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> But it sounds unlikely that a) there really was that single origin cell This is just a fact. All life that we know of has the same origin. Common descent is
by klmr 7y ago
> But it sounds unlikely that a) there really was that single origin cell
This is just a fact. All life that we know of has the same origin. Common descent is a core tenet, and one of the best established facts, of modern biology (https://doi.org/10.1038%2Fnature09014 https://doi.org/10.1038%2Fnature09014). For there to have been multiple distinct ancestors, we would need to see some relevant differences in the core machinery of life. And the fact is that, despite minor variations, we simply don’t see any. The odds of there being multiple distinct ancestors is astronomical, and would fundamentally impact our understanding of modern biology.
> and b) no organism has drifted in the millions of years of evolution
Organisms have drifted. That’s what evolution is. But evolution plays by rules, it can’t just change things willy-nilly. Changes to the core machinery would presumably either break it outright, or be so strongly detrimental as to be purified away almost immediately. Of course many genetic changes are deleterious to some extent but most effects can either be buffered for a short time because they are minor, or they confer some other advantage. In the core machinery of the cell this is much (!) less tolerated because even tiny chemical inefficiencies would immediately be amplified millionfold. Odds are, the DNA/RNA core machinery of all life sits in a steep local optimum. It’s not necessarily a global optimum but it’s essentially impossible to evolve out of because any individual change, or even a handful of coincidental changes, would leave the organism a lot worse off.
- naringas 7y ago> Common descent is a core tenet but that doesn't mean it's been proven through experimentation, does it? isn't it just an assumption? what if there's something akin to mathematical uniqueness in the mechanics of the core machinery? I mean it in the sense that it's either the way it is, or it's not really viable over a long enough period of time? such that it could have multiple origins which all nontheless converge into the same core mechanism?
- klmr 7y ago> but that doesn't mean it's been proven through experimentation, does it? isn't it just an assumption? It’s not an assumption, it’s backed up by excellent evidence — see the paper I linked. > what if there's something akin to mathematical uniqueness in the mechanics of the core machinery? Well that’s clearly not the case, we can trivially (…) design self-replicating machines that have completely different mechanics, as a thought experiment. More to the point, we can change parts of the machinery. For instance, we can take the universal genetic code and, with effort, change it into something completely different (by just swapping all codons around). The result is just as viable, but doesn’t exist in nature. In fact, the observed universality of the genetic code, in itself, is already seen as sufficient evidence for common descent (and then some).
- Terretta 7y ago> We can take the universal genetic code and with effort change it into something completely different ... just as viable, but doesn’t exist in nature. In fact, observed universality ... is sufficient evidence for common descent. Or, some would argue, evidence of a common designer.
- klmr 7y agoSome people argue that the moon is made of cheese. I don’t think that merits a mention either.
- Terretta 7y agoIt’s baffling to me these findings get closer and closer to software, some papers even use the term ‘design’, still other materials postulate our universe could be a simulation, and yet it’s mockable to consider whether there’s something cleverer than ourselves outside our universe that caused thus to be so. The question seems the same as, could an AI in a virtual world deduce or prove its artificialness or the reality outside the virtual? To me that’s more interesting than the simple credulity implied by moon cheese.
- jyounker 7y ago> Common descent is a core tenet... It's taken that (known) modern organisms descend from a common set of ancestors, but the tree of life isn't a tree. Organisms diverged and merged multiple times along the way to the modern world. It says nothing about how that/those points of common descent came to be. What originally constituted living things probably weren't very good at living by modern standards. They probably leaked like sieves, and they probably traded RNA, polypeptides, and other small molecules back and forth. When was this soup alive, and when wasn't it? I suspect it's just a continuum, and that complicated soup probably went back and forth across that grey zone of living-nonliving many times.
- klmr 7y ago> but the tree of life isn't a tree That’s correct but I don’t see what this has to do with my comment. It’s still a fact that all modern life, at some point, came through the same individual organism (EDIT: this should be population) which, furthermore, already possessed the fundamental machinery of DNA replication, RNA transcription and protein synthesis (amongst other things). EDIT: I misunderstood. Yes, you’re right: due to lateral gene/molecule transfer, it’s not certain that the last universal common ancestor was an individual cell, and at that time the label “individual” probably didn’t make much sense (although the paper I linked argues strongly that it was in fact one single cell).
- ejstronge 7y ago> That’s correct but I don’t see what this has to do with my comment. It’s still a fact that all modern life, at some point, came through the same individual organism which, furthermore, already possessed the fundamental machinery of DNA replication, RNA transcription and protein synthesis (amongst other things) This is a contentious statement that I don't think is established - a fact that the grandparent comment is trying to raise.
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