The Nature of Change: Evolutionary mechanisms give rise to basic structural differences

Without defining “design,” Wells asserts that “many features of living things appear to be designed.” Then he contrasts natural selection (undirected) with design (directed), apparently attempting to return to the pre-Darwinian notion that a Designer is directly responsible for the fit of organisms to their environments. Darwin proposed a scientific rather than a religious explanation: the fit between organisms and environments is the result of natural selection. Like all scientific explanations, his relies on natural causation.

Modern science can now draw on evidence from biological processes.

Wells contends that “Darwin’s theory cannot account for all features of living things,” but then, it doesn’t have to. Today scientists explain features of living things by invoking not only natural selection but also additional biological processes that Darwin didn’t know about, including gene transfer, symbiosis, chromosomal rearrangement, and the action of regulator genes. Contrary to what Wells maintains, evolutionary theory is not inadequate. It fits the evidence just fine.

Darwin’s conclusion that Galápagos finches had a common ancestor is confirmed by modern genetic analysis.

Reading Wells, one might not realize the importance of the Grants’ careful studies, which demonstrated natural selection in real time. That the drought conditions abated before biologists witnessed the emergence of new species is hardly relevant; beak size does oscillate in the short term, but given a long-term trend in climate change, a major change in average size can be expected. Wells also overstates the importance of finch hybridization: it is extremely rare, and it might even be contributing to new speciation. The Galápagos finches remain a marvelous example of the principle of adaptive radiation. The various species, which differ morphologically, occupy different adaptive niches. Darwin’s explanation was that they all evolved from a common ancestral species, and modern genetic analysis provides confirming evidence.

The discovery of _Ubx_ genes shed light on how body plans evolve.

Wells admits that natural selection can operate on a population and correctly looks to genetics to account for the kind of variation that can lead to “new features in new species.” But he contends that mutations such as those that yield four-winged fruit flies do not produce the sorts of anatomical changes needed for major evolutionary change. Can’t he see past the example to the principle? That the first demonstration of a powerful genetic mechanism happened to be a nonflying fly is irrelevant. Edward Lewis shared a Nobel Prize for the discovery of the role of these genes, known as the Ubx complex. They are of extraordinary importance because genes of this type help explain body plans — the basic structural differences between a mollusk and a mosquito, a sponge and a spider.

A very small _Ubx_ change results in a big difference in the body plan of organisms.

Ubx genes are among the HOX genes, found in animals as different as sponges, fruit flies, and mammals. They turn on or off the genes involved in — among other things — body segmentation and the production of appendages such as antennae, legs, and wings. What specifically gets built depends on other, downstream genes. The diverse body plans of arthropods (insects, crustaceans, arachnids) are variations on segmentation and appendage themes, variations that appear to be the result of changes in HOX genes. Recent research shows that fly Ubx genes suppress leg formation in abdominal segments but that crustacean Ubx genes don’t; a very small Ubx change results in a big difference in body plan.

These genes allow for anatomical experimentation.

Mutations in these primary on/off switches are involved in such phenomena as the loss of legs in snakes, the change from lobe fins to hands, and the origin of jaws in vertebrates.HOX-initiated segment duplication allows for anatomical experimentation, and natural selection winnows the result. “Evo-Devo” — the study of evolution and development — is a hot new biological research area, but Wells implies that all it has produced is crippled fruit flies.

Science only has tools for explaining things in terms of natural causes.

Wells argues that natural explanations are inadequate and, thus, that “students should also be taught that design remains a possibility.” Because in his logic, design implies a Designer, he is in effect recommending that science allow for nonnatural causation. We actually do have solid natural explanations to work with, but even if we didn’t, science only has tools for explaining things in terms of natural causation. That’s what Darwin did, and that’s what we’re trying to do today.