Re: Is evolution really the central theory for all of biology?

From: David C Campbell <>
Date: Tue Sep 20 2005 - 18:38:43 EDT

>This means that evolution can explain a wide range of
>outcomes. This means that any one particular outcome does not >confer
much increased confidence in the validity of the hypothesis.

True. However, this means that evolution is difficult to disprove and
certainly is not a valid argument against evolution.

>"It's not special pleading if there are real examples of convergence, >
i.e. it's part of what we expect in the complex biological world and
>there are ways to distinguish between them."
>Real examples of convergence are precisely why evidential claims,
>such as the vitamin C pseudogene, constitute special pleading. The
>only examples of "real" convergence we know are these mutational
>hotspots where identical mutations are observed to occur
>independently. Hence claiming that the vitamin C pseudogene
>mutations are evidence for common descent *is* special

Two problems:
First, this sort of arguing, if it were valid, would equally disprove
ID, since purported gaps are evidence of ID action and things that work
without gaps are evidence of ID as advance design. Also, the decision
as to whether something reflects convergence versus homology is a
decision about the relative complexity of different possible patterns.
If similarity in complex biological structures can all be dismissed as
convergent, they do not provide a valid example of low probability that
might require ID-type design.

Secondly, this is claiming that because some examples of convergence
are known, therefore nothing can be confidently identified as due to
common descent rather than convergence. Convergence can be observed in
the lab in rapidly evolving bacteria and viruses, or in in vitro
evolution, in addition to the above examples. However, the very same
experiments demonstrate vast amounts of homologous similarity.

Here's an example of sorting out convergence versus homology in a
fairly uncontroversial (in the sense that people don't care about
evolutionary claims relating to it as much as they do about primates)
The genus Fusconaia uses all four gills to brood its young. Based on
this feature, it has been classified as closely related to Quadrula and
Amblema. However, apart from that it is fairly similar to the genus
Pleurobema, which only broods in the outer gills. (These are all
freshwater mussels from North America, within a single family.)
Antibody-based analysis of similarity and DNA sequences for one nuclear
and three mitochondrial genes all indicate that true Fusconaia is
closely related to true Pleurobema, but some species closer to Quadrula
or to Amblema have wrongly been assigned to Fusconaia. Furthermore,
other mussels also have significant anatomical and molecular
differences and appear to have independently made a switch in gill
brooding pattern. Thus, there is good evidence for some convergence in
the use of gills for brooding in this group. The good agreement
between other morphological features and all four genes analyzed
supports the conclusion that those are indicatingthe true evolutionary

>The massive and detailed convergence in biology was a surprise for,
>not a prediction of, evolution.

No. Several examples of convergence were known prior to Darwin (e.g.,
whales being mammals, not fish), so they arenot all surprises for
evolution. Evolution predicts that features that enhace survival will
be favored. Features that work in one organism have a good chance of
working in another organism (unless they result in unsuccessful direct
competition) and are at least within the realm of possibility (which
might not be the case for features that never appear in any organism,
e.g. wheel and axle above the molecular level). Thus, convergence is
strongly expected to occur. Precise prediction of exactly what
convergence will occur requires much more detailed information than the
basics of natural selection, but some sorts of convergence can be
predicted fairly well (e.g., anything that takes up fast swimming must
be streamlined).

>Nor do there exist unambiguous ways to distinguish homologies from
>analogies. Ultimately it is both subjective and circular.
>Subjective because the evolutionist must draw from a variety of
>criteria to decide how make his judgement. Circular because he must
>assume evolution occurred. Without first assuming evolution, then
>the evolutionist would have to reckon with all the negative evidence
>which is being ignored.

Drawing from a variety of crieteria does not make it subjective. If
the different criteria give different direction, then one might
subjectively or objectively choose among them. (Of course, the
selection of objective criteria might itself be subjective or
objective, etc., but at some level every decision eventually rests on
subjective criteria.)

For example, I can run a parsimony analysis of DNA data. I am using
objective criteria to assign the DNA similarities to homology or
convergence. Those objective criteria are not guaranteed to actually
correctly identify homology versus convergence 100% of the time, and
applying the same criteria to a slighty different data set may give
results that slightly conflict with the first assessment of homology
versus convergence. However, some examples are very strongly supported
as convergent and some are very strongly supported as homologous. If
problems of poor support and inappropriate analysis are taken into
account, I have not seen major differences in evolutionary patterns
supported by different large data sets during my decade or so of
working with evolutionary analyses of mollusks.

>To make the case for evolution we need two things. First, we need >good
strong evidences and arguments that do not fall apart under
>inspection. And second, we need good defenses against the
>problems that exist. Right now we have neither one of these.

I have yet to encounter any purported evidence against evolution that
does not fall apart under inspection. However, the molecular data,
morphological data, fossil record, and other evidence consistently fit
the patterns expected evolutionarily. Normal science is done not
merely because a paradigm has been accepted but becasue it works.
Those who propose new ideas must not only identify the existing idea as
an established paradigm; they must demonstrate that the new idea better
explains the data than the old one.

If there were significant disparity between molecular and morphological
patterns, or if the fossil record did not show a series of transitions
and a sequence from less complex to more complex, these would be
reasonable evidences against evolution. There is noise in the data, as
for any measurement. The match between different lines of evidence is
not perfect. However, the patterns are so strong in many cases as to
leave no scientific reason for doubt that the match is good.

Dr. David Campbell
425 Scientific Collections
University of Alabama, Box 870345
Tuscaloosa AL 35487
"James gave the huffle of a snail in
danger But no one heard him at all" A.
A. Milne
Received on Tue Sep 20 18:41:04 2005

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