Monday, September 16, 2013

Biogeographic evidence for evolution

I'm going to quote from a standard evolutionary textbook, citing one standard line of evidence for evolution. D. Futuyama, Evolution (Sinaur 2005).

If someone asks us why there are no elephants in the Hawaiian Islands, we will naturally answer that elephants couldn't get there. This assumes that elephants originated somewhere else: namely, on a continent. But in a pre-evolutionary worldview, the view of special divine creation that Darwin and Wallace were combating, such an answer would not hold: the Creator could have placed each species anywhere, or in many places at the  same time. In fact, it would have been reasonable to expect the Creator to place a species wherever its habitat, such as rain forest, occurred (118).

i) Notice that this is a theological argument rather than a scientific argument against special creation. 

ii) Darwin and Futuyama assume, rather than demonstrate, that if God made all the natural kinds by special creation, then all the same kinds of ecological zones would contain all the same kinds of organisms. That's a key assumption, and that's quite an assumption. Moreover, it's dubious to claim that a pre-evolutionary worldview fosters that expectation. To the contrary, major Christian thinkers like Augustine, Aquinas, and Leibniz espoused the principle of plenitude, according to which God will create a world with maximal diversity. On that assumption, we wouldn't expect rote repetition of the same "species" in the same habitats. Rather, we'd expect variation. The greater the better. 

Similar climates and habitats, such as deserts and rain forests, occur in both the Old and the New World, yet organisms inhabiting them are unrelated…Darwin's second point is that "barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions [organisms] of various regions." Darwin noted, for instance, that marine species on the eastern and western coasts of South America are very different (118-119).
Darwin's "third great fact" is that inhabitants of the same continent or the same sea are related, although the species themselves differ from place to place. He cited as an example the aquatic rodents of South America (the coypu and capybara), which are structurally similar to, and related to, South American rodents of the mountains and grasslands, not to the aquatic rodents (beaver, muskrat) of the Northern Hemisphere (119).

It's hard to see how that's an argument against special creation. There seems to be a missing premise. It only makes sense on the assumption that special creation entails the fixity of the species. 

That, however, is not an implication of special creation. Fiat creationists (as well as progressive creationists) have no problem admitting that populations in geographically or ecologically isolated areas adapt to their distinctive habitat, becoming more specialized, more like their counterparts in the same vicinity, and less like their counterparts across natural barriers. Put another way, fiat creationism opposes macroevolution, not microevolution. Natural kinds can change, within limits. 

For Darwin, it was important to show that a species had not been created in different places, but had a single region of origin. He drew particularly compelling evidence from the inhabitants of islands. First, distinct oceanic islands generally have precisely those kinds of organisms that have a capacity for long-distance dispersal and lack those that do not. For example, the only native mammals on many islands are bats. Second, many continental species of plants and animals have flourished on oceanic islands to which humans have transported them. Thus, said Darwin, "He who admits the doctrine of the creation of each separate species, will have to admit that a sufficient number of the best adapted plants and animals were not created for oceanic islands" (119).
Third, most of the species on islands are clearly related to species on the nearest mainland, implying that that was their source. This is the case, as Darwin said, for almost all the birds and plants on the Galapagos Islands. Fourth, the proportion of endemic species on an island is particularly high when the opportunity for dispersal to the island is low. Fifth, island species often bear marks of their continental ancestry (119).

These objections seem to combine the two aforesaid assumptions: fixity of species and God populating the same ecological zones with the same set of organisms. 

So the biogeographic evidence for evolution boils down to two arguments. And both arguments are predicated on false premises. It's striking that both Darwin and Futuyama imagine that's inconsistent with special creation.  It reflects a hidebound understanding of special creation. Their objections are illogical and ignorant. 

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