dimitrov@csd2.UUCP (Isaac Dimitrovsky) (04/30/85)
[] For the benefit of net readers who don't have a pushdown automaton handy, I won't nest my quotes more than two deep. The topic at hand was the flying squirrel, intermediate status of. >> The point of the flying squirrel example is NOT that the squirrel can >> really fly. ... The point [is that] ... at least in the case of wings, >> it is possible to have intermediate forms which are useful for >> gliding and short flights but are not capable of full flight. > I will not dispute that they can glide and that they are not capable of > full flight. That is obvious. I am of course unconvinced that they > are intermediates (that is, intermediates which developed from a > non-intermediate). The skin flaps are not wings and there is no > evidence that they ever will be. There is also (as far as I am aware) > no evidence that they ever were anything but skin flaps. > . . . if you wish to use this as evidence of an > "intermediate" to press your case, I will object and demand evidence > which, I think, you shall be unable to produce. I was puzzled at first about why you seemed to understand my note as arguing that the flying squirrel was positive evidence for evolution. Then I saw the words "intermediate forms" in my note (On a system with icons, I guess those should have been accompanied by a red flag :-) ). I will try to explain fully what I meant by intermediate below, but roughly speaking I meant a physical intermediate, not an evolutionary one. I would be glad to discuss with you whether intermediates can be considered as positive evidence for evolution. This certainly doesn't seem like an obvious question to me. In any event, I think there is much more convincing (at least to me) evidence from other sources. (Yes, I would also be glad to discuss the other evidence on both sides, just as soon as we get this topic over with). However, as should become clear on rereading the original notes, I was not advancing the flying squirrel as positive evidence *for* evolution, but was using it to refute an *objection* to evolution that had been made. The objection, as it appeared in the note that started all this: > THE SCIENTIFIC CASE FOR CREATION: 116 CATEGORIES OF EVIDENCE > > I. (Life Sciences): THE THEORY OF ORGANIC EVOLUTION IS INVALID. > > A. EVOLUTION HAS NEVER BEEN OBSERVED. > > 10. All species appear perfectly developed, not half developed. They > show design [a]. There are no examples of half-developed feathers, > eyes [b], skin, tubes (arteries, veins, intestines, etc.), or any of > thousands of other vital organs. For example, if a limb were to evolve > into a wing, it would become a bad limb long before it became a good wing. To paraphrase this objection: We find many structures in nature which are so complex and well developed that it is inconceivable that they evolved in a single step. And so by the theory of evolution, we should expect to find intermediate forms in the development of these structures in nature or in the fossil record. But we do not find these intermediates. And in fact, for some structures, such as wings, it is impossible to imagine an intermediate form in the development of the structure which would be of any advantage to the creature possessing it. To refute this objection for a particular structure, we can find a set of physical intermediates for this structure in nature and the fossil record. And these intermediates should be close enough to each other that it is reasonable for each one to have evolved into the next relatively rapidly. Failing this, we can at least try to hypothesize intermediate forms of the structure which would be beneficial even though they are not full versions of the structure. The flying squirrel was advanced to refute this objection for the case structure = wing, using the first tactic. So what I meant by intermediate, and what is needed to refute the objection, is a physical intermediate, or set of intermediates, which could reasonably have evolved into each other. For the wing, some of these intermediates could be 1) folds of skin along the sides of some tree climbing animals (presumed to provide camouflage). 2) flying squirrel (and other physically intermediate wings). 3) full wing. And once again, the evidence *for* evolution is a separate question; the point of this argument is to refute the *objection* to evolution above and specifically to explain how the evolution of the wing was *possible*. The evidence that evolution in general and evolution of the wing in particular occured is another topic. Isaac Dimitrovsky