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Jan24-12, 10:22 AM
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P: 692
I’m just pointing out Gould’s, Chomsky’s, Turing’s and D’Arcy Thompson’s arguments that mutations and random variations that are viable and helpful are actually highly constrained by physical and chemical laws. So that evolution and natural selection are not synonymous. Natural selection is one process that helps direct evolution—that is, the change over time of groups of organisms—but physical and chemical laws also channel evolution. So when scientists observe some organisms’ traits and see that they’re well fitted to their environments and lifestyles, they are making a leap to assuming that natural selection was responsible for this. Consider these quotes:

It is therefore relevant to ask to what extent examples of adaptive radiation are shaped by natural selection alone rather than being compromised in some way by the processes that generate phenotypic variation. Given that some evolutionary innovation has occurred or some new ecological opportunity has arisen, we can then ask whether the subsequent pulse of elaboration on such a new theme is directed only, or even primarily, by natural selection. Such issues have led to much debate and discussion with numerous examples of potential modes of constraints...

Even in a dramatic example of adaptive radiation, such as Darwin’s finches, the ways in which variation in bill morphology has been generated might influence the morphologies found among the present-day species. In other words, even in the face of the intense natural selection known to occur, at least intermittently, in this system, the forms of bills and other morphological traits might be different from those currently observed if development worked in another way and was based on different genetic pathways and key control points

Patterns of parallel evolution can provide even stronger illustrations of the need to distinguish explanations based on the similarity of natural selection from those involving developmental bias or genetic channeling…Thus, although natural selection in novel environments has no predetermined endpoints, examples of parallel evolution such as in the African cichlids suggest that the ways in which phenotypic variation is generated orchestrate adaptive evolution along certain trajectories.
Evo-devo and constraints on selection