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N.Wells



Posts: 844
Joined: Oct. 2005

(Permalink) Posted: Feb. 12 2007,20:01   

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But how can I use this to argue that homologies are powerful evidence? For instance, your comparison of insect flight with bird/bat flight fails. The Reynolds number difference alone renders the comparison problematic, but there are other issues as well. I have never built a bird or a bat, and so I do not have a good understanding of how arbitrary are their wing designs, but the idea insect wing design reveals that bird wing design is arbitrary is erroneous.

As someone else noted, the Reynold's number difference is more of a red herring than anything else.  (For example, the group of "flying insects" includes a dragonfly with a 6 ft wingspan.)  More importantly, all these flying groups exist, but each group maintains its own unique innovations. Whatever differences you come up with in how the different groups fly will be trumped by the existence of flightless birds, like ostriches and flightless rails, that still maintain basic bird hand-and-wing construction.

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And you run into more problems with your appeal to genetic and biochemical character traits. These present incongruities all over the map. And your appeal to development pathways and genes is yet another problem for the evolutionary homology argument. Often homologies arise from different pathways and genes.

Those sorts of things pose difficulties, but not insuperable problems.  If all those separate things align, then homology is hard to refute.  If they fail to align and a biologist still thinks the features are homologous (which can happen), then the biologist needs some fancy evidence to support that claim.  If you, CH, want to dispute homology then you have to demonstrate that biochemistry, DNA, developmental histories, and nested hierarchies involving minor nonfunctional features can be achieved other than by common descent.

  
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