Is convergent evolution evidence against common descent?

I think Crash has explained the basics very well. Convergent evolution is really a question of similar biological problems being solved with similar morphological solutions. When similar solutions are arrived at in separate lineages by virtue of independent evolutionary events, there are invariably some detectable differences in those solutions, because the animals don't always play with the same deck, so to speak (they are subject to different evolutionary constraints).Take wings, for example. We KNOW that bird wings and bat wings were produced by completely separate evolutionary events because a bird's wing is contructed exclusively from bones analogous to our arm bones (only derived from their reptilian ancestors). Bats took flight much later and tarsal bones were also modified to support this wing frame structure - bones analogous to our fingers. Two superficially similar, but architecturally different, solutions to the same problem.BAT WING: BIRD WING: Consider now that insects also fly, and their wings have various airfoil shapes reminiscent sometimes of vertebrate wings - and yet they have no bones at all!So convergent evolution is in no way inconsistent with common descent.
On the contrary, it is evidence that we are able to detect when similarities are NOT a function of common descent, i.e. it is evidence that the hypothesis of common descent is falsifiable with respect to particular traits.This message has been edited by EZscience, 06-04-2005 01:47 PMThis message has been edited by EZscience, 06-04-2005 01:48 PM

Yes, the figures weren't the best. I know the bird wing still has digits - they are just not important structural support members of the wing as in the bat (an even worse figure, actually).

An attempt to get the thread back on course...The multiple examples of convergent evolution in nature are testament to the flexibility of the genotype in evolutionary time. At many different times, in many different phyla, evolutionary adaptations converged on similar solutions to similar problem, even though different morphological structures may have been co-opted for the purpose. It is evidence of how powerful directional selection can be, even when working with entirely different genetic blueprints.Convergent evolution says nothing directly for or against commonality of descent, but we could not properly recognize (nor be awe-struck by) the astounding examples of convergent evolution did we not understand the principles of common descent and their inherent constraints.