Doubting Common Ancestry

Explore Evolution claims that some people who doubt common ancestry accept fixity of species, so biogeography doesn't prove anything to them. One such 19th century scientist:

accepted that migration and adaptation would alter the features of species. Nevertheless, he doubted that species could undergo unlimited change, and did not accept that all species shared a common ancestor. Many modern critics of neo-Darwinism share this view.
Explore Evolution, p. 78

Cuvier shares little with the modern creationists he is being compared with here. Cuvier wrote in the early 19th century, decades before Darwin and Wallace, and the understanding of genetics and the fossil record which Darwin had, let alone which modern scientists enjoy. He can be excused for thinking species appeared from some unknown source and remained fixed in form thereafter. If this is the most recent genuine scientist Explore Evolution can cite who holds this view, it is hardly a ringing endorsement. Cuvier's claims had there day, but research in his day and since then have falsified his views.

This small aside at the chapter's end takes back the small concession to critics of creationism offered at the chapter's beginning. Before, the authors acknowledge that species fixity "isn't even a blip on the radar" today. But again, biogeography is not simply an exercise in disputing species fixity: it demonstrates that taxonomic ranks above the species level are not fixed, and shows the process by which species diversify, and by which the branching process of evolution has produced those higher taxonomic levels.

Nor is biogeography simply concerned with speciation and adaptive radiation (a process the authors denigrate in the following chapter). Biogeography shows a great deal more than that species can change. Even within the limited subset of biogeography that Explore Evolution chooses to address (adaptive radiation), there is clear evidence for evolution of new species, genera, families, etc., and illustrations of the power of evolution to produce morphological novelty with great speed, given the right conditions. This is exactly the opposite conclusion from the one Explore Evolution draws. That does not mean that a debate is underway, only that the selective use of evidence can produce misleading results. When this book declares it impossible for evolution to accomplish a task, and then ignores instances where evolution does explain how that impossible thing happened, it calls the book's credibility, not evolution's, into question.

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