>the lack of transitional forms in the fossil record...I mean that
>why don't we find the situation to be one wherein the literally
>thousands of samples mutants or transitional forms to every one
>sample of the stable forms -- by absolute quantity, not type. That
>would seem to be the logical consequence of Darwinian evolution.
>Also consider the world as it exists today. Forget about fossils.
>Why are there not 1000 different forms of tiger mutants for every
>"normal" tiger? Did evolution suddenly stop happening with tigers?
>Same for all other animals.<
Consider the range of variation seen in humans or dogs or any other
species that you are familiar with. Likewise, there are several
varieties of tigers (plus some recently extinct ones, like the black
Javanese race). Variation is ongoing. However, looking at
individual slices of time, the variation is not as obvious, whether
in the fossil record or at present. For example, much of my research
has focused on Cenozoic shallow marine faunas in the southeastern
U.S. The fossil deposits are rich, but they only represent time
intervals when the sea level was higher than present and which have
not been removed by subsequent erosion. Even if a lineage
experienced constant gradual change over the represented time
interval, what we would see would be a series of samples with limited
variation within the sample and distinct differences with older or
younger samples, becausethe transitions occurred in missing
intervals. In fact, there are several examples of forms that are
interm!
ediate between others, and some species in some layers that show high
variability. However, the sampling and preservation bias alone would
produce the appearance of a more stepwise process rather than a
smooth process due to sampling and preservational bias. Another
problem arises from the effort to identify and name specimens. If
you are not sure what to call something, it tends to get put aside.
In particular, biostratigraphic studies (trying to identify the layer
based on the types of fossils) look for distinct, identifiable
specimens, not intermediate forms.
Also remember that "if it ain't broke, don't fix it". If something
works well, natural selection will act to keep it from changing
rather than to change it. Solemyoid and nuculoid bivalves from the
mid-Paleozoic look very similar to modern ones. Having found stable
niches, they stayed there.
>Now there was an alternate theory advanced by Gould. I know just a
>little about it but it seemed a better match to the data than does
>Darwin's - or Dawkin's - notions from my layman perspective. I also
>know that NOVA suppressed one of their own shows with Gould's views.
>My perception is that despite a better match to a great deal of the
>most recent evolutionary data, "evolutionists" reject it because it
>gives an opening for "creationists" to say "aha".<
Certainly in the paleontological community there is general
acceptance of the widespread occurrence of punctuated patterns.
There remains disagreement as to the relative frequency of punctuated
versus gradualistic patterns in evolution. The one study I did
specifically addressing the issue looked at two kinds of clams. One
turned out to show a punctuated pattern and the other showed gradual
change. There is speculation that gradual change may reflect low
levels of selective pressure. When the going is easy, many sorts of
mutants will still be able to survive and reproduce, and perhaps
gradual change will occur. If the pressure is higher, deviations
from the mean are more likely to be either significantly detrimental
or significantly better, so that there are periods of change
punctuated by rapid shifts.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487 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
Droigate Spa
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