Several questions on evolution, and mutation (rate)

James Foster foster at cs.uidaho.edu
Thu Sep 5 11:05:53 EST 1996


Ram Samudrala (ram at mbisgi.umd.edu) wrote:
: James Foster (foster at cs.uidaho.edu) wrote:

: >Well, "evolution" does mean "change".  But to biologists it really
: >means "a change in the distribution of characters ocross
: >generations".

: Well, I'm a biologist in a sense, and I just disagree with that
: definition of evolution.  In fact, this is the first time I've come
: across it, even though I've discussed this topic with various
: biologists.   

I got it most explicitly from Grant, the guy who studied selection and
evolution of Darwin's finches.  Perhaps there isn't one single sense in
which these terms are used, but some distinctions will help make it
easier to discourse.  

By the way, I'm only a biologist "in a sense".  I'm a computer scientist
by training, but I've been doing computational biology work for a few
years.

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

Why should you?  mutations which lead to changes that increase in
frequency due to selective pressure are "beneficial", while those that
don't aren't.  Of course, this classification can change overnight with
the advent of a drought or an invasion of predators.

And what's a "new" function, anyway?  Usually mutations only
incrementally change some already-present characteristic, like
sensativity to light, resistance to antibiotics, or length of beak.

: It could pass it on.  What I'm saying is that at some point, for new
: function to evolve, it must have happened in one organism (it could
: happen simultaneously also), and subsenquently been selected to spread
: to various generations.  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.

Wouldn't resistance to an antibiotic, or ability to produce viable
offspring, be new functions?  These rarely spring into being de novo.
They begin in a small degree, and then increase in degree.  This is one
of the (many) falacies in the anti-evolution reperatoir: the theory of
evolution does NOT require functions and other characteristics to spring 
into existence in completly final form.  Dawkins makes this point very
forcefully in The Blind Watchmaker.

: 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?

Why should it be?  I thought we had agreed that genetic drift, which is
inherently neutral, is a source of evolution?

: I am not sure how you could observe new function evolve (I'm not
: talking about observing functions being selected for, which I have
: observed many times myself).  So are you saying these people knew for

One day, people are alive.  The next day, they die.  Why?  Because the
bacteria in their bodies have developed the function of surviving
massive doses of a common antibiotic.  Isn't that what you're after?

: sure that the genes with the mutations that had these functions didn't
: already exist in ALL the animals in their cattle, and that they
: weren't just selected for?  

I don't understand your objection.  Being selected for changes the
frequency of this character, and THAT is evolution.  If you're trying to
pin down the exact moment at which a trait enters an individual in the
population, then you may be on a fools errand.  Traits are often adapted
and co-opted.  For example, genes which code for one protein in
hemoglobin may silently duplicate, and only over much time will that
duplication develop some functionality.  It's pointless to insist on
isolating the original duplication event, because it was silent.

: 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?

perhaps this is exactly why I'm objecting to your use of the word
"evolution", eh?  It sounds to me that you mean "mutation" by
"evolution".  The important point is that mutation without selection is
not a particularly interesting concept, from an evolutionary
perspective.

PS--I'm going to have to back out of this thread.  I just don't have any
more time.  I have enjoyed the thoughtful, honest discussions (like the
one I'm responding to).  Ciao!
--
James A. Foster			email: foster at cs.uidaho.edu
Laboratory for Applied Logic	Dept. of Computer Science
University of Idaho		www: http://www.cs.uidaho.edu/~foster

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