Devolution (genetically speaking) - Tree of Life loops
For this discussion I would like to define devolution as the lose of genetic material.
The notion of Devolution came up in another thread. I understand that we do not see this in modern biology, at least to any significant degree. My question is why. There is nothing inherent in evolutionary processes that prevent a species from losing genetic material as an adaptation. The fact that we have a plethora of niches filled with genetically simpler organisms clearly shows that these organisms can compete. So why is it that the tree of life does not have loops?
Are you talking about say, a population of bacteria evolving into mere self-replicating molecules, or a population of humans evolving into chimps? I've wondered about that.
For this discussion I would like to define devolution as the lose of genetic material.
The notion of Devolution came up in another thread. I understand that we do not see this in modern biology, at least to any significant degree. My question is why. There is nothing inherent in evolutionary processes that prevent a species from losing genetic material as an adaptation. The fact that we have a plethora of niches filled with genetically simpler organisms clearly shows that these organisms can compete. So why is it that the tree of life does not have loops?
There clearly seems to be a direction?
I'm really not clear on what you're saying, here. Could you please rephrase your question? It would help if you could define what you mean by "information" and "loops".
__________________ We can allow satellites, planets, suns, universe, nay whole systems of universes, to be governed by laws, but the smallest insect, we wish to be created at once by special act.
I'm really not clear on what you're saying, here. Could you please rephrase your question? It would help if you could define what you mean by "information" and "loops".
Sure. I did not use the term information, but what I mean by the "loss of genetic material" is that the total number of base pairs in a genome would significantly decrease. The clear direction is for an increase or an approximate maintenance of existing levels. Note this is different from the simple loss of a trait. The genetic evidence is that traits are frequently lost while still maintaining the genetic markers for them in the genome. I don't mean for example why doesn't a bird evolve into a "lizard". Vertebrates all have about the same order of magnitude number of base pairs - about 10**9. Free living bacteria have about 10**6 or so. Why don't metazoans devolve into protists, for example? It sounds like a silly question, but based on the raw mechanism of evolution there is no reason why this could not happen - that I can see.
What I mean by loops are strictly not loops, but rather a case where the tree would kind of turn back on itself with regard to species complexity, as reflected by genetic complexity.
Are you talking about say, a population of bacteria evolving into mere self-replicating molecules, ...
Interesting question. I am even more curious why we see no proto-life "ecosystems" on earth today. At least bacteria and archaeans exist within our current ecosystems. Conveniently the most important question about life has a mysteriously missing piece.
I'm pretty sure the least complex free living prokaryote living today still has about 10**6 base pairs.
Aren't tasmanian devils threatened by a cancer that can actually spread from animal to animal, in other words the cancer cells are acting like bacteria? At the same time any analysis of the cells would show them distinctly eukaryote, the same dolphins while they have returned to the sea and taken on the streamlining of sharks, are still distinctly mammal. With the devolution idea, it is worth remembering that while speciation and adaptation involves selecting certain parts of the genome, at the same time, new genetic material is constantly being added every generation, each of us was born with about 120 new nuceotides our parents never had. Your loss of genetic material through adaptation can be seen in the divergence between human and chimps over, what is it, 7 million years, but that matches quite nicely the rate at which we see new genetic material being added.
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Aren't tasmanian devils threatened by a cancer that can actually spread from animal to animal, in other words the cancer cells are acting like bacteria? At the same time any analysis of the cells would show them distinctly eukaryote, the same dolphins while they have returned to the sea and taken on the streamlining of sharks, are still distinctly mammal. With the devolution idea, it is worth remembering that while speciation and adaptation involves selecting certain parts of the genome, at the same time, new genetic material is constantly being added every generation, each of us was born with about 120 new nuceotides our parents never had. Your loss of genetic material through adaptation can be seen in the divergence between human and chimps over, what is it, 7 million years, but that matches quite nicely the rate at which we see new genetic material being added.
Contagious cancer is an interesting idea. Are you sure the carcinogenic agent is not the contagion as opposed to the cancer itself? There are several issues with cancer becoming contagious: transmission and immunological rejection. I have not heard of this; though, it is not implausible. Technically this is not a loss of genetic material.
Where did you read about the addition of 120 nucleotides(60 base pairs?) per generation? I suppose you mean the growth of "junk" DNA. Do you have a source for your claim?
Speciation is not strictly a loss of genetic material - it may be, but usually it is not. Speciation is as much a matter of gene expression/suppression as it is the loss or gain of genetic material. Note: I'm not interested in "noise" in base pair numbers. I'm talking about long term genetic trends. The trend is very clear. Losses are minor over all. The direction is to larger numbers and increasing complexity.
Last edited by OrdinaryClay; 6th July 2009 at 10:38 AM.
I think I have a better understanding of where you're coming from now, OC. I can think of three topics that pertain to your question:
1) resource competition
2) developmental canalization
3) concepts concerning the "left wall of minimal complexity" and the "drunkard's walk"
Have you heard of the last concepts? Gould wrote a lot about them. You might try checking out his work.
__________________ We can allow satellites, planets, suns, universe, nay whole systems of universes, to be governed by laws, but the smallest insect, we wish to be created at once by special act.
__________________ We can allow satellites, planets, suns, universe, nay whole systems of universes, to be governed by laws, but the smallest insect, we wish to be created at once by special act.
I assume you are suggesting possible explanations for why devolution (as I described it) does not occur, but I fail to see the explanatory power in these subjects with regard to my question. The fact that simpler systems can compete is clearly evident by the success of simpler systems. A complex system, while certainly effective at competing, still has the higher cost of complexity. It is not apparent to me why complexity is maintained.
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