From: onar@hsr.no (Onar Aam)
Subject: Clarification on Microevolution and Macroevolution
Organization: Rogaland University Centre
Date: Tue, 13 Oct 1992 11:41:47 GMT

>>Microevolution are due to random changes (mutations)in the DNA-sequences. 
>>These changes may cause new traits to occur. 
>
>And what about selection?  It is the combination of variation (mutations) 
>and selection that drives evolution.
>

I was asked to come up with the PHYSICAL mechanism behind micro/macroevolution,
and so I did. Of course selection is the DRIVE of evolution, but that is
absolutely irrelevant. (I know that many will misunderstand this sentence, so I
will clarify.) Selection relies on variation to be active.( A uniform gene pool
will not give rise to selection, obviously) This variation in microevolution is
provided by mutations (random changes).




>>The problem, however, is that this is a limited way of change. 
>>Ex: No matter how many random changes that occur in a 
>>bacteria, the offsprings will not diverge severely from the 'original' 
>>bacteria. (I.e. a random change,yes, even a billion random changes will 
>>not make a bacteria into a dog.) In technical terms we might say that 
>>an organism (with N genes) is a DYNAMICAL SYSTEM which means that the 
>>organism can successfully change BUT within certain bondages. In other 
>>words, LIMITED change, or change within the DYNAMIC
>>RANGE of the system. (provided that the # of genes is constant)


Justin M. Sanders wrote:
>Just to make everything clear, no one (except the erectors of straw-men)
>claims that bacteria can turn into dogs through a billion jugglings of
>their DNA.  Ignoring for a moment that we must properly deal with populations
>contaning distributions of gene frequencies (a BIG ignoring).  The 
>argument runs like this:
>   1.  a few (maybe even one) mutations separate an "almost dog" from a dog,
>   2.  a few (maybe even one) mutations separate an "almost almost dog"
>        from an "almost dog"
>*** several steps deleted ****
>   X.  a few (maybe even one) mutations separate "almost therapsid reptile A"
>        from therapsid reptile A.
>*** several steps deleted ****
>   Y.  a few (maybe even one) mutations separate "almost original life form"
>        from "original life form".
>
>Note that each step is small and well within the constraints of your proposed
>"bondages."  However, while on the subject, please provide some evidence
>that such bounds exist and in what manner they are implemented.
>
 
Andy Peters wrote:
>Hmmm...there seem to be a couple of problems with this statement:
>  (1) the changes in the population are not random.  They are due to selection.
>  (2) those changes are exactly what many (dare I say most?) evolutionary
>      biologists believe to be the cause of speciation & macroevolution.
 

>Hmmm...*random* change?  Transmuation from a bacterium to a dog?  Where are you
>getting this shit?

I agree, random change was a bad expression. See my explanation below.


Now, let me make myself clear: I am NOT suggesting that evolution is driven
by chance although some people seemed to think I did. 

Lets make a thought experiment: YOU are the ultimate genetician and you are given
an ultimate task. You are given a DNA sequence with a range of say 100,000
nucleids which is not too uncommon in bacterias. You are allowed to arrange this 
genome ANY way you like. See what species you can come up with. (obs!limited time)
Now, you will probably have come up with an extremeley large number of species,
but you notice, however, that they do not differ extremely much from each other.
(You will for instance not have been able to make a dog). THIS (the total
number of species which is possible to make within the given limit) is the
theoretical dynamic range of the system. Of course, in nature the range is a lot
more narrow (but still very large) since there are combinations that
naturally will never occur. Have I made myself clear? Hope so.

L.A. Moran writes:
>It is not true that speciation is associated with a change in the number of
>genes. There are thousands and thousands of species of bacteria, for example,
>and they all appear to have about two thousand genes. 

Yup, and they are all approximately within the same dynamic range of the system.

Andy Peters wrote:
>Hmmm...could you tell us how to calculate the (capitalized) DYNAMIC RANGE
>of a system?

I sure wish I could. That is one of the hottest topics in chaotic and complex
systems today. I don't know. And I don't think anyone else know either - yet.
It's a highly complex task. And we have only just started to understand the
processes behind it.

>    ...could you tell us why you assume that the number of genes remains
>constant?
>

This is to ease the concept of dynamic systems. Obviously the number of genes
does not remain constant. But when drawing the line between micro- and
macroevolution this is an absolute necessity. (I'll explain in a minute.)
 
There are two kinds of change which can occur. Alterings in the existing sequences
and alterings in the length of the sequence. These are distinct of nature. And
when describing them it is important to have good defenitions to operate with. 
Before I do anything else, I will clarify these defenitions. 

For both, selection is the drive. However, the bases for selection are different.

In microevolution the basis is changes in existing genes. Any evolutionary step
which can be traced back as 'change in existing data' is microevolution. 
Ex. It is widely believed that all human races have the same number of genes,and
in essence the same genes. But there are small differences in the sequences.
These have accumulated over the years and can all be traced back as the sum of
changes in existing data. This is an example of microevolution.


In macroevolution the basis is change in the number of genes. This can either be
deletion or addition of genes. I do not know of cases where the deletion of genes
has been a superior advantage for a specie. A delition is in rule lethal or
strongly disadvantagous. (If many examples of the opposite exists I
would love to hear about it) This leaves us with addition of genes which normally
is caused by gene duplication. Since macroevolution is hard to observe realtime
there are no brilliantly obvious examples Which can easily be verified that I can
think of. But what I CAN do is to sketch the 'typical' path of evolution:


Assume that you have a specie which is adapted to the environment in which it
lives. It can then be said to be in a state of genetic stability. The specie 
remains approximately unchanged for a large amount of time, say 10 million years. 
Suddenly there occurs a new gene in the genome which alters the specie 
sufficiently to be called a new specie. The new specie is probably in the state
of genetic unstability. Therefore the selective preassure on the new specie will
be strong and will therefore undergo a time of rapid microevolution until genetic
stability once again is reached.



I will pick up again something that Justin M. Sanders wrote:
>Just to make everything clear, no one (except the erectors of straw-men)
>claims that bacteria can turn into dogs through a billion jugglings of
>their DNA.  Ignoring for a moment that we must properly deal with populations
>contaning distributions of gene frequencies (a BIG ignoring).  The 
>argument runs like this:
>   1.  a few (maybe even one) mutations separate an "almost dog" from a dog,
>   2.  a few (maybe even one) mutations separate an "almost almost dog"
>        from an "almost dog"
>*** several steps deleted ****
>   X.  a few (maybe even one) mutations separate "almost therapsid reptile A"
>        from therapsid reptile A.
>*** several steps deleted ****
>   Y.  a few (maybe even one) mutations separate "almost original life form"
>        from "original life form".
>
>Note that each step is small and well within the constraints of your proposed
>"bondages."  

What you are suggesting is that any major evolutionary change is due to the sum of
many small changes. WRONG, WRONG, WRONG. Each step might be within the bondages
(read dynamic range) but they do not alter these bondages. To come from original
life to a dog you have to expand the original bondages. This, by defenition, can
only occur by an increase in the number of genes. (If this still burns your face,
see my explanation on dynamic range) Now, there are some problems with early life
since micro- and macroevolution were more closely related then.
  We know that in bacterias there is a great overlapping of genes. Thus, it is
easy to understand how genes gradually could appear over time. This is not so in
most other organisms on earth. They do not rely on rapid replication and
therefore genetic efficiency is not a subject to selective preassure (at least
not in the same degree as in bacterias). Result: genes do not overlap to the
same extent as in bacterias. We also happen to know that most new genes occur
through gene duplication --> in steps, large steps.      
     Mr. Sanders view, if I understood him right, is way back in gradualism which 
is dead, gameover, finito.


Happily the genetic system is nonlinear. This means that a large change in the
genome does not necessarily correspond with a large change in anatomy or
features. And for that matter, a small change does not necessarily correspond
with a small change in anatomy or features. A perfect example of this is the
relation between chimps and humans. We're genetically 99% identical, but it
doesn't look like it.



>Hmmm...I don't quite see how the use of the (capitalized) words DYNAMICAL
>SYSTEM implies "bondages" (limits).  Do you have evidence for such limits?


>What Mr Aam appears to have done here is to recognize the 
>difficulty with the usual claim of Creationists that there 
>are 'limits" to evolution.  As we know, whenever they are
>asked to show evidence of such limits, or to explain how
>they are implemented, they back off and fall silent.


A suggestion for all of you who find my explanations on dynamic systems
insufficient: use a year or two of your life to study Nonlinear-,Chaotic-,Complex-
and Dynamical systems. Then come back and discuss with me. Certain comments
indicates that certain people knows NOTHING about the topics I mentioned.

If a whole course is too much of a challange, try out the easy classic "CHAOS" by
James Gleick. It's an elementary and popular introduction to these topics.

And to all evolutionary biologists who doesn't know anything about dynamic 
systems: you are out of date. Dynamic systems are essential to the understanding
of life and its evolution.





I need a brake. I'll continue my explanations on the general increase in
complexity in my next letter. So read on...


Onar.