Hi Thmsberry,
quote:
I have read that those who support several live ancestors make the assumption that they are all members of the same species. Yet, all current evidence points to the fact that the oldest known live organisms on this planet reproduce asexually. In addition, all current evidence points to the fact that the oldest known live organisms were without a nucleus. Doesn't these scientific facts make the idea that they were all of the same species ridiculously ambiguous and basically meaningless and unprovable?
You've stated things a bit unequivocally ("all current evidence etc...").
First, they're not scientific facts but informed hypotheses.
Second, in the general case, members of the same species can be assumed to have a common ancestor. When this is not the case it means the same species evolved more than once. This is probably only possible in any meaningful sense for single-celled organisms, and all it would mean is that the same or very similar genetic accidents happened more than once, resulting in organisms with equivalent genomes. I'm speculating, since I've never myself read of anyone seriously entertaining this possibility, but that doesn't mean anything.
One of the views receiving attention these days is that gene sharing was very common among early life, and this is described in some detail in an article (that I referenced once before, and I see Larry mentions it, too) titled
Uprooting the Tree of Life by W. Ford Doolittle that appeared in the February, 2000, issue of Scientific American, and here's a diagram from that article (click to enlarge):
We've already discussed that BSC is mostly appropriate only for the more complex lifeforms like mammals, and so it certainly shouldn't be applied to a situation like that represented above involving single-celled organisms. Species distinctions can be more difficult to make when organisms are single-celled and similar, but the DNA tells the truth. We can certainly make no specific species distinctions about postulated evolutionary ancestors, but the above diagram derives from DNA analysis of modern organisms. It is speculative, and if that's a synonym for "ridiculously ambiguous" then fine. It's certainly also unprovable, as is all science, but it
does have evidentiary support based on DNA and so definitely is not "basically meaningless."
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Asexual organisms alone have an ambiguous species definition. Add to that the fact that Archae show no consistent correlations between morphology and known phylogeny and their phylogenies even intersect with organisms of other domains. Thus, How would it ever even be possible to determine if the early live ancestors(as in a population) were of the same species?
I think you mistake what is being attempted. It is understood that we can't know what the specific ancestors were, but we can certainly draw hypotheses concerning possible scenarios. Current work is identifying and characterizing the reasonable possibilities indicated by the evidence available, that is all. But it is understood that there can never be any definitive evolutionary tree because there is simply insufficient evidence. Time has destroyed most of the evidence, and scientists just have to make do with what's left.
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If the first population of life contained multiple kingdoms. Such as the diversity in Archae and Eubacteria currently shows. and If this diversity does not fit in a nested hierarchy that corelates to the genetic diversity. As the diversity in the Archae and Eubacteria currently shows. Then the first population was not one species. It wasn't even monophyletic.
By the time you wrote this Larry had already referenced you to Doolittle. It is already well understood that early life might not fit a neatly nested hierarchy.
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This basically leaves the premise that all life on this planet can be traced in part to a population of a single domain.
Thus, the individual organism and/or species idea is not a supported one. And this is one of the major aspects of the current ToE.
The ToE is just a framework of understanding that unites Darwinian concepts like descent with modification and natural selection with a genetic foundation. The ToE never axiomatically held that all life descends from a single original cell. That's just a once-common perspective that fit within the framework of the theory, as do the newer perspectives on this topic. It was not a major aspect of the theory, but rather just a possibility permitted within the framework of the theory.
The possibility of all modern life descending from a single cell is consistent with the ToE. So is the possibility of all modern life descending from a community of gene-sharing cells. Changing preferences within the scientific community for one over the other do not require any change to the encompassing theory.
--Percy