Hi AC: Welcome to the forum. It's a pleasure to see postings by a creationist who isn't simply either hit-and-run or who merely wishes to "witness" to the heathen.
Reply: The concept of convergence is most definitely a problem for evolution via random mutations, simply because of the very fact that all of these instances of parallel evolution must have had fortuitously similar mutations occurring independently from one another. And since mutation is random, the development of major morphological/physiological characteristics multiple times is not what one would expect.
You also stated in an earlier post that, convergence typically produces similarities that are seen to be "skin deep" when examined in more detail. But this is not true. There are a multitude of highly specialized structures that appear abruptly in species not closely related. For example:
quote:
The Cypriniformes differ from most teleosts in having the majority of their species specialized as herbivores. The marginal teeth are lost, but the pharyngeal jaws form an effective grinding and crushing apparatus. They have a highly specialized mechanism that protrudes the jaws, as do the spiny teleosts, but it evolved separately in the two groups (Alexander). (Carroll, p. 120)
Certainly not skin deep.
On the contrary, the form of homoplasy known as convergent evolution is, in fact, "skin deep". Functional morphological features that are superficially similar, as for example the eye of vertebrates and cephalopods (both have a lens and retina), quite clearly arose through completely different developmental pathways. IOW, they evolved independently. On page 111 of Futuyma's "Evolutionary Biology", there is an excellent diagram and explanation showing clearly that the
differences in even such superficially nearly identical features as these two types of eye far outweigh their similarities - even tho' they serve a similar purpose for the organism. A few examples: retinal axons arise from the cell bases in cephalopods, but the cell apices in vertebrates; vertebrate nerve fibers run across the surface of the retina and converge in the optic nerve, creating a "blind spot", those in cephalopods run directly "back" from the bases into the optic ganglia.
Even more striking convergent examples abound: one of my favorites is the similarity of form but completely different development of (totally unrelated) species in the Cactacae (cactus - US), Asclepiadaceae (milkweed - Africa), and Euphorbiaceae (splurge - Africa). The similarity of form is in response to extremely similar selection pressures in similar habitats. IOW, the plants are filling similar niches and subject to similar environmental stresses, so similar phenotypical adaptations - not the same adaptation, or even from the same kinds of mutations - are prevalent and expected under evolutionary theory.
Could you please explain how the passage you quoted supports your position? Specialized structures are an understood part of homoplasy. However, those specialized structures are not identical in cases of convergent (or for that matter parallel) evolution - they are simply structures that because of environmental constraints are similar in function. The canines of
Thylacinus and
Canus lupus appear visually to be nearly identical, but they develop differently and are/were used in a completely different fashion.
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