janc@uofm-cv.UUCP (Jan Wolter) (03/03/84)
[Playing with the idea of limited variation] An comment in a recent note on creationism caught my attention. The idea seems worthy of consideration despite the source. I would be interested in other ideas on this subject. Quoth A. Ray Miller: Creationists claim that there are limits in variability to viable organisms. All are agreed, at least, that some variation does occur. After all, there are dachshunds. I believe the claim is, that while it is possible to evolve wolves into dachshunds, it is not possible to evolve apes into men. Clearly our meaning here is not simpily that it is impossible for a human to be born from ape parents. Both Creationists and Evolutions agree that only small variations can be made in a single generation. The concept of limited variation means that the is a limit to how much the small changes can accumulate. The immediate question is *how much* those changes can accumulate. This has to be defined in terms of the base form, which, I suppose, would be the form as originally created by God. We can perhaps imagine that as part of the creation of each species, God defined the limits on its variation. A more interesting question is how those limits are enforced. Ideally, there would be a biological mechanism that limits change. Demonstrating such a mechanism would be, I think, another excellent way to falsify the evolutionary theory. Since the limits must be enforced in terms of distance from the base forms, some measure of biological distance from the base form must be stored in all organisms. Evolution is composed of separate processes of random variation and natural selection. To limit evolution we need either to have a mechanism which causes less environmental pressure to be exerted on derived forms, or less variation to occur in derived forms. The latter seems the more fertile path. Let us attempt to describe the effects of such a mechanism. We postulate random variation is smaller in derived forms than in base forms. For discussions sake, lets assume that wolves are a base form. When a wolf parent gives birth to cub which is slightly different than it's parent, the potential for variation amoung the cub's children will the slightly less than it's parent. We would, thus, expect to see a little less variation amoung german shepard pups that wolf cubs, and much less amoung dachshund pups. Since the potential for variation decreases geometrically as we get further from the base, we have an absolute limit on variation. But, suppose we form a project to breed wolves from dachshunds. Will the resulting dachswolf have less variation than the very similar base wolf? I suspect that if this were the case continued variations in the wolf species would have exhausted their variablity long ago. Perhaps we can conceive of a dachshunds genes as wolf genes "bent out of shape." Thus the random variation in a dachshund would tend more strongly toward regaining wolf traits than toward new traits. As we get further from the base form, our random variation would no longer be random, but would be entirely toward regaining lost traits of the base form. This almost sounds feasible. Basically we are saying that once a species has changed too much all we get is throwbacks to the original form, so if evolution continues, it will be back towards the original form. With this plan, God supplies species with a range of possible variation, so they can adapt to environmental changes, without departing too far from the Grand Design (and without offending the sensibilities of dips who don't want to be related to apes). Let me clarify what would have to be shown to prove this idea. It would have to be shown that the incidence of throwback traits relative to new traits increases with increased distance from the base form. In conventional evolutionary theory, throwback traits will gradually be purged from the gene pool, so they will be rarer in older forms, and thus in forms which are further from the base form. If the converse could be shown, it would be good evidence for the model proposed above, though to put it on a firm foundation, a mechanism would have to be found. Of course, even proving this hypothesis would not prove that the species had been created. It would however force us to look elsewhere for a speciazation process. Jan Wolter University of Michigan
mmt@dciem.UUCP (Martin Taylor) (03/07/84)
=================
A more interesting question is how those limits are enforced. Ideally,
there would be a biological mechanism that limits change. Demonstrating
such a mechanism would be, I think, another excellent way to falsify the
evolutionary theory.
=================
(Limits, in the above == limits on variability of species form).
I don't see the connection. Surely there exists a perfectly natural
set of limitations on the variability of any species. Some limits
apply because the organism would die (and many do, before and after birth),
some apply because the organism in its modified form would find no
ecological niche and would be unlikely to reproduce as effectively as
the "mainstream" version of the species.
Isn't the filling of ecological niches what lies behind punctate
equilibrium? We know from the results of breeding domestic animals
that drastic changes can be developed in a few tens of years when
selection is deliberate. The genetic mechanisms ALLOW very fast changes
in species form. But in nature, the empty niches created by the
Lords of Breeding (us) seldom are there for the changed forms to
occupy. If some disaster occurs and niches open up, then rapidly varying
forms can occupy them. If there is a general extinction from whatever
cause (sea-level transgression, asteroidal impact, nuclear war), then
the whole niche structure ceases to be self-supporting and the whole
list of major and minor species can be rapidly transformed.
In sum, evolutionary theory seems to demand a biological mechanism
for limiting species variability, rather than being open to falsification
if one were discovered.
--
Martin Taylor
{allegra,linus,ihnp4,uw-beaver,floyd,ubc-vision}!utzoo!dciem!mmt