What's the smallest unit of evolution?

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The 0-Logick
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What's the smallest unit of evolution?

Post by The 0-Logick » Tue Feb 27, 2007 12:14 pm

I've been puzzling over this for a while now. I know that the textbook answer to this question is 'population' but I find that answer to be lacking for a number of reasons. It might mainly because it's because population isn't a clear-cut concept.

So the question might as well be 'What could be considered to be a population?' The development of drug-resistant HIV is being used as an example of evolution. But a number of problems rise from using viruses as an example. It would basically mean that a single virus could be considered as a population by itself, wouldn't it? The same problem is with single-celled and asexually reproducing organisms.

Another problem arising from using viruses as an example of evolution is that one basic rule of evolution is considered to be that natural selection works only with the phenotype and not the genotype. But that distinction is far from clear with viruses, so much so that a viruses genotype could be considered to be it's phenotype, unless a virus' phenotype is considered to be expressed only in it's RNA-encased-in-capsid form.

When you go to RNA, the whole 'natural selection works only with the phenotype and not the genotype' starts to be hard to take at face value. Enzymes are considered to be a part of the phenotype. What about ribozymes? The distinction between genotype and phenotype start to seem a little too arbitrary for my liking...

So what do you think? Any opinions? Or sage advice? Is there any info in the net about this? Tried to look for it but simple googling didn't bring any helpful pages. I'd be thankful for any insight on this matter.

edit: corrected 'face value' and added this explanation...
Last edited by The 0-Logick on Tue Feb 27, 2007 8:18 pm, edited 2 times in total.

Darby
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Post by Darby » Tue Feb 27, 2007 6:58 pm

You're right, it's very confusing - I don't even know what a "unit of evolution" is supposed to <i>mean</i>.

I like your example of the virus - a lot of the "rules" were really developed to apply purely to diverse, sexually-reproducing populations. They don't move easily over to asexual species.

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AstusAleator
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Post by AstusAleator » Tue Feb 27, 2007 8:42 pm

First of all, good post :).

I think that you're right, about many models of evolution not fitting with virus evolution. Viruses are still evolving, but not in the same way living things do.

most of the concepts (at least the basic ones) applied to evolution (particularly ecological evolution) are designed to address living creatures.

Since evolution is not an object or composite, I don't think using the term "smallest unit" quite works. Maybe call it the most basic function? Or the most basic operating force?

I hope Canalon has something to say about this, since it's right down his alley.
What did the parasitic Candiru fish say when it finally found a host? - - "Urethra!!"

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Khaiy
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Post by Khaiy » Wed Feb 28, 2007 4:08 am

I agree with you, and the posters above me. Viruses are not presently considered alive, and so the rules of biology wouldn't necessarily apply to them. But there has been a lot of debate about that, and that point might be a good one to bring up in that debate...

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