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Biogeographic predictability

Explore Evolution asserts "the evidence [from biogeography] is completely consistent with other views of the history of life, in which small-scale changes in form and features do occur within separate but disconnected groups of organisms" (p. 79). In order for a claim to be good science, it is not enough that it be "consistent" with the evidence, it must actually make testable predictions. In the terms stated, this "orchard" model offers no testable predictions, as it is infinitely malleable. It can be adjusted to fit any evidence, but Explore Evolution never offers enough details on the "orchard" to allow any predictions. Given the book's claim to be "inquiry-based," this is at best a sad oversight.

By contrast, the consistency of multiple lines of biogeographic evidence is exactly what would be predicted if all life were evolving in response to the same events throughout earth's history. As discussed above, in standard textbooks, and in the extensive (and uncited by Explore Evolution) scientific literature on biogeography, biogeography generates powerful testable predictions, predictions generated by comparing the biogeography of one group to that of another with shared geography. Biogeographers can predict where new species will be found, and can predict the diversity of communities in areas never before investigated because of the power of biogeography and evolution.

Such tests are impossible for the neo-creationist "orchard" model hinted at by Explore Evolution. The book simply gives too little detail of such a model to allow readers to make any prediction. Since the neo-creationist advocates of this model state forthrightly that they believe that God created each tree in the orchard of life, and since God can do anything, this is a model which is consistent with everything, and predicts nothing. The authors of Explore Evolution, perhaps in order to hide the book's creationist heritage, chose not to explain where they think the many trees of life come from (who planted the "orchard"?), how many trees there are, or why the trees are "separate but disconnected" (who prunes them?). This lack of specificity makes the model potentially consistent with anything, but only because they have chosen to specify nothing.

The "Further Debate" section of this chapter (pp. 79-80) repeats one of the great failings of this text. It highlights two sets of views, presents a weak explanation of one side, anonymous critics on the other, and then simply abandons the students to decide for themselves what to think. The authors might claim that this is consistent with an inquiry-based approach, but as discussed in the critique of chapter 1, this is false. An inquiry-based approach would present a real source of scientific uncertainty (and not a lightly repackaged creationist attack on science) and would provide the students with the tools to investigate the subject further. An inquiry-based textbook would not simply declare "scientists sometimes disagree about how to interpret the various classes of evidence we have examined" (p. 79). That is not inquiry, that is surrender. Scientific inquiry takes disagreement as a starting point for further research, not as a chance to declare that "there may not be much further debate" and "the issue is likely to remain exactly where it is."

Not only does this chapter (and the book as a whole) mislead students about the actual state of scientific knowledge, it misinforms them about the way science works.