But that’s the ancestor Theobald is talking about. By the nature of phylogenetics, we can know little about what happened before the most recent common ancestor. And of course nobody, including Theobald, is talking about a single organism. It’s at least a population.
Not if by “one” you mean a single individual.
Could you put out those statements so we can look at them?
What sort of systems are you thinking of here? Presumably there must be a single origin of the genetic code. I suppose there could be multiple origins of RNA life that might combine RNA genomes. What else were you thinking of?
Maybe so, but he used the expression “single species,” which doesn’t convey the image of a cluster or tangle or bush of species swapping genes. So to the normal reader of English, he seems to mean what I meant. However, I concede that in a journal like Nature, he might be writing in “shop talk” and that words might mean something different to specialists than they do in everyday English conversation and writing.
I don’t, either. I was just trying to find out how you defined the term, what you had in mind by it.
That may be true in the discussions of the past 30-40 years. I doubt if it’s true about what biologists were thinking from the 1900s through 1960s. If you come across counterexamples from that period, let me know, and I will revise my notion of the history of thought for that period accordingly. In any case, that certainly remains the popular understanding of the universal common ancestor (forget about the addition “last” for the moment). You can still see it in Star Trek: The Next Generation, when “Q” takes Capt. Picard back to Darwin’s “warm little pond” where the one-celled organism has just emerged out of the primeval ooze, and Q informs Picard that all the future races of living things – including humans, Romulans, Klingons, Vulcans, etc. (which is part of the moral message of the episode, that our political differences are petty in comparison with the origin we share in common) – take their birth from this first emergence of life from non-life. This was the view implicit in every science fiction and popular science account of evolution I read or watched, growing up in the 1960s or 1970s. And those writers were not always journalists with no science background, either. Some of them were people like Asimov etc. well educated in the life sciences. So the idea was around.
You are talking about later refinements to the original idea. I don’t say the refinements aren’t warranted, but the point remains that if, as you say, the basic rules of the genetic code, the basic protein-DNA setup, hasn’t changed much since it was established, then the basic genetic code wouldn’t be much different in the first living thing that had a DNA-protein setup than it was maybe hundreds of millions of years later in some “tangle” or “bush” of intertwining, DNA-exchanging organisms. So if all life today is descended from that “bush” or “tangle”, then it is also descended from the first protein-DNA type of cell that preceded that tangle. That is, it is also descended from an even earlier single organism. You seem to be satisfied with going back to the great-great-great-(x 10,000)-grandparents of modern species; I’m interested in who their great-great-great-(x 1,000,000)-grandparent was. I don’t see why the idea of an original single organism, earlier than the “tangle” or “bush”, has to be ruled wrong in order for the affirmation of a later “population” or “bush” or “tangle” to be right. So what are we arguing about here? Just the meaning of the term UCA?
If that’s all we are arguing about, then I could have rephrased my original point, way up, to take that into account. My original point was that many 20th-century biologists supposed that if you traced all lines of descent all the way back (as far as you could possibly go without hitting non-life), you would eventually reach a single organism that was the granddaddy of all the fungi, plants, animals, bacteria, etc., but that some biologists now suspect that life may have had more than one start from non-life, which means that after navigating backwards through the bush or tangle, one would then have to follow several parallel, non-converging paths back to several distinct origin of life events. I don’t see that this is difficult to grasp; it’s simply following the logic of what is being asserted.
I believe that above you made the point that it is unlikely that there could be several independent starts to life, on the grounds that different types of life with different codes would be incompatible, and could not cross-fertilize, etc. Yes, but what if they didn’t have different codes? We certainly can’t – given how little we know about the origin of life – rule out the possibility that the chemistry and physics of simple molecules and the way they aggregate into more complex ones have a natural “tilt” (I’m not speaking about God and miracles here, just tendencies based on molecular geometry, energy and stability considerations, and other factors) toward a protein-DNA type of life. If there is such a tilt, then independent starts of life would be expected to produce similar results, and would not rule out later crossovers between lines that were originally distinct.
I don’t have any more time for this discussion, so I may not reply further, but you are welcome to comment again if you like.
My point was that your statement about what the Bible teaches has no weight whatsoever, unless accompanied by passages and exposition. It’s sheer assertion. In the absence of any exposition on your part, I’ll assume you made the statement just to be provocative, and not because you had the slightest amount of evidence or reason behind it.
Yet I know of scientists, even one in your own field, who regularly bragged (and insulted people) while hiding behind pseudonyms on BioLogos and other websites, and I didn’t hear you objecting to that. Nor do I hear you objecting to the use of a pseudonym by T. aquaticus or by certain other people here.
I mention it because he’s referring to the most recent common ancestor, which you didn’t realize, and you have also confused “single species” with “single individual”.
You are free to think whatever you like in the absence of actual evidence. Still, one might hope for some support of your contention. And you are seriously using Star Trek to support your claims about science? Even you should be able to see how absurd that is.
No, that just doesn’t follow, so “that is” is just plain wrong. You still have no support for this claim.
Sorry. We can indeed rule that out even given what little we know.
I know the difference between a species and an individual. But in one-celled organisms, which at least at first must have reproduced by some version of mitosis (what other option did they have, before meiosis was invented?), all the members of the species would go back to one individual, if you rewind the clock to the moment before the first split. So if Theobald really believes that at one time, billions of years ago, there was only one species (not several interchanging species) on this planet, then he has no choice but to postulate a single individual as the founder of that one species.
It does follow; in fact, it’s logically necessary, by the meaning of the terms involved, so further “support” is not needed. If A is the great-grandson of B, and B is the great-grandson of C, then A is descended not only from B but also from C. It’s implied in the meaning of “descent.” Every one of the gene-exchanging organisms in your “tangle” or “bush” or “population” had an ancestor, and eventually, as you wind back the clock to the origin of life (which you have just argued must be unique, because otherwise there would be incompatible genetic codes), you must come to a single common ancestor. Yes, this common ancestor will quickly multiply and become a “species”, an aggregate of individuals with the same characteristics – it will be a particular species of bacteria, or proto-bacteria, or whatever you decide to classify it as, and the species will be represented by millions of individuals in short order. But all of those individuals were generated from a single individual – and that individual – by your own argument that a single genetic code implies a unique origin of life – will necessarily be the ancestor of all future species, including those now extinct as well as those now extant. This is a matter of logic, and I need the approval of no biologist to be sure that it is correct.
Since you are the hotshot molecular biologist here, claiming great expertise in evolutionary theory (though as far as I can tell it’s not your field), and have much faster access to the scientific literature than I do – I would imagine that there is a large science library at your university, crammed with books and journals, and that you can access much of it online even from home – it should be easy for you to disprove my claim by citing me biologists who were talking about bushes and populations etc. and denying single-organism origins, from the 1910s, the 1920s, etc. all the way up to the 1960s. I have read lots of the history of evolutionary theory. I’ve not yet read anyone from the first part of the 20th century who doesn’t endorse or at least imply the existence of an original single organism ancestral to all. Show me the money, show me that the idea of a single-organism origin was not the general view touted at the time, and I’ll change my view.
Of course you know that I didn’t claim that Star Trek represented technically precise modern evolutionary biology. I claimed only that it represented a longstanding popular conception of evolution (one I can verify as longstanding, being older by a considerable amount than a number of people posting here), and that conception wasn’t invented by science fiction writers or journalists, but borrowed by them; it had antecedents in the writings of the scientists themselves, starting with Darwin, who thought that probably there were only a handful of starting-points (e.g., a common ancestor for all plants, and another one for all animals) and that there might have been a single starting point for plants, animals, and all other kingdoms. Certainly by the time I started reading about science, Darwin’s caution about plants and animals had been dropped, and every biologist or paleontologist I ever read asserted as undeniable fact that plants and animals all sprang from a common one-celled ancestor. I read no scientist who asserted that life had several separate origins, one from non-life to plants, another from non-life to animals, another from non-life to fungi, etc. I believe that this “single origin” view was the prevalent view among professional evolutionary theorists for at least the first half of the 20th century. Prove me wrong by a selection of passages from 1900-1906, and I will modify my view. You are a phylogeneticist and therefore should be able to access all kinds of books and articles on evolutionary theory from the period I’m talking about. I suspect that the history of evolutionary theory (more than 20 or 30 years past, anyway) is not your academic “thing,” but still, you are in a position to assemble the relevant material faster than I am. I have inadequate online access to do a proper historical survey and cull examples from the mass of material. From the books and articles I have read, on paper and online, my generalization seems correct, but I am open to refutation from a larger body of material.
