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Several questions on evolution, and mutation (rate)

Doug Yanega dyanega at denr1.igis.uiuc.edu
Tue Sep 3 19:05:35 EST 1996


In article <96Sep3.191953edt.1015 at neuron.ai.toronto.edu>,
radford at cs.toronto.edu (Radford Neal) wrote:

> 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?

Simple. The frequency is ZERO, as is the frequency of ALL blood type
alleles in that species. If it doesn't have that particular gene, it can't
have the allele. But it has its own genes with their own alleles. Anything
that has genes has alleles; even if the frequency of an allele is 100%,
it's still considered an allele. The concept is independent of chromosome
number, size, or whatever. An allele is simply any form of a gene.

> 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.

Nothing can evolve unless it possesses genes, which means it also has
alleles. "Genetic composition" and "frequencies of alleles" are
essentially synonymous, though this does exclude non-coding genetic
material. I'd be happy to agree with a molecular biological definition of
evolution (any change in the frequencies of genetic sequences in a
population), if that would please everyone concerned.

> >... 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. 

Then we are at an impasse, because I think this statement is gibberish,
and that a rigorous definition is essential to any scientific theory, not
"occasionally useful". There is nothing else besides a *definition* that
can establish what a theory is or is not. That's why we *have*
definitions.

>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.

Depends on how you define "Lamarckian Evolution," doesn't it? You must do
so, in fact, in order to distinguish it, unless of course you believe that
it proceeds by alteration of an individual's germ line genome - in which
case it would still be evolution, but you will have hypothesized a
non-traditional mode of "directed mutation". That is a separate issue from
evolution _per se_.

> 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.)  

You have, and I do below.

>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.

What Mr. Beorn said, was, verbatim:

> I.e. no evolution occurred - 
> adaptation, variability of a species yes - but not evolution.  No new 
> "creature" was created.  

He *specifically* confused speciation with evolution, and admitted himself
that he believed species could be variable and adapt. In effect, he
admitted that evolution occurred, but denied that evolution leads to
speciation; but what he SAID was this was not evolution. I am perfectly
within my rights to point out to him that he has confused the issue. Do
you or do you not agree that speciation and evolution are NOT synonymous?
Why on earth would we have two terms in the first place if they both meant
the exact same thing? I'm just trying to keep the air clear, while you
seem fond of obfuscation. 
   I have never denied anyone their right to question whether evolution
leads to speciation. I'm certain that it can, as I am fully aware there is
evidence that it can - but I also realize it does not *have* to. I just
think it's wrong for people to coninually confuse the two things.

Doug Yanega     (dyanega at mail.inhs.uiuc.edu)
Illinois Natural History Survey, 607 E. Peabody Dr. 
Champaign, IL 61820  USA  (217) 244-6817 fax:(217) 333-4949
affiliate, University of Illinois Dept. of Entomology
  http://www.inhs.uiuc.edu:80/~dyanega/my_home.html
"There are some enterprises in which a careful disorderliness is
    the true method" - Herman Melville, Moby Dick



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