Can all of life be traced back to one single molecule that was the first living organism?
The first living organism was not a single molecule. You can get some pretty impressive organic molecules, but none of them is complex enough to be considered “alive” by itself.
That said, though, yes, all known life forms are derived from a single common ancestor. We know this because all life uses the same genetic code: The same sequence of DNA will produce the same string of amino acids, in all known organisms. The odds against this happening by chance, without a common ancestor, are combinatorically (which is far beyond astronomically) long.
that’s pretty cool, but just to be clear, it is not 500 almost life molecules that combined with 700 other almost life molecules and then in some corner of the ocean you had “life”, you are saying that ALL of life can be traced back to one SINGLE organism???
Well a molecule can’t be a living organism, but if you substitute a more generic word like entity, I’m reasonably sure the answer is we don’t know.
Note also there are at least three distinct ways it could have happened. I’d guess the way you’re thinking about it is life began once and everything now living descended from that one entity. It’s also possible that life began more than once, but some lines were out-competed and died off. And the living line was not the first. Third, life could have begun more than once and things now living are mergers of different lines so were only partially from the original life. For example the mitochondria found in most eukaryotic cells (the kind most commonly associated with living things in layman’s terms) are the power plants of cells and they have their own DNA (which we get only from our mothers) that is distinct from cellular DNA. One theory is that the mitochondria were originally independent bacteria that were absorbed into the cells.
hmmm… ok, but if there were competing lines, can we still say, well every living ting, every rabbit, human, tree and bird, all had one SINGLE ancestor… even if that ancestor combined with another, is there a bottle neck where everything living now, can be traced back?
Chronos, you probably know this better than I, but I thought that DNA didn’t code for amino acids in the sense we normally use that word, but that portions of DNA (or RNA maybe) were physically shaped in such a way to push amino acids together in the right way. If that’s true then the “code” for a amino acid can’t be arbitrary sequence of DNA “letters”, but must be a specific, or at least, a limited number of choices.
I think this is basically right, but mitochondria and their role in the emergence of eukaryotic cells do not have much to do with it, and are not a very relevant example. Eukaryotic life did not show up until a very long time after life first appeared, and there was a heck of of evolution going on in between.
I am not quite sure what you are saying here, but probably, at the very beginning, there was a stage at which the line between life and mere complex chemistry wasn’t very clear. (Of course, we can only really speculate about what happened, anyway.)
If you mean DNA as it is now, no, I don’t think that is right. As far as we know (which admittedly, may not be very far), the genetic code as it exists today is pretty arbitrary, and with a few minor tweaks you could reset any DNA codon to code for any amino acid. (Of course, an altered code can’t evolve naturally, because it would inevitably involve a deadly, completely non-viable mutation.) Maybe, at some very early stage, things were a bit more like what you suggest, but, first of all, it almost certainly wasn’t DNA originally, but maybe RNA or TNA or some other nucleic acid type of compound nobody has considered yet, or perhaps the original self replicating molecules were more like proteins, and nucleic acids came along later as a sort of backup recording. But the fact is we don’t know and can’t know for certain.
Life could’ve been a replicating molecule, it could’ve been a self sustaining chemical reaction (one that possibly occurred near thermal vents where the energy of the vents acted as a form of food and the porous rocks acted like cell walls). It could’ve been a chemical reaction that created a pool of organic molecules. You likely need among other things an energy source, organic molecules (you may not need this though), a replicator and some kind of membrane to have the origins of life.
I don’t know how certain scientists are yet, but metabolism first and replicator first seem like the most likely theories for the origin of life 3.8 billion years ago.
However our most common ancestor is likely younger than that. For example, homo sapiens have been around for 200,000 years but all of us can trace our lineage to a man who lived 60,000 years ago and a woman who lived about 180,000 years ago. The others are extinct.
As others have said the genetic sequence in mitochondria are different than in most other cells, implying mitochondria were once a competing genetic line that went extinct (or are just rare and our genetic sequencing tools haven’t found them yet). So looking for the origin of life and the youngest common ancestor of all surviving life are not the same.
bolding mine
I’d edit that to say in almost all known organisms.
The genetic code is almost universal. In a very few organisms certain codons are read differently.
No, as njtt mentioned, the genetic code (the table of codons that code for each amino acid) is largely arbitrary. For each codon (i.e. sequence of three nucleotides), there is an adapter molecule called transfer RNA that binds to a particular amino acid and presents three nucleotides to match the nucleotides of the codon. It is quite possible to design artificial tRNAs to manipulate the genetic code more or less at will and, indeed, this is one line of research now being followed in the field of synthetic biology. One goal is to rewrite the genetic code in a synthetic organism, then start introducing new amino acids that do not occur naturally.
Well. yes, but it is misleading to overstress this. The code is exactly the same in the vast majority of known cases, and where there are differences, they are very minor, with the vast majority of the code remaining the same.
The question is, how did we get from simple molecules to the complex collections we recognize as life? If you could answer that question, you get a Nobel prize.
But basically, in the sludge of oceans in earliest earth, there were plenty of the building blocks of life. Lightning and radioactive decay of rock provided the energy and stirring to create relatively complex molecules.
IANAorganic chemist, but… Some of these grew to be RNA and then DNA that eventually got complex enough to catalyze reproductions of itself. Just like evolution for actual life, improved versions of these molecules push out the lesser ones. A virus is typically a string of DNA.
Eventually, some of these grow to include wrappers of protective molecular “skin”.
there’s no reason not to suppose that biochemical evolution is much different from biological evolution. The best results survive and thrive, because “survive” is how we define best. The complex fine-tuned single cells of today are far more complex than the originals,
Of course, when you’re talking about the origin of life, you also have a fuzzy-boundary problem. At some point in Earth’s history, you didn’t have anything at all remotely resembling life. At some later point, you started seeing increasingly complex interesting molecules, arranged in increasingly interesting ways. At some yet later point than that, you had things which were unambiguously alive. At what point do you cross the line from “interesting and complex arrangement of molecules that isn’t quite alive” to “life”? You can’t really pin it down.
And yes, it’s possible that life originated multiple times, and all but one line died out (presumably due to that one line eating all the others). The line that lasted and led to us might or might not have been the first to arise. In fact, I’ve seen arguments that suggest that life originated a few thousand times. If that’s the case, then the multiple origin events had to have happened in very rapid succession, because once a life form gets established, it wouldn’t take very long for it to spread across the world and adapt well enough that it could instantly outcompete any new upstarts.
The fact that you are repeatedly trying to get them to commit to your simple interpretation of a very complex issue makes me believe you are not asking it in good faith.
This is the part that may be impossible to ever prove. Life could have formed and been entirely wiped out at least once before we get back to the first living thing from which all existing life forms descended, and there may have been several early life forms that combined to become the most ancient ancestor. But there will still be the bottleneck somewhere more recent where one little critter was the ancestor of all things living now while all other forms of life at that time died off.
Or maybe not, we still don’t know of the existence of all livings things now. Maybe we’ll find a cell in some undersea volcanic vent which has ancestry preceding that bottleneck.
** Poo-Bah:** I am, in point of fact, a particularly haughty and exclusive person, of pre-Adamite ancestral descent. You will understand this when I tell you that I can trace my ancestry back to a protoplasmal primordial atomic globule. Consequently, my family pride is something inconceivable. I can’t help it. I was born sneering.
I suppose that even if there is a bottleneck like this, that the bottleneck could be something we don’t now consider alive, like a virus. I suspect this is unlikely, though.
IANAEVolutionary Biologist, but I think at a certain level of the evolutionary process you end up with a problem that genes are not always passed through procreation/mutation. At the size of really small multicellular critters, they can actually steal genetic material by consuming other really small multicellular critters. So that other really small multicellular critter isn’t a “ancestor” per say, but they are a part of the evolutionary tree.
Is there anybody who actually took a biology course or two that can explain it better. I’m basing this on a somewhat hazy memory of a YouTube educational video.
There is a lot of what is known as"horizontal" gene flowbetween microorganisms. That is, genes are transferred directly from one individual to another (rather than passed down from parent to offspring). This can happen even between very widely different organisms.
No, it has to be a self-replicator, which a virus is not. A virus depends on other things that are self-replicators, and evolutionarily, viruses must have arisen after self-replicating life was already well established (presumably by some sort of degenerative evolutionary process: something less complex developing from something more complex). Without self-replicators, the process of evolution by natural selection cannot get going. Before that, everything is just random mixing of chemicals, it is not life. There is no room for some intermediate virus-like stage. The problem of the origin of life is how a viable self-replicator managed to first emerge from random chemistry.