From: onar@hsr.no (Onar Aam)
Subject: Re: Clarification on Microevolution and Macroevolution
Organization: Rogaland University Centre
Date: Wed, 14 Oct 1992 08:43:09 GMT



Thankyou, Ray, for intelligent remarks.





> 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.)

If you read my text more carefully you will see that I stated that
multicellular life did not have the same selective preassure on efficiency as do
bacterias. This is effect the same thing you are saying.



> 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.)

Junk DNA is largely a biproduct of evolution. Much of it is pseudogenes, eroded
genes left over after a geneduplication.



> 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?)


This is exactly what I am saying. Although I never said that geneduplication HAS
to have great impact on the species. In most cases it does not. (Hence all the
junk DNA)



>> 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.)


Again, what you say is absolutely true. I never stated WHY it happened, I merely
stated HOW it happened. Thus, my statement does not contradict yours, does it?



> 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.


The fossil record supports long spans with no (read small) change and then
sudden change. It is called Punctuated Equilibrium. (the change need not be great)


>>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...

You are right again. I mentioned that to show that small changes (like a mutation)
could produce immense effects. An interesting thing to philosophise about is
whether chimps and humans can produce firtile offsprings. (Not under natural
conditions, that is. Some parts of the genomes need to be fixed a bit.) And the
scaring thing is that they probably could...



> 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?



Ray, I am sure that you know that biological clocks are governed by chaotic
mechanisms. Some of these have already been well mapped. That evolution is also
governed by chaotic mechanisms is also fairly well detected - and for the same
reasons. Biological systems (cells,organs,organisms etc.) are all
"far-from-equilibrium" systems; they need a constant flow of energy to retain the
potential that drives them. Take away the energy (food) and they die. An analogy
can be produced for evolution. Life as a whole is ultimately a
"far-from-equilibrium" system with its main energy source from the sun. The
energy is expressed in form of natural selection. If a gene is subject to
selective preassure then it will be preserved (potential retained). If not then
the gene will erode (die). This system is clearly a nonlinear process. And you
yourself stated the problems: we don't have a clue to how evolution "really"
works. That is perhaps some of the greatest tasks in biology in the future. Heavy
research is needed. And therefore I don't have the capasity to answer your
questions.




Onar.

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