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Quotes are taken from the Conservapedia at http://www.conservapedia.com/Homology.