Joined: Oct. 2005
| if the requirements of their niche cause adaptation toward the same morphological/functional solution. |
Cornelius Hunter responded
| A niche does not cause an adaptation. Adaptations occur via unguided biological variation, such as by mutations. They can then be selected for and become one step in a series of evolutionary changes. Because the biological variation is unguided, there is no target. And since the design space is large and a large number of designs and species are possible, the variation is not likely to repeat. |
Let's unpack the mistakes again. (Edited to add: I see that Mike addressed some of the same points while I was off-line. Thanks, Mike.)
A) Adaptations do not solely occur via unguided variations. They appear to occur mostly through mutations and recombination alternating with selection (among other pathways). Recombination can be guided, in the sense of sexual selection, and ecological selection can also easily be directional.
B) "Because the biological variation is unguided, there is no target." There is no target per se, but directional change is easily accomplished. With possible rare exceptions, mutations appear to be unguided, but selection is entirely capable of imposing directionality on the process. If there is differential reproductive success that is attributable in significant part to inheritable variation, and that preferential success continues over multiple generations, there will be a directional change in the population.
C) To the extent that the requirements of the niche are providing the challenge to reproductive success, it is fine to say that the requirements of the niche contributed to causing any resulting adaptations. Those requirements contributed to the existence of the problem, they helped provide the motivation and the directionality of the change, and thus they helped produced the end result.
D) "And since the design space is large and a large number of designs and species are possible, the variation is not likely to repeat." The key here is that the design space is indeed large, so exactly identical variations are indeed unlikely to repeat, but there are many broad categories of problems faced by organisms that come up again and again, so the broad categories of responses are again fairly similar. If you live in the water and need to either get food or avoid becoming food, you may well need to swim fast. As Wesley said, the laws of hydraulics are quite constraining, so streamlining provides a common solution, thus a lot of fast aquatic creatures end up looking similar. However, there is an infinity of ways to arrange minor details of form while being streamlined overall. Thus superficially similar streamlining should not be a surprise, while similar arrangements of minor details would be. Deadman provided an excellent example of this when he talked about overall similarities in skin folds in gliding mammals versus dissimilar details of construction in different groups.
There's no design reason that both a bat's wing and a bird's wing need to contain one scapula, one humerus, one radius and one ulna. There's no design reason that all bat wings need to be supported by five fingers, whereas all bird wings need to contain two fused fingers plus one more in the form of the alula. Why do all the bird versions contain so many similarities to each other that are never seen in bats, and vice versa? How come all birds have feathers but none have fur, while the reverse is true for bats? How come all birds share an alula and not a pteroid bone, whereas all pterosaurs share an pteroid but not an alula? Common ancestry within each of those groups provides an easy explanation. In a design world, any car can have windshield wipers, radios, and/or air conditioners. In an evolution world, only Buicks might have air conditioners, only Fords might have windshield wipers, and only Jeeps might have radios.
|This is why evolutionists are surprised by impressive similarities. |
But mostly we aren't. We are impressed by them, but our theory requires them.
|Cornelius Hunter: It is strange that evolutionists never get around to addressing the scientific issue [of convergence].|
|Me: The charge that evolutionists “don’t get around to this” is completely false, and can only be indicative of profound ignorance of the field, or mendacity.|
|Hunter: Most of the technical literature does not explore why comparative anatomy, for instance, is evidence for (or against) evolution, for the simple reason that it is not written from a theory-neutral perspective, but rather is written from an evolutionary perspective. Yes, the implications for evolutionary theory are explored, but typically only insofar as modifying the question of *how* evolution occurs, not *if* evolution occurs. |
Hunter's second response does not save the woeful wrongness of his initial claim that evolutionists don't get around to discussing convergence.
Furthermore, much of the discussion of convergence involves discussing the legitimacy of phylogenetic inferences ("does this particular similarity reflect a shared evolutionary history or not?", where "not" includes convergence). However, "not" also includes ID. If the answer was always that particular similarities could never confidently be attributed to a shared evolutionary history, then that would raise the issue of "if" evolution occurs, contrary to Hunter's claims.
|(Hunter) From a theory-neutral perspective, what is it about the bat and horse similarities that are "deeper" and a "result [of] common descent" ? |
Already answered. Deadman's answer is excellent, and I already said that if we see the same embryological tissues contribute to two features, the same genes activated during their construction, utilization of the same developmental pathways, and the same bones ending up in much the same places in the same basic relationships to adjacent bones, nerves, blood vessels, and so forth, then we can make a reasonably secure claim of homology. If we additionally have a fossil record that shows similar structures or a gradation of change in probable intermediates then the claim is that much stronger.