Reading The Extended Phenotype, Richard Dawkins....

and he said something on page 3 that I don't get. His thought experiment: Can an ant evolve into a red-tailed deer? His answer is "Yes", because (paraphrasing) all we need to do is exhibit a sequence of nearly-identical animals leading from the ant to the deer. You get this sequence by going up the evolutionary tree from the ant to the common ancestor, then back down to the deer.

Then he says the iffy thing: presumably the right set of environmental pressures can be applied to produce this sequence of evolutionary steps. So any animal can evolve into any other. He claims this is so unlikely it will never happen, but it's possible.

Huh? Take genotype A and genotype B, differing only by a mutation. Just because the comparative fitness of A against B depends on the environment, that doesn't mean there have to be two distinct environmental regimes - one where A is better, and another where B is better. There doesn't seem to be any a priori reason to think that, but it's necessary for his statement of reversability to be true.

Maybe things will get cleared up by page 5....

- posted by Scott @ 8:32 AM