From: bivalve (bivalve@mail.davidson.alumlink.com)
Date: Thu Oct 16 2003 - 15:52:54 EDT
Here are some of the sorts of things that come to mind for me regarding the testability of various evolution-related issues.
At a very basic level, all evolution requires to work are the three points that Darwin noted. There must be variation within a reproducing population. These variations must be heritable. These variations must differ in rate of survival.
These three conditions are quite easily met and observed to work in experimental situations, studies of natural populations, or in computer simulations.
All three points are subject to various influences. The relative roles of these factors vary greatly. Thus, there are several factors that can influence mutation rate or expression of mutations. The patterns of inheritance are largely uniform, but especially in bacteria things can jump around. Finally, all sorts of things affect survival, including environmental factors, competition and other biological interactions, and catastrophic events.
For a given situation, it may be possible to get an idea of the relative influence of particular factors. For example, with regard to the range of variation in the Cambrian, a structural explanation may be better than Gould’s idea of a random set of events. R. D. K. Thomas and others modeled the theoretical range of shapes available to animals. Most of the options were already taken by the end of the Cambrian, so there is not much room for anything novel in the subsequent intervals. While this does not tell whether intelligent organisms would evolve if one could replicate a start from the early Cambrian (nor whether they might be chordates or mollusks), it does suggest that the general shapes of animals would be about the same. Conversely, in early land plants the constraint of maximum strength in branch configuration applies only to the older forms. By about the late Devonian, plants were able to make branches strong enough so that weaker branch configurations were ac!
ceptable. Likewise, for punctuated versus gradual evolutionary patterns, some organisms in some time intervals show one or the other. The relative total impact of any one factor on all of evolution is debated, and probably unknowable.
The extent to which evolution has played a role, e.g., a universal common ancestor of all living organisms or the development of life from primordial soup, is more of an historical question. However, it is still subject to testing through retrodictions. For example, evolution predicts that simpler fossils should occur before more complex ones. Through the early Precambrian, we just find fossil bacteria. In the mid-Precambrian, protists and algae appear. In the very latest Precambrian, large animals are present, but they seem to lack many of the more complex structures of later animals. The bacteria are still present, too; it’s not a march towards greater complexity but rather an increase in variation, which includes greater complexity. Complexity has its advantages, so there is some selective pressure in that direction, but there are downsides as well. E.g., a sponge will do better than a human when squashed through a sieve because of its lesser complexity; however, !
the human is better able to anticipate and try to avoid getting squashed through the sieve.
Evolution also predicts that organisms should occur in a consistent sequence through time, because they evolve at a particular point in time and may also die out or evolve into something else. (Contrary to some young-earth propaganda, slightly extending the range of a particular kind does not violate this.) Even though some of the contacts in the Grand Canyon are not obvious from a look at the rocks, examination of the fossils makes it obvious because there is an abrupt change in the fauna. Even within a flood geology framework, it would make more sense to invoke an unconformity (of brief duration) to explain this change. (The Muav-Redwall contact is a particularly bad choice to try to deny that it is an unconformity, because in some places the Temple Butte is in between them, and the Temple Butte-Muav contact is obviously unconformable).
Evolution predicts that we should see many intermediate forms in the fossil record, which we see.
Evolution predicts patterns of similarity that agree well with the physical and biochemical pattern observed in organisms.
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
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