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Mutliple Ancestral Proto-cell Hypothesis

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Mutliple Ancestral Proto-cell Hypothesis

Postby David George » Mon Mar 06, 2006 8:23 am

If conditions were just right to form the initial self replicating ribozyme-ish molecules and their accomanying lipid vessicles, I think that the possibility of simultaneous formation of many of these proto-cells is more probable than the formation of only one and that one surviving long enough to produce an entire evolutionary lineage. The initial presence of many proto-cells would increase the chance of survival. The evolution of sexual reproduction, or at least evolution of mechanisms for injecting and splicing genetic materials, would further increase the chances of survival by having a larger base genome. This is AstusAleator's hypothesis.I think that this can be true as we can see a lot of variation between plants, animals and viruses.May be the common factors seen in plants and animals occured as they all were formed in the same period with the same environment,molecules,etc.Probably plants proto-cell was formed first formed and the animals also formed by the side each having its own way of adapting to life.These proto-cell should have simply let molecules diffuse giving them energy they might have also reroduce asexually and possed potential immortality.Only in the later stages they must have evolved to die.Death may be considered as a mournful happening but it is very much essential for the environment.Death must be something that evolved.Astus I may not have stressed on your point but have to say I fully accept your hypothesis.
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Postby AstusAleator » Mon Mar 06, 2006 9:02 am

Well, I think you're combining two hypotheses here, the evolution of death, and my protocell hypotesis.
I'm afriad I can't agree totally with your interpretation of my hypothesis. I'm not saying that multiple ancestral proto-cells could account for the differences between organisms like plants and animals.
What I am saying is that the initial presence of multiple proto-cells would have greatly increased the chances of their continued survival, to a point at which they became complex enough to reproduce and diversify.
Moreover, according to my hypothesis, it's improbable that different protocells developed entirely different macro-lineages. It's unlikely that any extant lineages could be traced back to multiple protocells EXCEPT in the case that the protocells may have combined genetic information with eachother.
The differences between plants and animals can be best explored in taking close looks at prokaryotes and primitive eukaryotes. The endosymbiotic hypothesis seems to deal with this issue the best.

As for the evolution of death, I highly doubt that these proto-cells lived much longer than it took for them to reproduce.
I do think that at a certain point in evolution, programmed death became an evolutionary adaptation, but it wasn't there in the beginning.

ps, put the first part of your post in quotes plz
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Postby alextemplet » Mon Mar 06, 2006 11:25 am

I read a hypothesis very similar to your proto-cell hypothesis a few years ago. This one theorized that the first organisms, since they were probably little more than just strands of genetic material perhaps with a protective protein coat, might have been able to trade DNA frequently between them at a rate much higher than anything we see today. If this is true it is possible that our earliest ancestor may not have been a single cell but every single proto-organism on the face of the earth.

Well, I'm also a believer in this multiple proto-cell theory. I think it's much more probable for life to get started if it has multiple chances, and if conditions were good enough for one cell to form it certainly would have been possible for others to form too. What do you think about the RNA-world hypothesis, that life began first based on RNA and later evolved to DNA?

As for the evolution of death, I must confess to being woefully unenlightened here. Perhaps one of you could explain it in more detail or provide a link where I might research it further?
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Postby AstusAleator » Mon Mar 06, 2006 7:10 pm

Well alex, the evolution of death is a thread in the ecology forum. It's interesting, but rather inconclusive as none of us really have any authority on the subject.

I think the RNA world hypothesis is probably the most plausible scenario. I don't think it would have been RNA as we identify it today, but a very similar self-replicating amino acid.

In fact, this idea supports my hypothesis because: it theorizes that the very first molecules didn't necessarily replicate themselves, but catalyzed the formation of long random amino acids. these helper molecules would probably have each made thousands of amino acid chains. In turn, some of those may have gone on to become proto-cells.
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Postby AstusAleator » Tue Mar 07, 2006 2:22 am

Did this thread get reset?
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Postby David George » Tue Mar 07, 2006 5:09 am

I think the first Protocell would have been very simple with just having a plasma membrane with some protein content in it.And due to evolution probably it got more complex.The main doubt is how all the protocells would have been similar in structure and size.And hence how can we come to a conclusion of a common ancestor?As for my hypothesis Natural Death is not seen in the case of primitive species like amoeba,bacteria.They only die due to external factors or any attack of pathogens.So it is clear that protocell did not have any death but at some point of time the Death Factor should have evolved.This goes aginst the Wear and Tear Theory.The death factor I think should have evolved to let the species of their own race have more space.I have read that humans die due to the inhalation of oxygen.When a person get older the oxygen atoms demolish the cells gradually hence oxygen acts as a slow poison.So I think that the protocell should have been anaerobic.
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Postby AstusAleator » Tue Mar 07, 2006 5:30 am

Hmm, again I'd need to see the documentation proving bacteria don't undergo programmed apoptosis or simply degrade due to age.
This has spawned a little thought in my head though:
For cells to form multicellular organisms or colonies (plasmodial slime mold) there must be intracellular communication. Perhaps with the development of this communication came the differentiation between selfish, altruistic, mutual, and spiteful relationships. At this time, with the development of altruism, cells began being selected for deleterious traits such as programmed death.
Ohh ecology is fun. I'm going to double-post this over to the ecology thread.
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Postby David George » Tue Mar 07, 2006 5:52 am

So tell me how can cells be selfish?
Last edited by David George on Wed Mar 08, 2006 7:19 am, edited 1 time in total.
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Postby canalon » Tue Mar 07, 2006 1:00 pm

AstusAleator wrote:Hmm, again I'd need to see the documentation proving bacteria don't undergo programmed apoptosis or simply degrade due to age.


In fact they do age. They do not undergo apoptosis though...
Read that
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Postby AstusAleator » Wed Mar 08, 2006 2:58 am

Thank you for that link! Very useful.

David, cells, like any other organism, can be selfish in many ways. Ultimately, it comes down to competition over resources. The basic resources cells compete over are:
a) Space/location. They could take up more room, limiting the room of others. They could be located in a more hospitable location (shielded from predators, harmful environment, etc)
b) Energy/nutrients, they could consume more, decreasing the amount others can consume.

Really i can't think of any organism that doesn't compete in one way or another with it's kin.
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Postby alextemplet » Wed Mar 08, 2006 3:58 am

Very true, Astus. Darwin wrote that competition is most severe among members of the same species, for the simple reason that they're the only ones who need exactly the same resources to survive. So I guess all organisms are a little selfish.
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Postby canalon » Wed Mar 08, 2006 4:09 am

Some people even suggest that that there are competition between cells inside organisms, the selective pressure becoming the survival of the organism, and they explain this way the evolution of cell communication. The overall thesis developing this idea down to the genetic regulation.

In a few lines this may seem weak, but the book are available only in french as far as I know (see here for those who feel ready o read theoritical biology in this wonderful language) and make more sense than my few lines. But their theory are, to say the least, hard to put to the test, so they remain just theory for the moment.
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