Vertebrate limbs - Vertebrate limbs Summary of problems:...

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Vertebrate limbs Summary of problems: Common function can explain certain similarities of form, but cannot explain similar developmental pathways, or the particular components that make up certain structures in different species. Full discussion: The discussion of functional constraints in Explore Evolution is nearly impossible to state in a way which does not refute itself. They do not deny the remarkable similarity between the structures of species within various taxonomic groups. They do not deny that one can produce a hierarchal (branching) arrangement of the ways these structures vary within and among these groups, and that the branching pattern is consistent regardless of which particular structure you examine. In other words, their response to the evidence of the branching pattern predicted by the tree of life is to agree that it is all accurate. They simply argue that it is possible to invoke special explanations for each such structure, multiplying causes needlessly. This practice violates basic scientific and logical principles. By treating structures in isolation, they obscure the actual evidence examined by scientists. For instance, EE cites biologists from 150 years ago, biologists whose arguments were tested and found lacking. Agassiz, for example, explained homologies as the result of the necessity of using similar structures to solve similar functional problems. On this view, the pattern we see in the vertebrate forelimb — a single bone closest to the trunk, two bones in the next segment, and a variety of bones in the segment farthest out — exists for important functional reasons. It is worth noting, to begin with, that vertebrate limbs do not have "a variety of bones in the
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Vertebrate limbs - Vertebrate limbs Summary of problems:...

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