And in knee-jerk, mind-dead fundyland straw manning the other side is so ingrained that listening becomes a lost art. But do note I don’t paint all believers with one big brush; there is nothing about your playbook that appeals to me.
3 Likes
Before the evolution of genetic code with ‘high fidelity replication’ and ‘and at least some rudimentary early form of molecular proofreading’. I.e. LUCA.
Which is of a single organism. Among many that didn’t make it.
My question was with regard to the sufficiency of
the evolution of genetic code with ‘high fidelity replication’ and ‘and at least some rudimentary early form of molecular proofreading’. I.e. LUCA.
Why bring God in to this by putting Him aside for now? Which is what you appear to be doing. He is not necessary in the slightest in the process of abiogenesis any more than He is in stellar nucleosynthesis or self-tuning.
Once we had Theobald’s (2010) and Saey’s (2010) LUCA there was no possibility of gene transfer from any other LUCAs.
For the upteentth time, my question presumes the opposite. My question (one or many origins) intentionally leaves aside the nature of the origins, but only addresses whether (or not) one original living cell is sufficient for all the life we see today. So I am NOT either “bringing Him in” nor “leaving Him out” in any way. I am simply pondering what occurred AFTER we found a cell (or cells) capable of all that we agree is necessary for it to be considered life. It seems obvious that you are simply trying to be adversarial, contentious, argumentative, petty and/or pick-nits. Why can you not offer a thoughtful opinion on the topic I posed?
Regarding lateral gene transfer, it is logical to me that this is a reasonable mechanism for cells to acquire different organelles and evolve. But my question precedes those LGT events. LGT helps explain evolution, but not whether it all began with a single living cell.
My original hope was that posing the question as I did would allow this forum to by-pass questions that disturb and divide atheists and theists. It was to get further downstream to the point that we could all agree on one thing: “It did happen” without regard to “who was responsible”. So since it did, let’s follow the evidence and understand it better.
That image helps me. It looks as though for a while whatever variety of progenitors life as we know it may have had, up until some point, sharing/stealing of genetic assets was rampant. After that it still occurs but not so pervasively. Are the reasons for this well understood? Might it be that at that point all or many organisms would have garnered the capacity to keep those resources better protected? Also how far would DNA duplication go back? Would that have existed in the ‘primordial soup’ itself before membranes separated individual organisms?
1 Like
My unreserved apologies. I’m seeing theism when it isn’t there. But… 
we are talking origins…
There is no doubt in my mind that the pre-LUCA, i.e. pre-genetic code “with ‘high fidelity replication’ and ‘and at least some rudimentary early form of molecular proofreading’”, Ur-organisms of late biogenesis engaged in gene transfer, just as all organisms do today. As per the hypotheses link.
My comment “Once we had Theobald’s (2010) and Saey’s (2010) LUCA there was no possibility of gene transfer from any other LUCAs” is based on the feeling that gene transfer from other LUCAs that all died out in the late Hadean-Eoarchean would have been prevented as as each LUCA will have had a different set of amino acids? Assuming different triplet coding bases? Which seeing that all four have been found found in meteorites would indicate not… so what other mechanisms would have blocked gene transfer from other LUCAs which died out? Perhaps none, but our LUCA dominated, out-competed them to extinction. How?
What would have differentiated competing LUCAs engaging in gene transfer? Or with sufficient gene transfer did they all homogenize to a single dominant LUCA with no more possible gene transfer from lesser LUCAs?
All the evidence is for LUCA. That is agreed. By science. Therefore how can there be any disagreement here?
The more logical mechanism is endosymbiosis.
LUCA has nothing to do with the origin of life either. LUCA would have existed well after life first appeared on Earth.
The organisms that became chloroplasts and mitochondria would have already had informational and instructional nucleotides. Also, the endosymbiotic events that define modern eukaryotes would have happened well after LUCA and the origin of life.
1 Like
LUCA would have already had the genetic mechanisms we see today, such as 3 base codons, tRNA’s, and the rest.
I don’t see why this would have to be the case. There could be a case where genetic systems and metabolic systems were split between several lineages.
I fully agree. LUCA doesn’t seem to be a good entry point for understanding how life started, only how different lineages coalesced into the trunk of the Tree of Life we see now. It could be that there were multiple origins of life where some initial life forms focused more on genetic copying and others focused more on metabolism.
Agreed…I should have said that LGT could have contributed and been one of the mechanisms for accretion of organelles.
1 Like
Not particularly thinking of NASA but of the general phylogenetic analyses on protists and eukaryotes. The shared genetic code and other similarities across all known earth life makes a strong case that the life that we see on earth all has a single common ancestor. I don’t know of any particular biological reason to think that one versus more lineages of life are more likely. On the one hand, given that the early chemistry of earth seems to have been suitable for abiogenesis to happen once, it would seem credible that it could happen more than once. On the other hand, once one lineage got started, it might take over and gobble up relevant chemicals before anything else can get a start.
A single common ancestor of all current life on earth could represent the lone survivors of an extinction event, a lineage that gradually outcompeted its rivals, merely the random point where surviving lineages converge within a broader ancestral group, etc.
Interesting thoughts. But yes I think there are some pretty obvious reasons. Purely random variation is pretty much only found in viruses, i.e. the simplest of organism. Thus it seems to be the general rule that more complex organisms require greater controls on variation because too many of the possible variations are lethal.
However this does raise an interesting thought. Is it possible that there is a stage in the evolutionary process where these strategies have some overlap? Are there eukaryotes which engage in horizontal gene transfer? Apparently the discovery that this is the case is a recent development in biology which is shedding some new light on things. It suggests a time in our ancestry where all the evolutionary developments of single celled organisms could be shared. It means that any notions of a LUCA can only apply afterwards when such gene sharing was no longer a part of our ancestry, and before that any of the cells engaging in HGT with our ancestors would be included in our universal common ancestry.
2 Likes
(a) then we agree. That’s what I meant, sorry for the ambiguity.
The evolution of genetic code with ‘high fidelity replication’ and ‘and at least some rudimentary early form of molecular proofreading’ = LUCA. Or = the nucleus organism involved in the endosymbiosis that became LUCA?
(b) I like it; endosymbiosis. To LUCA?
I assume you mean a single cell at one time as the parent of all living things today? Thus our lineage parallels (+/-) bacteria, fungi, pine trees. That has been my feeling as well, fwiw.
The best reason, logicall, to assume more than one is simply the diversity of all life. Many of us struggle to believe that our cousins are bacteria.
I suppose so. But the common theme for origins is always the incredibly unlikely sequences of events necessary for a cell to become “living”. It’s sort of like the probability issues of a monkey hammering out the Gettysburg Address on the typewriter.
Always on the table, as is seeding from alien visits. But in every case, the same question arises about the “original” parent, one time occurrence or the necessity for many.
That clearly could speed the process up a bit. Left unanswered (among the thousands of things such) is the Cambrian explosion, with 27 phyla exploding on the scene. Could HGT account for that, rather than believe in major mutations of the Hox genes without cellular death? And even accepting that possibility does little to address whether there were many “original cells” that began to exchange material, both developed and important, without the necessity for deriving it via parental lineage.
Perhaps, and if so we really have a problem defining what is meant by LUCA. Many have used terms such as Last Eukaryotic Common Ancestor or LECA to jump past the original, include much of the HGT/LGT, and move forward with evolution. Your question may require many L?CA’s to fill the empty places in the “tree of life”. I note that researchers have wide ranges for the amount of current material that could be represented by that process, and the article you linked suggests only 1%.
The wood from all the trees we know tell of, including fossil (but not coal obviously…), is from the last universal common tree.
Note that part of that may be sampling bias–we have a couple of Lagerstaetten in the Ediacaran and Cambrian, but very few from a bit earlier. Hence, some of those phyla may have appeared a bit earlier. There is also the problem that without exceptional preservation, most phyla are simply generic worms. That also makes basal members very difficult to identify.
Between the endosymbionts (organelle Ur-organisms?) making them more interdependent and compatible?
And
How many different Gettysburg Addresses could there have been? For the sharpshooter? The probability going forward was 1.
To this point, I am guided again by the forces that direct evolution, selective advantages. No matter how an organelle arrived, if it worked better that cell’s progeny had an advantage. I have found nothing to supplant basic Darwinism on that point.
And the monkeys at the typewriter, I’ve read so much written by mathematicians about the statistical odds against what we know happened actually happening (of course it did, so there is that ). It approaches one chance out of 10^90 which is like finding one atom in the universe (there are between 10^78 and 10^82, or some such absurdity). How are we to derive meaning from improbable occurrences when it actually turns out that it is 1?