LUCA, is a single event sufficient or are many necessary?

Faith & Science Conversation
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LUCA

For a biologist to address the details of the OoL, he/she typically approaches it using only natural chemical processes that could create a form of life (there are many definitions of what life is, but for now let’s just require it to be cells with metabolism that can utilize substrates to create and utilize energy, can reproduce and can evolve). This is called abiogenesis. It would mean that life arose from non-living matter. The details I am interested in are unrelated to whether (or not) it arose naturally or with divine intervention. So let’s just for the purpose of conversation, assume that it does not matter. We KNOW that it did happen, so now let’s move forward to details and discussion.

I’m searching for scientific evidence to support a clearer picture for the transition of the first life to what we have today. For that purpose, it doesn’t matter if God did it, or lightning struck a soup of organic compounds, or hydrothermal hot vents on the bottom of the ocean spit it out. So to my question:

  1. Was it a single cell of life, one time only, that then reproduced billions of times to evolve into all of the forms of life we see today? If so, it could have mutated along the way such that altered DNA and/or RNA created either new genes> transcribed into mRNA> and thus new proteins, or just different controls/epigenetics on the genes already there. Or was it…
  2. Hundreds/thousands/millions of life forms, each of which could evolve its own way, in its own unique environment, to enjoy selection and reproduction advantages and thus evolution?

The complexities have been hashed and rehashed forever by both the lay believers and biological evolutionists, astrophysicists, philosophers, mathematicians, archeologists, and anthropologists alike. To have life, there must be membranes to isolate and protect the cell, electron transport schemes to provide energy, heritable material for progeny, and cellular machinery capable of enzymatic catalysis of the processes that create, correct and replicate all of this. That is a hugely complex schematic that had to exist no matter what the original life (or lives) was. Nevertheless, it did exist at the beginning, no matter who or what was responsible for it. Is it necessary that something that complex begins millions of times, or is only once sufficient?

If it was one cell (and only one time), could that one cell account for the diversity of all plant, animal, archaeal, bacterial and fungal life we have today? Are there genomic data to support or refute that possibility? Many researchers point to the origins as pointing to a single cell at the bottom of the ‘tree of life’, but they rarely spell out whether there might have been multiple beginnings, each with its own possibilities for evolution. They refer to a last universal common ancestor (LUCA) but stop short of saying there was only one LUCA. Was there a LUCA for the 3 domains of life, or possibly even multiple LUCAs e.g. for each clade/genus/species of each domain?

To narrow the question and force us to focus on the two possibilities, I have intentionally left out other important requirements, such as the elements of our periodic table and their evolutions since the H and He of the Big-Bang 13.8 Bya, as well as the unique circumstances our planet finds itself in regarding gravity, atmosphere, water and proximity to our star. These are details for a different discussion, one about the probabilities of it all happening at all. I’ve also ignored the possibility that our life was seeded from another planet, since the same question would apply to that source. My question begins with the stipulation that it WAS set in motion by one of two ways without regard to which was the proximate originating author: natural or God.

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I’ve got to run right now but just as a hint of where I’d like to go with this, life is a set of self perpetuating chemical processes. Organic chemistry is still chemistry. I suspect that many of those processes existed more fleetingly in the environment before the advent of cell membranes. Those chemical processes were still of the organic kind before they were contained by organisms. Of course I’m speculating and am not quite old enough to have witnessed it directly.

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Interesting question, but I see know way to know the answer. I would expect multiple false starts before one dominated, but no way of knowing.

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I don’t think the calculations are anywhere near so precise as to nail this down to a single individual. But yes, the point is certainly that individuals exist such that all are descended from that individual, but NOT that all are descended ONLY from this individual alone.

I think we are talking about a continuum, where the various features of a cell are added in a process of pre-biotic evolution. Thus it would be like drawing a line in the sand to say that one was a cell and what came before was not a cell. We don’t usually define a cell by one single feature but by a whole collection of features.

Talking to the “old guard” such as Dawkins in the past, it does sound like they are talking about a single cell forming by accident and then reproducing. But his expertise was evolution and not the origin of life or pre-biotic evolution.

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Understand and agree. If we modify slightly the assumptions for LUCA to mean that she would have all necessary tools (a cell, informational nucleotides, functional genes, heritability, energy production), then it seems reasonable to intuit that the “continuum” and “adding features” description is not relevant and could be bypassed enroute to the true LUCA. At that point, we have all that is needed for any and all life it seems.

Genomic research, in the search for common, universal genes found in all genomes, currently has apparently resulted in the finding of ~355 genes belonging to LUCA. Is this sufficient to move our logic toward a single cell, or must we still assume that this same or similar “cell” came about and just happened to have these same sequences of nucleotides? In fact, certain “long genes” seem not to have shared material and lend credence to a single ancestor for archaea, bacteria and eukaryotes. This ( Looking for LUCA, the Last Universal Common Ancestor | News | Astrobiology ) from NASA’s Astrobiology division found this by eliminating most of the 11,000 genes they considered candidates after correcting for possible lateral gene transfers. It was from this research that they concluded hydrothermal vents as the source. Why couldn’t all 3 domains evolve from this cell, finally formed to have all of the necessary equipment?

But doesn’t the original premise and cellular division stipulate that even though there are many ancestors, they MUST converge toward a single parent?

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Possibly, but LUCA comes after all false starts, doesn’t she? So once we have a true LUCA, must there be others in order that we create the life we see today?

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Nope. Tracing back a particular development may lead one to one ancestor while tracing back a different development can lead back to a different ancestor through a different lineage.

Even with prokaryotic cells there is an exchange of genetic materials between cells. Ancestry diverges rather than converges even in their case. And with eukaryotic cells, descendants are not just a product of cell division but also sexual reproduction. Try looking up sexual reproduction in amoebas.

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I’d go with not one LUCA, but many … just to annoy atheists.

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Why do you think that should matter to an atheist in particular?

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The available data points to a single common ancestor of all known life (bacteria, archaea, and eukaryotes). Of course, other branches likely died out. Is there a more remote single origin of all of those on Earth? Maybe; it’s hard to imagine how we could tell. But multiple independently-arising lineages would not be surprising under non-intervention-style abiogenesis; I don’t think it particularly would tell us much one way or another on other questions.

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I don’t understand. What do you mean others?

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You need to read Nick Lane’s The Vital Question.. The proximal originator of all nature is nature, with one possible exception. There is nothing spooky about nucleogenesis or the Earth; this is all the sharpshooter fallacy on to of the fallacy of incredulity.

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I think it’s just the idea that there would be one hypothetical common ancestor for all life on earth. Life could have started up more than once but even so the question is whether there could be multiple lineages continuing still. Doesn’t make much difference to me one way or the other. But it is at least a bit interesting to know if that can in fact be determined.

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Tracing backwards, from a single person, clearly diverges. The number of ancestors increases with the square of the previous number of generations (corrected for marrying 2nd cousins, of course). But the issue is not for a single person, but for a population. Then the opposite occurs, doesn’t it? We converge as we get closer to the last common ancestor. Two people, X and Y, on an isolated island, over 30 generations of having 2 kids, produces 1,000,000,000 people, any one of which could trace his ancestry back to converge onto persons X and Y who would be their link to finding LUCA. Person X and Y similarly could do the same. That is my intuition about tracing any population back toward their LUCA. So as each limb of the tree branches, a newer LUCA appears, but he has an ancestry also, etc etc. Same for Giant Sequoias ancestry and E.coli. Each clade converges, but I don’t know if the evidence is that there is ultimate convergence to a single set of parents for all life.

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By others I mean other LUCAs. In other words is it necessary that there be multiple successful attempts at living cell origination to evolve into our 8.7 M species today. Or did it all start with one single living cell that evolved? I am assuming that we agree on the issue of evolution. And also I am ignoring the debate of what is responsible for creating that first living cell, be it God or by natural events.

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There is only one lineage extant for all life on Earth now, as has been the case for 4.5 bya, in the Hadean, and no hint of new starters since. It’s almost certainly impossible that there could have been from then and time does not heal that situation. It actually makes it worse.

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Ironically, I think one LUCA deals them more fits, since their prejudice is that hydrothermal vents could easily have created millions of “starter cells” to then evolve.

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Are you thinking about the data from Astrobiology of NASA? It would make sense to me if the common denominator of ~355 genes necessary for any life implies a common ancestor.

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All life on Earth for the past 4.5 ga is from (a single - that’s redundant) LUCA. That’s what the U means. God is utterly unnecessary to explain that and all layers of causality. All. It is logically possible, permissible to posit that He is, nonetheless, the first layer, despite being unparsimonious.

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In fact I am, but it is almost entirely dealing with the complexities of a living cell and how the organelles could have been acquired. Especially in the time-frame allotted. I cannot find Lane dealing with the proposal that we necessarily only required a single LUCA or many were required.

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