From: bivalve (bivalve@mail.davidson.alumlink.com)
Date: Tue Oct 21 2003 - 18:24:44 EDT
Don wrote:
>> Proposed mechanisms of evolution are a different story. Support for these comes from plausibility arguments, and such arguments aren't falsifiable. You either believe them or you don't. Nevertheless, they are widely accepted because they are the best natural mechanisms we know of.<<
Walt replied:
>That is the basic issue raised by Johnson ===>
>namely, that he doesn't think that "natural
>mechanisms" are at work. One does not address his
>concerns or arguments by saying that this is "the
>best natural mechanisms we know of". It can only
>be addressed by making predictions and
>demonstrating that they work and that those alone
>are sufficient to demonstrate that evolution of
>species can happen.
The issue of natural mechanisms also ties into the god of the gaps problem. I think many proposed methods of evolution are pretty credible explanations of ways in which species evolve. I am not a priori commited to natural explanations; however, I think theological and observation evidence indicate that God uses natural methods the vast majority of the time, so I think that natural explanations are likely to be correct.
New species are made all the time. Several different mechanisms can be observed at work, though it is often tricky to tell when to draw the line and say that a new species exists. For one thing, the definition of a species is debated.
The clear-cut cases are hybrids. Through various methods (often asexual), some hybrids can reproduce. This is extremely common in plants and widespread in animals (not birds or mammals, though). Usually the hybrid cannot reproduce with either parent species, so it is a distinct species by the definition of reproductive isolation. Often the hybrid is also morphologically distinct. If the hybrid can reproduce with other hybrids, however, a new species is clearly present. If it can reproduce asexually, defining species becomes more problematic, but this is also generally consideed to be a new species. This situation would be an example of genetic isolation producing new species. Another is Glenn's model for the origin of Homo. He suggests that the chromosomal rearrangement that distinguishes us from chimps produced a barrier between Adam and Eve versus prior hominids. Such rearrangements do make reproductive barriers in many cases.
There is also the development of premating barriers to reproduction. A recent study looked at shell coiling in snails. Most snails open to the right if you hold the apex up. However, some open to the left. In some taxa, a left-handed individual cannot mate with a right-handed individual. Thus, the single mutation that switches coiling direction can create an isolated population.
Another sort of barrier that can divide a population into two species comes from physical separation and corresponding specialization along different lines. A well-studied example comes from fruit flies. One North American species courts on, mates on, lays eggs on, and develops in hawthorn berries. When people brought apples over from Europe, some of the flies took up living on apples instead. However, apples have several differences (ripening time, time from ripening to rotting), etc. The flies have begun to specialize for one or the other, and at least one genetic difference is now known.
Physical distance plus genetic drift may also be a factor. There are several pairs of bird species in the western versus eastern U.S. with relatively small differences. However, the males have distinct songs, so females head for the right males. There is rarely any obvious selective merit in the differences; rather, it seems likely that the two populations became isolated by distance and then gradually drifted apart as mutations accumulated in one or the other.
Determining exactly what factors played the largest role in the evolution of a particular species in the past is very difficult, although lines of evidence supporting a particular model may be found. However, we can observe such factors at work in the present.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487-0345 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa
---------- Original Message ----------------------------------
From: Walter Hicks <wallyshoes@mindspring.com>
Date: Tue, 14 Oct 2003 08:34:51 -0400
>
>
>Don Winterstein wrote:
>
>> The fact of evolution is easy to falsify in principle: Just find a bunch of fossils
>> grossly out of sequence in undisturbed formations. For example, find homo
>> sapiens skeletons in undisturbed Carboniferous limestone. Evolution emphatically
>> predicts such things do not exist, so to falsify it, just find them. YECs in fact
>> have claimed to have made finds of this sort (e.g., human footprints alongside
>> dinosaur tracks), but none have stood up under scrutiny.
>>
>Actually, the "fact" of evolution was not my
>question. That is a lot of the difficulty of
>working with evolution. The same term is used for
>the theory and fact (or data). But you raise a
>good point. The flood catastrophe folks have to go
>through a lot of convoluted reasoning to get
>around the sequence.
>
>
>>
>> Proposed mechanisms of evolution are a different story. Support for these comes
>> from plausibility arguments, and such arguments aren't falsifiable. You either
>> believe them or you don't. Nevertheless, they are widely accepted because they
>> are the best natural mechanisms we know of.
>>
>
>That is the basic issue raised by Johnson ===>
>namely, that he doesn't think that "natural
>mechanisms" are at work. One does not address his
>concerns or arguments by saying that this is "the
>best natural mechanisms we know of". It can only
>be addressed by making predictions and
>demonstrating that they work and that those alone
>are sufficient to demonstrate that evolution of
>species can happen.
>
>I believe from all of the avoidance I see, that
>one cannot do the above and, therefore, there is
>no valid theory for the evolution of species. When
>(or if) there ever is, people will stop dancing
>around the question IMO.
>
>For the record, I happen to lean heavily towards
>evolution of man as true. However, that it is an
>opinion, and I recognize it as such.
>
>
>Walt
>
>
>
>
>
>
>>
>>
>> I suppose mechanisms of all historical sciences lean heavily on plausibility
>> arguments. However, geology has lots of obvious modern analogs, while those for
>> evolution are less obvious.
>>
>
>Thanks for your comments, Don.
>
>
>Walt
>
>
>===================================
>Walt Hicks <wallyshoes@mindspring.com>
>
>In any consistent theory, there must
>exist true but not provable statements.
>(Godel's Theorem)
>
>You can only find the truth with logic
>If you have already found the truth
>without it. (G.K. Chesterton)
>===================================
>
>
>
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