The Four-Winged Fly
The four-winged fruit fly is a classic example of how creationists misinterpret the genetic analysis of development. Developmental geneticists try to understand the role of a gene by modifying a gene and analyzing the consequences, so it is of little consequence that four winged flies would not survive in the wild. The importance of the four-winged fruit fly is that it demonstrated that a few mutations in a single gene were able to transform an entire structure. This work by Ed Lewis led to the discovery of Hox genes and other members of the genetic toolkit (genes which play roles in constructing animal embryos) as well as to a Nobel Prize in 1996. An inquiry-based textbook might well use Nobel-winning research as a way to encourage inquiry, rather than as a way to obscure critical scientific concepts.
Explore Evolution explains the importance of the four-winged fruit fly by focusing upon the importance of mutations as opposed to the importance of the function of a gene:
These experiments show that mutations can induce dramatic changes in the anatomical structure of organisms. And, for many evolutionary biologists, they provide a powerful confirmation of the neo-Darwinian claim that mutations provide the novel variations that natural selection needs to build new anatomical architectures and animals.Explore Evolution, p. 101
However, as Explore Evolution correctly claims, one cannot assume that natural selection in the wild will operate on the same type of mutations that were artificially selected for in the laboratory:
The neo-Darwinian scenario says that new structures are produced by natural selection acting upon purely undirected and random mutations. Yet, the mutants that produce four-winged fruit flies survive only in a carefully controlled environment and only when skilled researchers meticulously guide their subjects through one non-functional stage after another. This carefully controlled experiment does not tell us much about what undirected mutations can produce in the wild.Explore Evolution, p. 105
No evolutionary biologist would dispute this point.
Have evolutionary biologists been able to actually identify mutations from the wild that cause morphological differences between related species? This work has only recently been undertaken and has already found clear cases in which mutations result in morphological differences between species.
- Mutations in Pitx1 gene affect pelvic hindlimb structure in sticklebacks (Shapiro et al., 2004, Shapiro et al., 2006).
- Mutations in the Ectodysplasin gene affecting armor plates in sticklebacks (Colosimo et al., 2005).
- Mutations in yellow gene affect formation of wing spots in fruit flies (Prud'homme et al., 2006).
- Mutations in shavenbaby affect trichome pattern in fruit flies (Mcgregor et al.,2007).
- Mutations in BMP4 affecting beak morphology in “Darwin’s finches" (Abzhanov et al. 2004).
- Mutations in the KNOT gene in the mustard plant, Arabidopsis, affecting leaf structure(Hay and Tsiantis, 2006).
- Mutations in the Scute gene in fruit flies affecting sensory bristle formation (Marcellini and Simpson, 2006).
These experiments are not meant to show the exact mechanism by which today's biological structures evolution. Laboratory experiments will not perfectly replicate wild conditions, but by considering simpler circumstances, researchers can gain insights into big questions. Lab work like the work described above allows researchers to refine their understanding and move the research to ever-more complex situations, balancing a desire for greater realism for decreased ability to focus on a single factor. Explore Evolution misinforms students about what the research they are describing was meant to show, and misinforms them about the methods of inquiry employed by scientists. This is the opposite of what an inquiry-based textbook should do.