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Several questions on evolution, and mutation (rate)

Radford Neal radford at cs.toronto.edu
Tue Sep 3 22:21:06 EST 1996


In article <dyanega-0309961906530001 at catalpa.inhs.uiuc.edu>,
Doug Yanega <dyanega at denr1.igis.uiuc.edu> wrote:

>> 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. 

Ahh, come on.  Are you seriously maintaining that this sort of
simplistic accounting is a practical way of describing how the genomes
of different species differ from one another, or change with time?
What's the frequency of the allele if it is present in the genome, but
never transcribed?  How do you count transposable elements?

>> 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.

Actually, we generally *don't* have definitions, *especially* for key
concepts.  What's the definition of "species"?  I know there's a hoary
old one about lack of inter-breeding, but it's clearly inadequate.
Try asking a physicist for definitions of "mass" or "energy" - you'll
either get nothing at all, or a meaningless phrase, or their latest
(probably false) theory about Higgs bosons.  For "entropy", you'll get
two completely different definitions (a thermodynamic definition and a
statistical physics definition), which it is thought are equivalent,
that being a substantive conclusion of physics.  Neither of these
allow for the surface area of a black hole making a contribution to
entropy, but that didn't stop physicists from deciding that it did.
The real meaning of the concepts is always deeper than the textbook
definitions, and in particular, any definition that fails to capture
the reason the theory is considered important is clearly a provisional
technical sort of thing, contingent on current beliefs.


>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?

It is certainly conventional usage to say that evolution occurs when
there are changes in allele frequencies, even if these changes are not
accompanied by speciation, but this is because biologists believe that
the same process *does* lead to speciation in other cases.  If it were
discovered that changes in allele frequencies *cannot* lead to
speciation, it is doubtful that such changes in frequencies would be
referred to as "evolution", because this word has been extensively
applied to the process (whatever it is) by which the diversity of
species on Earth has come into being.  That's what the word really
means.

   Radford Neal



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