Evolution Icon Evolution

Strickberger’s Evolution Textbook Promotes False Evolutionary Icons

Robert F. Shedinger
Photo credit: Ben Sale, via Flickr (cropped).

Editor’s note: Dr. Shedinger is a Professor of Religion at Luther College in Decorah, Iowa. He is the author of a recent book critiquing Darwinian triumphalism, The Mystery of Evolutionary Mechanisms. See also the earlier entries in this series:

Twenty years ago, Jonathan Wells published one of the seminal books of the intelligent design movement, Icons of Evolution. Wells demonstrated how biology textbooks perpetuate a standard set of ideas and images purporting to support Darwinian evolution even though these iconic ideas and images are far more ambiguous than the textbooks portray. Here I will consider the appearance of some of these icons in Strickberger’s Evolution textbook, as edited and updated by Brian K. Hall and Benedikt Hallgrimsson, which I have been reviewing.

Rather than being grouped together in a chapter regarding evidence for evolution, the icons are scattered about and appear in discussions of issues that they are said to illustrate or illuminate in some way. For example, Darwin’s Finches appear in a chapter about Charles Darwin, with the famous work by Peter and Rosemary Grant being relegated to a peripheral text box. Here we learn that the Grants have shown how “Natural selection can produce evolutionary change very rapidly but that the direction of selection in particular populations can change frequently and unpredictably as environmental conditions fluctuate.” This is an accurate summary of the Grants’ work, yet Hall and Hallgrimsson can’t leave well enough alone. They feel compelled to continue:

By documenting evolution in action in natural populations, the work of the Grants has made profound contributions to our understanding of the evolutionary process.

Actually, by documenting the oscillating nature of the changes in finch beaks, the Grants have demonstrated that natural selection has the power to produce only small-scale adaptations, a process that says little about larger evolutionary processes and trends.

Haeckel’s Embryos

We turn next to Ernst Haeckel’s famous embryo drawings. In a section on embryology, Strickberger’s Evolution reproduces Haeckel’s iconic drawings showing various vertebrate embryos in three stages of development. In an accompanying caption we read, “Although Haeckel took some liberties in drawing these figures, the earlier stages are more similar to one another.” If Haeckel took liberties in his drawings, then how do we know that the earlier stages really do look more similar? Perhaps Haeckel made them look more similar than they actually do. Why are these more than century-old drawings even in the textbook instead of modern digital photographs of embryos?

We do know today that Haeckel’s earlier stage of development is actually a later stage, and that embryos look quite different in their true earlier stage. But the textbook ignores this important information. Moreover, Hall and Hallgrimsson have deftly dropped in a reference to the appearance of “pharyngeal (gill) arches” in the earlier stage of the embryos. The modern terminology “pharyngeal arches” is correct, but placing gill in parentheses subtly perpetuates the discredited idea that embryos of terrestrial vertebrates bear the marks of marine ancestors. 

Fruit Flies and Gene Regulation

Next, in a section on gene regulation, we find the familiar image of the four-winged fruit fly. In the surrounding text, we learn that mutations in regulatory genes that govern development probably play a significant role in evolution since they can alter the development of entire parts of an organism. The iconic example of this is, of course, the fruit fly that undergoes a mutation that “converts the abdominal segment into a thoracic segment and abdominal appendages (halteres) into thoracic appendages (wings).” Therefore:

…there are compelling reasons for the view that mutations in regulatory genes are of great importance in evolution.

Nowhere in this discussion is it ever mentioned that the mutant fruit flies’ extra pair of wings are nonfunctional. Far from being a useful evolutionary adaptation, they render the fly a cripple and therefore an evolutionary dead end. This is why all the fruit flies currently buzzing around the bananas in my kitchen have only one pair of wings! 

The Most Pervasive Icon of All

From crippled fruit flies we move to perhaps the most pervasive icon of them all, the peppered moth. Introduced in a section titled “Polymorphism and Industrial Melanism,” a basic error of definition is made when Hall and Hallgrimsson write, “Certain moths and butterflies show increased proportions of dark-colored compared to melanic forms…” Of course, melanic forms are the dark-colored ones! 

Next, we are introduced to the experimental work of Bernard Kettlewell, which we are told showed industrial melanism to be an example of natural selection in action driven by differential bird predation:

The relative fitness of the melanic types may lie, at least partly, in their ability to remain concealed from bird predators on darkened twigs or tree trunks.

We now know that peppered moths in the wild do not rest by day on tree trunks but on horizontal branches high in the canopy where they are hidden by leaves, no matter their color. Kettlewell’s experiments did not replicate the experience of moths in the wild and his work has been harshly criticized on a number of methodological grounds. 

Interestingly, we read in an accompanying footnote, “See Brakefield (1998) and Majerus (1998) for melanism, and see Hooper (2002) for the history of research on the peppered moth.” Majerus (1998) is a reference to Michael Majerus’s book on industrial melanism that actually lays out in great detail all the methodological problems with Kettlewell’s experiments. In fact, it was the reading of Majerus’s book that led well-known Darwinian biologist Jerry Coyne to admit the embarrassment he felt about teaching the standard peppered moth story to students for years, not realizing the problems with it. He likens his reaction to the shock he experienced as a child when he learned that it was his father, not Santa, who brought the presents at Christmas!

Hooper (2002) refers to science writer Judith Hooper’s book Of Moths and Men: Intrigue, Tragedy, and the Peppered Moth. Hooper’s book came under considerable criticism: by Coyne for downplaying the significance of industrial melanism as an example of natural selection, and by Majerus for its character assassination of moth specialists. 

Considering Majerus’s criticism of Kettlewell, and Coyne and Majerus’s criticism of Hooper, one must wonder if Hall and Hallgrimsson even know the contents of the books they cite. If they had read Majerus, they never could have written what they did about Kettlewell. 

In a caption below a picture showing birds eyeing dark and light-colored moths on a polluted tree trunk, we find this startling passage:

Although trees are commonly shown as resting sites for these moths, their actual habits are unknown. Some evolutionary biologists suggest caution in crediting color camouflage as the full explanation for Biston betularia polymorphism.

This is essentially correct, but it contradicts the accompanying picture showing birds eyeing moths on tree trunks! A picture is worth a thousand words, and few students will read the caption. This allows Hall and Hallgrimsson to claim that they are not misrepresenting the ambiguity here, but the attempt is disingenuous at best. Besides, this caption also contradicts what they have said about Kettlewell in the main text. It is clear what they want students to take away from the peppered moth story.

Additionally, Strickberger’s Evolution fails to mention the work of G. T. Porritt, who in 1907 noted the invasion of dark-colored moths into pristine woodlands where they thrived. This is completely contrary to what natural selection should produce. Industrial melanism is indeed a complex process not clearly explainable by natural selection. But you would never know this from the textbook. 

A Final Icon

One final icon referenced by Strickberger’s Evolution is junk DNA (included in Wells’s follow-up book Zombie Science). Hall and Hallgrimsson note that 97 percent of human DNA is non-coding and may be referred to as junk. But we know from the ENCODE project that much of this “junk” may have important regulatory functions, a prediction actually made by intelligent design advocates. 

It is clear that in updating Strickberger’s Evolution, Hall and Hallgrimsson did not want to place all the icons of evolution together in a chapter on evidence for evolution, recognizing the problematic nature of many of these icons. Yet it also clear that they still wanted to include them while downplaying their problematic nature. In short, the attempt is disingenuous. Students deserve the full picture, warts and all.