Re: [asa] Question on molecular biology and Darwinism

From: PvM <>
Date: Wed Jul 02 2008 - 12:45:18 EDT

Sure, you stated that

'The whole discussion began with a premise:
If 65M years ago, after the Yucatan impact, the only mammals remaining
were little rodents,
what gene changes were necessary to take them from chipmunk to human?
It would seem that there would be millions of them in order to
accomplish minute changes."

s single point mutations in genes can change a whole limb, is the
observation that minor changes in regulatory parts of genes, not even
necessarily genes themselves can lead to relatively large
developmental changes. Developmentary biology is how the information
in the genes is expressed into the final phenotype and what science
has found is that development is a processes of timing, interactions
with local gradients, gravity and neighboring cells which determine
the course of development. As such we see how changes to genes, or
their regulatory regions can generate eyes and wings in fruitflies
where none normally would exist, just by switching on or off
particular gene expressions. Another example is the extension or
reduction in length of a development process, thus either maintaining
the juvenile characteristics of a species or lengthening particular
aspects of for instance limbs.For instance lengthening the arm can
happen independent of the hand which still will develop at the end of
the arm even though the shape or other characteristics of the arm may
change. Repression of the development of digits in the hand explain
the avian 'hand' versus the mammalian 'hand'.

Regulatory regions are typically short regions adjacent to genes and
their evolution may be far more important than the changes in the
actual genes. Thus we may find that the difference between us and our
common ancestors in fixed new genes can be relatively 'small' and yet
the phenotype difference can be large.

Timing in development is everything, and by turning on and off the
clock the basic bauplan can be varied significantly. That we find a
set of well conserved genes (such as hox genes) where variations in
timing of expression and location of expression can lead to relatively
large changes in the phenotype is exciting as it shows that the
original view of 'one gene per phenotype' is indeed somewhat naive.
Genes typically form networks of interactions and local conditions
determine the development.

Your statement that "It would appear that gene changes might often be
significant, and not as the evolutionary models might indicate." is
puzzling to me since genetic changes are the foundation of
evolutionary models.

What am I missing here?

On Wed, Jul 2, 2008 at 9:09 AM, Collin R Brendemuehl
<> wrote:
> I don't know where you are going. Could you clarify just a bit?
> At 11:06 AM 7/2/2008, you wrote:
>> Why would this not be part of evolutionary models? I believe it is
>> known as evolutionary development.
>> To unsubscribe, send a message to with
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> Sincerely,
> Collin Brendemuehl
> "He is no fool who gives what he cannot keep to gain what he cannot lose"
> -- Jim Elliott
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Received on Wed Jul 2 12:45:48 2008

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