|Wesley R. Elsberry
Joined: May 2002
CH responds: A niche does not cause an adaptation. Adaptations occur via unguided biological variation, such as by mutations. They can then be selected for and become one step in a series of evolutionary changes. Because the biological variation is unguided, there is no target. And since the design space is large and a large number of designs and species are possible, the variation is not likely to repeat. This is why evolutionists are surprised by impressive similarities. Then they explain them as due to similar niches.
Yes, the niche is not the *cause* of adaptation. However, nobody in this argument claimed it was. What you've left off, though, is the fact that the physical constraints that *define* the niche also will be perfectly straightforward explanations for why some changes will be favored (they improved differential reproduction) and others will be disfavored (they decreased differential reproduction). The example of burrowers is one illustrating this, and the example I've used, that of fast swimmers in water adopting a fusiform shape, is another. Changes that produce shape closer to fusiform are *preferred* in organisms that have to move through water quickly, and those that chunkify body shape are *disfavored* in organisms that have to move through water quickly. The fact that the organisms live in the water and try to move quickly doesn't *cause* any particular change to happen, but it *does* give us an independent reason for deriving an expectation for the eventual fate of any such change that does happen.
"You can't teach an old dogma new tricks." - Dorothy Parker