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Several questions on evolution, and mutation (rate)

Radford Neal radford at cs.toronto.edu
Tue Sep 3 18:20:10 EST 1996


In article <dyanega-0309961425120001 at catalpa.inhs.uiuc.edu>,
Doug Yanega <dyanega at denr1.igis.uiuc.edu> wrote:

>> Even the most casual acquaintance with the variety of organisms on
>> Earth should reveal to you that they differ in more than the
>> frequencies of alleles.  The concept of an "allele" applies only when
>> the set of genes is regarded as fixed, which is clearly not the case
>> when considering organisms that differ wildly in the number, length,
>> and organisation of their chromosomes. 
>
>This has nothing to do with the concept of an allele.

Really?  Perhaps you would like to elucidate.  Could you tell me the
frequency of the allele for type "A" blood amongst redwood trees?

If you can't do this, then you really have to admit that "change in
the frequencies of alleles" is not an adequate definition of evolution.

>... Selection is not required for evolution to occur, though it is one
>type of evolutionary process. Evolution can occur without leading to
>speciation, but speciation cannot occur without evolution (there is no way
>for something to be a new species without possessing alleles different
>from its ancestor's). Now perhaps you can understand why it is absolutely
>*essential* that there be a rigorous standard definition; it helps one
>avoid confusion about the different levels of process.

You are deeply confused about the nature of scientific theories.  The
sort of technical definition you insist on is an occasionally useful
internal device for a theory.  Such definitions do not establish the
meaning of the theory in a wider sense.  The meaning of the theory of
evolution is the explanation it gives for the development of life on
Earth.  The current belief is that this development is mediated by
changes in the genetic material in organisms (though "changes in
frequencies of alleles" is a far too simplistic account of this).  If
you assume that this belief is correct, then you might perhaps be
tempted to redefine evolution as changes in the genetic composition of
populations, and this might occasionally have technical advantages.
However, this definition is completely inappropriate if the belief on
which it is based is being questioned.  For example, if someone claims
that Lamarckian evolution is the *real* explanation for how life on
Earth has developed, it is fatuous to say that evolution is *defined*
as changes in frequencies of alleles, and therefore Lamarckian
evolution is a contradiction in terms.  Lamarkian evolution is very
likely wrong, but it is not wrong by definition.

As I recall, this discussion began when you presented evidence that
the frequencies of alleles can change, saying that this showed that
evolution occurred.  (Unfortunately, I don't have the old post, so
correct me if I've mis-remembered this.)  Someone said something like,
"but do these changes in allele frequencies ever result in a new
species being produced?"  You then proceded to ridicule their
ignorance of evolution, saying that evolution is now *defined* as
changes in frequencies of alleles.  It is your response that deserves
ridicule.  The question whether new species can be created in this
fashion is an important one, at the heart of whether evolution is in
fact the explanation for the diversity of life on Earth.  This
question can only be answered by evidence, not by definition.

    Radford Neal



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