On Thu, 12 Jun 2003 02:45:18 +0000 (UTC), Michael Ragland
 
wrote:
> On Wed, 11 Jun 2003, Larry Moran wrote:
>> On Wed, 11 Jun 2003, Michael Ragland  wrote:

[snip]

>>> Most genetic variation is in the non-coding region and is not a result
>>> of natural selection but in the coding region I would argue natural
>>> selection plays a much more important role than random genetic drift. 
> 
>> Well, I guess this depends on what you mean by
"important." If you're
>> referring to frequency then I'm afraid you're going to continue to be
>> "disturbed" because most changes in the coding regions
of genes result
>> from fixation of neutral alleles by random genetic drift. 
> 
> I stated in terms of adaptive evolution the coded region is more
> important than the non-coding region. You responded, "Yes, this is
> probably correct." When it comes to the coding region what role has
> natural selection played. You've acknowledged it probably plays a more
> important role in the coding region than the non-coding region but you
> state most changes in the coding regions of genes result from fixation
> of neutral alleles by random genetic drift. I may be mistaken but when
> it comes to morphological evolution rather than molecular evolution
> can't a strong case be made changes in the coding regions of genes are
> of less importance?

Your question is a bit confusing - is there a typo?

Let's consider "morphological evolution" to see if we can reach agreement
on what we're talking about. When I think of "morphology" I think of
changes in the external appearance of an organism. This may not be the
only way to define morphology but let's go with it for the time being.
Okay?

Over the course of several billion years of evolution there have been
significant changes in the morphology of species. Oak trees sure look
different than elephants even though they evolved from a common ancestor.
Such changes in morphology are not confined to large visible organisms
since you can see similar changes when you examine different species of
bacteria and different species of single-celled eukaryotes.

The evolution of morphological changes, at this scale, is probably due
to all kinds of changes at the molecular level. This includes the 
evolution of new genes and changes in the coding regions of existing
genes so that they encode new functions. It also includes changes in the
non-coding regions of genes so that the protein products are produced
at different times or different rates.

I'm not sure how we can quantify the relative importance of all the
various mutations that have given rise to morphological change over
millions of years. It depends on your perspective. Are the mutations
that gave rise to the characteristic shape of pine needles more
"important" than those that distinguish red pine (clusters of two
needles) from white pine (clusters of five needles)? We need to answer
such questions before deciding whether changes in the coding or non-
coding regions are "more important."

However, knowing your bias towards human evolution, it's safe to assume
that you are interested in fairly recent morphological changes in the
human lineage. Are the morphological differences between humans and
chimps, for example, due mostly to (adaptive?) changes in coding regions
or in non-coding regions? In this case, the morphological changes are
most likely due largely to changes in non-coding regions that alter the
expression of genes required for development. Is this what you meant?

Whether all of these changes are adaptive (i.e. fixed in the population
by natural selection) or not is an open question. Some of them are,
such as an increase in brain size, while some of them may be non-adaptive
accidents of evolution, such as changes in the shape of the ear. Most
people, including many evolutionary biologists, prefer to advance
adaptive explanations for morphological change - especially when it
comes to human evolution. Sometimes these people do so because they
are unaware of the importance of alternative explanations such as
fixation of neutral alleles by random genetic drift. In other words,
adaptive explanations (sometimes called "just-so" stories) are often
seen as the only possibility by those who do not have a complete
understanding of the ways in which populations evolve. My goal here
is to make you aware of these other possibilites.

>>> For example, only a fool would suggest the trait of aggression is to be
>>> found in the non-coding region. This was a positive trait selected by
>>> natural selection. 
> 
>> Some of us fools are skeptical about the existence of an
"agression"
>> gene and skeptical about whether it would be selected if it existed. 
> 
> Skepticism is healthy. I can see where a geneticist might have
> difficulty with labeling a gene(s) as aggression. There is a gene for
> shyness, novelty, etc. It is my firm conviction such a fundamental and
> powerful trait such as "aggession" has a biological basis. I think to
> believe otherwise is not healthy skepticism but foolishness/denial. 

Of course, behavior has a biological basis. Differences between the behavior 
of oak trees and elephants is obviously due to differences in their genes.
That's not the problem.

> I've never stated there is an "aggression gene". I think
only a dimwit 
> would believe that. I think there are many genes involved in aggression. 
> For example, we may discover a gene invoved in aggression in the future 
> but this does not mean we have a full understanding of aggression and all
> the genes responsible for it. I don't know why you should be possibly
> skeptical if aggression genes would be selected if they existed.

The word "aggression" defines a particular behavior. We are interested
in knowing whether this particular behavior is a consequence of having
a brain or whether it is independent of all of the other things that
go along with being intelligent. If you are going to make a case for
selection of "aggression gene(s)" then you have to postulate the following
senario. Assume that there can be a population of proto-humans that is 
non-aggressive but otherwise has all of the other beneficial features of
brains and intelligence. Assume that a small number of mutations can
arise in this population and these new alleles have the effect of
converting the individuals into aggressors without changing anything
else of consequence. Assume that these agressors have some sort of 
selective advantage relative to the non-agressors so that the "aggressor"
alleles become fixed in the population. With these assumptions, you
can hypothesize that agressive behavior is adaptive and has been selected
in humans. Are these assumptions reasonable?

An alternative possibility is that humans are "merely" intelligent.
As a consequence of their intelligence they can modify their behavior
to fit the circumstances. Since individual survival is an important
goal, this behavior will be directed largely toward achieving this
primary goal. Sometimes this might require aggressive behavior but most
human societies seem to prefer cooperation if given the choice. I happen
to live in a society where individual aggressive behavior is much less
prominent than what we see in the average chimpanzee tribe but I doubt
that's due to differences in our genes. If my society breaks down then
I expect aggressive behavior to increase but this is not due to changes
in our genes. 

I see aggression as just one of many optional behaviors that result from 
having a complex brain and living in a social environment. That behavior,
like most other behaviors, has not been independently selected from a 
menu of genetic choices. 

> Afterall, I wrote "If we know natural selection is not the main force in
> evolution then how can we proceed as a species to attempt to make our
> evolution adaptive?" You responded, "I don't know ... and I
don't care."
> If you don't care about this I don't see why you should possibly care if
> aggression genes would be selected if they existed. 

These are two different questions. I do care about speculations concerning
adaptation and human behavior. It's important to make sure we are using
sound evolutionary principles when thinking about such problems.

On the other hand, I'm not interested in speculations about how humans
should "evolve" in the future. Most of these speculations are not based
on a sound understanding of how we got here in the first place and how
populations evolve.

[snip]

>>> I'm operating from the assumption we're currently not an adaptive
>>>  species in our evolution. 
> 
>> I think I understand your perspective. You prefer to bring all
>> discussions of evolution around to your favorite topic, namely human
>> evolution. So, why do you operate from that assumption? Do you make the
>> same assumption for all modern species or only for Homo sapiens? 
> 
> Yes, you're correct. I do try to bring discussions of evolution around
> human evolution. However, I don't shy away from discussing other areas
> of evolution as I think my posting record reflects. Why do I make the
> assumption we're not an adaptive species? Human overpopulation,
> environmental degradation, diseases, wars, nuclear weapons, etc. I've
> written alot on this topic in the past in much more depth. Refer to my
> archive posts for further information. 

Most of your postings are based on false assumptions, in my opinion.
You are assuming that human evolution has been dominated in the past
by positive natural selection and that somehow this has ceased in the
past several thousand years. You also tend to assume that much of
human behavior has an adaptive explanation. I question all of these
assumptions.

> Do I make the assumption for all
> modern species or only Homo Sapiens? That's an interesting question. Due
> to Homo Sapien activity many modern species are threatened with
> extinction so by this criteria I guess they are not too adaptive in
> their evolution. In the absence of Homo Sapien encroachment I really
> can't say whether modern species other than Homo Sapiens are adaptive in
> their evolution. I suggest asking a biological specialist about a
> particular species. I do know, however, Homo Sapiens are not currently
> adaptive in their evolution. 

I'm glad you "know" this. Some of the rest of us are still fools.

>>> Considering how long natural selection takes in effecting changes in our
>>> coding region should biologists attempt to reach a consensus Darwinian
>>> evolution can't be relied on to affect positive adaptive changes through
>>> natural selection? 
> 
>> No, of course not. Why would you ask such a silly question? 
> 
> I don't think you're entitled to answer this question. 

Okay .... that's one way to win an argument.     :-)

[snip]



Larry Moran
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