From: ingles@engin.umich.edu (Ray Ingles)
Subject: Re: Clarification on Microevolution and Macroevolution
Date: Tue, 13 Oct 92 11:35:43 EDT
Organization: University of Michigan Engineering, Ann Arbor

In article <1992Oct13.114147.5056@hsr.no> onar@hsr.no (Onar Aam) writes:

[Onar's clarification that he didn't mean evolution was a chance process
deleted]

[Onar's relplies to and discussion of the idea that an increase in the
number of genes is required for altering the original life ancestor into
a dog, etc. deleted]

 Here's how I (a non-biologist, so don't take my word for it- but then, I'm
unclear what biological background Onar has) would answer this point-

 1) Well, yeah. Dogs presumably *do* have more genes (nucleotides, anyway)
than whatever was the original ancestor of life.
 
 2) However, there is a major factor you're overlooking here- multicellularity.
Bacteria have enourmous selection pressure toward a small, efficient genome-
they can't afford a lot of junk sitting around.
 Multicellular creatures become multicellular by turning on and off parts
of their genome during embryotic development. It would be hardly surprising
if perhaps some parts of the genome were *never* turned on simply by chance-
that portion *had* an effect a long time ago, but not now. (Consider what
would happen if the genes that code for an appendix were skipped- not a whole
lot.)

 3) Indeed, it's even more complicated because there's so much junk DNA in
modern creatures. This drastically increases the 'dynamic range' you propose,
since we need not add genes to an existing species to expand the number of
active genes- just activate some junk. (Of course, it would be rare that such
an activation was beneficial, but beneficial point mutations are rare too.)

 4) Gene increase happens all the time. I understand ome species of mosquito
gained a near-immunity to a common pesticide by doubling the gene that codes
for a protein that meabolizes the pesticide-- and this happened in recent
times. Given a few billion years, genome expansion is not all that unlikely.
(Does anyone have a reference for this?)

 [deletion]

>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.

 Well, Onam, basically you need to calculate the range of phenotypes for
each possible genome of a given lenght. Then match it to the available
environments, etc. Actually doing it is left as an exercise for the reader.

>>    ...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.)
 
 As has been noted, gene increase happens commonly, and without speciation.
What is the difference between adding a brand new gene complex that does
something useful, and activating and selecting an existing but heretofore
dormant gene complex that does something useful? (I think the odds of the
second are much greater...)

>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.

 Many humans have extra chromosomes, extra genes attached to chromosomes,
and so forth. If some of them happened to become geographically isolated...

[deletion]

> 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.

 This is almost exactly opposite to the way evolution is proposed to act.
Or is that your point? I mean, the general idea of evolution is that
if the *environment* changes the species alters to fit the new environment.
This has been recently extended to note that small, geographically isolated
populations are much more sensitive to environmntal pressure and much more
likely to speciate under such conditions.
 (Again, I'm no biologist, and I'd appreciate someone summarizing that better.)

>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.

 No, no, no. you seem to think that species undergo massive changes in short
periods of time. This is not supported in the fossil record. A new species
usually looks almost exactly like an old species. Not only that, they generally
have almost the same lifestyle as its 'parent' species- slight differences,
at most.
 If the changes in environment are too great... the species goes extinct without
the chance to give rise to a new species that can handle it.
 Sabretooth tigrs appaently evolved many times; when there were herds of
really huge cattle, some cat evolved to be big and have large teeth (apparently
to quickly sever the jugular veins.) When the really big cattle died off...
so did the sabretooths, without getting the chance to become smaller and
hunt something else.
 You don't seem to recognize that there si a lot of pressure to keep new
species related to old... the more, and more major changes to DNA, the
exponentially more likely it is that something will go wrong. Small, safe
steps are the way to go.

>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.

 Yeah, but don't read too much into that. In fact, it argues against your case;lif you can go from some common ancestor to either chimps or humans, without
adding genes, just doing small changes to gene sequences...

[deletions]

>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.

 Hey, Im a chaos enthisiast too, Onam. (I also recommend that people at
least read Chaos, it's an awesome book!) But let's not get carried away.
We can't really know how chaos theory applies to evolution yet.
 For example, how could we plot a strange attractor for evolution? How
many dimensions do you think it would have? What variables, and what would
be the Lyapunov exponents? Can we give a rigorous definition that would allow
us to state, "This species is more complex thant that one"? What routes to
chaos do you think apply... bifurcation? Period doubling? What would be
the initial critical points?


>Onar.


Sincerely,

Ray Ingles                  || The above opinions are probably
                            || not those of the University of
ingles@engin.umich.edu      || Michigan. Yet.
Newsgroups: talk.origins