Several questions on evolution, and mutation (rate)

Doug Yanega dyanega at denr1.igis.uiuc.edu
Fri Sep 6 12:44:24 EST 1996


In article <50lcme$1vr at hecate.umd.edu>, me at ram.org wrote:

> How do you differentiate between mutations that give rise to a new
> function, and mutations that do not?  

Either is considered evolution (a change from zero to non-zero allele
frequency), so they are equivalent; no need to differentiate. A great deal
of evolution can be neutral.

>The evolution of function is an interesting
> topic in and of itself, which not many people think about (though I do
> know of published attempts to attempt to create function, it has not
> been successful).  This is what I've commonly heard (among
> biologists/biophysicists) referred to as evolution.

Maybe over coffee in the morning, but not in the literature, you don't.
Then it's called the evolution of function (as you yourself call it!), not
just "evolution."

> How's that mutation different from a mutation that simply changes a
> base pair, or an amino acid, without changing the function of the
> protein?

If it creates a new allele, then it is no different.

> What I'm saying is that to observe new function evolve, you would have
> to make sure that the gene or genes that code for the function did NOT
> exist in the population before.   Otherwise, how would you separate
> out natural selection and what I call evolution?

This, I think, is a fallacy for any case where a "function" is a property
of several genes acting in concert - for most macroscopic organisms, there
are going to be a whole LOT of such cases where gene interactions like
pleiotropy are very important. The terminology "to observe new function
evolve" is a sloppy use of the word "evolve". What you APPEAR to mean is
"to observe the origin of a new function" whereas the more literal
interpretation is that you're talking about the *spread* of the new
function throughout the population. Both events - the origin of a new
trait (frequency from zero to non-zero) and its spread (low to high
frequency) are parts of the evolutionary process, but the phenomena
controlling them are different. 

As you say in a subsequent posting:

>Say you have two related
> antibiotics.  Currently, in a population of bacteria you see
> resistance to one antibiotic, but not to the other.  In a few years,
> you begin to see resistance to another antibiotic in that same
> population.  Now, there are two explanations (in this context) for
> what happened: one, the gene for resistance to the second antibiotic
> was ALREADY PRESENT (as a variant of the first gene, either in the
> population or on the genome) in the bacterial population, and was
> NATURALLY SELECTED for.  Two, the gene for resistance EVOLVED from the
> first gene, in some manner, and was THEN natural selected for.  These
> are two different processes.

No, no, no. In BOTH cases resistance has evolved. In one case it evolved
from zero to non-zero frequency VIA MUTATION, in the other it evolved from
a very low frequency to very high VIA NATURAL SELECTION. From this and
your other postings, and as Jim Foster pointed out, you seem to be trying
to make the term "evolution" *synonymous* with "mutation", when mutation
is simply one of the modes by which evolution occurs, as is natural
selection, as well as genetic drift - definitely a change of pace from all
the folks who try to synonymize it with "speciation" or those who try to
synonymize it with "natural selection", but ALL such attempts are [brace
yourself for a big word] synecdoches; that is, you are like the blind men
and the elephant, each trying to define the whole concept by focusing on
only ONE of its components or corollaries.
   My big metaphor for the day. I believe I'll retire from this thread, on
that note - I gotta pack for my move to Brazil.

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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