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Theology in Biology Class: Vestigial Structures as Evidence for Evolution


I was recently reading over the Louisiana science standards, adopted this past March. Those standards include the Louisiana Science Education Act. They contain a provision asking students to “Analyze and interpret scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.”

They further clarify:

Emphasis is on a conceptual understanding of the role each line of evidence (e.g., similarities in DNA sequences, order of appearance of structure during embryological development, cladograms, homologous and vestigial structures, fossil records) demonstrates as related to common ancestry and biological evolution. [Emphasis added.]

Of course, we have talked about public school evolution instruction issues before at Evolution News, but I would like to highlight the issue of vestigial structures.

Arguments for vestigial organs, as presented by Darwin, are metaphysical in nature. Biologist Jonathan Wells has made this point, summarizing the literature:

In 1981, Canadian biologist Steven Scadding argued that although he had no objection to Darwinism, “vestigial organs provide no evidence for evolutionary theory.” The primary reason is that “it is difficult, if not impossible, to unambiguously identify organs totally lacking in function.” Scadding cited the human appendix as an organ previously thought to be vestigial but now known to have a function. Another Canadian biologist, Bruce Naylor, countered that an organ with some function can still be considered vestigial. Furthermore, Naylor argued, “perfectly designed organisms necessitated the existence of a creator,” but “organisms are often something less than perfectly designed” and thus better explained by evolution. Scadding replied: “The entire argument of Darwin and others regarding vestigial organs hinges on their uselessness and inutility.” Otherwise, the argument from vestigiality is nothing more than an argument from homology, and “Darwin treated these arguments separately recognizing that they were in fact independent.” Scadding also objected that Naylor’s “less than perfectly designed” argument was “based on a theological assumption about the nature of God, i.e. that he would not create useless structures. Whatever the validity of this theological claim, it certainly cannot be defended as a scientific statement, and thus should be given no place in a scientific discussion of evolution.”

Logically, to prove a negative in this case — an absence, or a decrease, or loss of something like function — is fraught with difficulty. Hence the reliance on theological speculation, which is out of place in science.

Yet the Louisiana science standards ask teachers to wade into this metaphysically laden topic. In fact, science standards in North Dakota and Utah also mention vestigial structures. There may be other states that do the same.

Indeed, coverage of this topic, likely to be misleading to students, is probably even more widespread that I know. One of the nation’s most prominent high school biology textbooks, by Kenneth Miller and Joseph Levine, talks about vestigiality. It is in a chapter titled “Darwin’s Theory of Evolution”:

Vestigial structures

Not all homologous structures have important functions. Vestigial structures are inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on the descendant. For example, the hipbones of the bottlenose dolphin, shown on page 467, are vestigial structures. In their ancestors, hipbones played a role in terrestrial locomotion. However, as the dolphin lineage adapted to life at sea, this function was lost. Why do dolphins and the organisms in Figure 16-15 retain structures with little or no function? One possibility is that the presence of the structure does not affect an organism’s fitness, and, therefore, natural selection does not act to eliminate it.

Biology class is not the place for metaphysics, or theology. This is a problem, and it needs to be fixed.

Photo: Vestigial structures? You decide. Via Wikicommons.