No slave race: no evolution

[eMesreveR]

Just saying right now, "life" did not have to start with nucleotides. You don't need DNA to make life. We need DNA for life as we know it, but all we really need is something that self-replicates and is capable of mutation. Then natural selection works its charm and voila! diversity!

 

[Chalnoth]

Just saying right now, "life" did not have to start with nucleotides. You don't need DNA to make life. We need DNA for life as we know it, but all we really need is something that self-replicates and is capable of mutation. Then natural selection works its charm and voila! diversity!

Well, while it is potentially possible that some other sort of life might be able to form without the nucleotides which we know and love, our life almost certainly started with nucleotides.

 

[Chalnoth]

Great, now how many nucleotides in the minimum viable life form?

Er, that's all of them that are found in both DNA and RNA:
adenine, cytosine, guanine, thymine, and uracil

There aren't any more that are commonly used by life.

 

[EnemyPartyII]

Well, while it is potentially possible that some other sort of life might be able to form without the nucleotides which we know and love, our life almost certainly started with nucleotides.

Um... not necesarily... early self reproducing molecules were probably like prions... and nucleotide based information was a later adaptation

 

[Chalnoth]

Um... not necesarily... early self reproducing molecules were probably like prions... and nucleotide based information was a later adaptation

Well, I believe the prevailing hypothesis at the moment is that the first self-replicators were RNA-based, and DNA and proteins only came later, for the reason that RNA can act both as information-encoder and as a catalyst for chemical reactions. The problem with proteins as the first self replicators, from what I understand, is that it's much more difficult for them to act as information carriers.

 

[EnemyPartyII]

Well, I believe the prevailing hypothesis at the moment is that the first self-replicators were RNA-based, and DNA and proteins only came later, for the reason that RNA can act both as information-encoder and as a catalyst for chemical reactions. The problem with proteins as the first self replicators, from what I understand, is that it's much more difficult for them to act as information carriers.

I'll see your RNA hypothesis and raise you a black smoker crystaline surface prion formation hypothesis

 

[Chalnoth]

I'll see your RNA hypothesis and raise you a black smoker crystaline surface prion formation hypothesis

Well, I'll let the abiogenesis people work it out, but either way, the base chemicals that make up life (whether nucleotides or amino acids) aren't hard to form in natural conditions without life.

 

[EnemyPartyII]

Well, I'll let the abiogenesis people work it out, but either way, the base chemicals that make up life (whether nucleotides or amino acids) aren't hard to form in natural conditions without life.

Oh, indeed. Miller Urey et al...

 

[ChordatesLegacy]

What's more, if we did learn enough to nail this down, I don't think it would be simply quoted as a probability of abiogenesis happening at all. It would instead be a probability per unit time, or conversely an average amount of time it takes (given many planets with the same conditions) for life to arise.

Absolutely; unit time would most certainly be a parameter of any probability of abigenesis occurring. But at present the statistical analysis is impossible, just too many unknowns.

 

[tanzanos]

Here's the basic problem with human evolution. Start with the proposition that the human brain provides a competitive advantage over monkey brains. Then accept the proposition that Neanderthal brains and other transitional brains would have provided competitive advantages over monkey brains (otherwise, no natural selection). Then accept the proposition that homo sapiens brains provide a competitive advantage over hypothetical Neanderthal brains. Now, monkeys are still around, and as a family, monkeys have survived rather well.

Just goes to show how one gives an explanation on a subject he knows very little about. If you have a child born with six fingers does that mean that all your other 5 fingered children will cease to exist? Evolution creates diversity and whether any part of that diversity will or will not survive depends on whether it is suitable to survive in its given environment. Eventually all life has a common ancestor. All apes and monkeys have a common ancestor. All life mutates (even humans; look at how many six fingered and other deformities exist) and that is exactly what makes something evolve. If that mutation is able to exist and pass it's genes then it will not become extinct. We can see this in dogs. Some dogs have been selectively bred (human induced evolution) to be better suited to certain areas of human needs. Were evolution not possible then breeding would not be possible.

Actually humans evolved larger brains because a mutation that caused smaller weaker jaw muscles allowed for cranial expansion thus allowing for a bigger brain amongst other things. It would takes volumes to explain evolution and is impossible to do it in a post; so creationists will do well to pay a visit to their local library!

 

[Vene]

Um... not necesarily... early self reproducing molecules were probably like prions... and nucleotide based information was a later adaptation

The problem with that is prions 'reproduce' by taking existing proteins (or newly formed proteins) and denaturing them into prions. Without genes I have a hard time seeing how they could have evolved (I know, argument from incredulity). That's why I like the RNA world hypothesis, RNA can replicate without the aid of proteins, there is an existing cell membrane, and even a very basic metabolism. It also allows for evolution due to early 'life' containing genes. But if somebody shows that a cell-like structure can from from prion-like molecules, great, I'll change my mind. None of this stuff is as strong as we'd like.

 

[Naraoia]

Great, now how many nucleotides in the minimum viable life form?

Depends on what you mean by "life form", I guess.

IIRC the TalkOrigins essay (yes, the one I keep trying to get you to address) mentions a self-replicating hexanucleotide (I also dimly recall that it was all Gs and Cs but I can't be bothered to look that up now). If life form = replicator then the minimum is less than or equal to six.

Now whether a hexanucleotide is enough to evolve a bigger genome, I have no idea. My... semi-WAG is that you need something bigger than that, with an actual catalytic site*, because if you start adding nucleotides to a simple RNA sequence, sooner or later it will end up in a tangled mass, base-paired with itself in all sorts of places, which prevents it from being a template unless it's unravelled somehow. (Although sometimes RNA does remain nicely untangled, so maybe all RNA sequences can copy themselves at a low rate? Gosh, I know so little about RNA )

*I don't recall that the hexanucleotide was a catalyst as well as a template, but of course that may be my patchy memory. I only skimmed part of the relevant paper, and that long ago.

 

[True_Blue]

This is a good discussion, you guys.