Doubting Didymus

I wouldn't say that. The fact that we are looking at something that was very very small and a very very very long time ago, it should not surprise us if we can not find fossils of the abiogenesis 'thing'.

What we DO have is a whole collection of working theories. With theories we can say things about probability. If you have a look at Morpho's alkaline seepage link, we can see a whole variety of testable aspects of the theory. Therefore we can test, observe, and match whatever data we can find to the competing abiogenesis theories.

If something is theoretically possible given a certain scenario, and we can test to see if that scenario is/was in place, then that should count as evidence that said something is both possible and likely.

So I wouldn't say that we simply 'don't know'. The prescence of multiple testable theories should blow the cover off of the old 'no evidence for abiogenesis' idea.

DNAunion

DNAunion: Took a look at one of the pages linked to earlier in this thread by A R Wallace.

<a href="http://www.postmodern.com/~jka/rnaworld/rna/base.html" target="_blank">http://www.postmodern.com/~jka/rnaworld/rna/base.html</a>

DNAunion: It’s not impressive at all (there are many better pages on the RNA World). For example, the page does not give any explanation for how the RNA World could have originated. About the closest thing is where they discuss directed evolution of a ribozyme that can bind nitrogen and carbon.

DNAunion: But adding those “right materials” invalidates the experiment as far as the origin of life or the origin of an RNA World goes. Since in the experiment (and in the prebiotic world) the ribozymes they used could not replicate themselves, RNA replication must have been performed (in the experiment) by adding large and complex proteins known are polymerases or replicases. Without these helpers there would have been no replication of the “better” RNAs, and therefore, no evolution. Without evolution, whatever the original molecules could do – which wasn’t that impressive - would be the same thing those molecules could do even billions of years later: they couldn't even do it better. How then do they lead to the origin of life, the origin of the RNA world, or the origin of self-replication? Those molecules would be useless, unless luck stepped in to accidentally form a first self-replicator – but that is what scientists are trying to get away from!

And to a lesser degree, we have to wonder about the selection of the "better" ribozymes. Sure, humans can select for whatever they want. But would nature have selected for RNA’s that could do no more than bind together one nitrogen atom and one carbon?

DNAunion

DNAunion: Looked at another of the links A R Wallace provided.

<a href="http://www.accessexcellence.org/WN/SUA03/RNA_origins_life.html" target="_blank">http://www.accessexcellence.org/WN/SUA03/RNA_origins_life.html</a>

DNAunion: Again, it does nothing to help explain the origin of life or the origin of the RNA World. (It discusses the same experiment as the previous link did).

Again, it used in vitro EVOLUTION to EVOLVE a ribozyme that was better at doing something that the original molecules were. EVOLUTION requires replication – something the “evolving” molecules themselves could not do.

The directed evolution did not lead to a self-replicating molecule – just something that could bind carbon and nitrogen together better after numerous rounds of selection and amplification. And even if it did EVOLVE a self-replicating molecule (which it didn’t), what would that demonstrate? That given self-replication self-replication can arise? That still wouldn’t address how self-replication originated.

The “only” thing in vitro (“test tube”) evolution experiments like this show is that RNA can perform more types of reactions than people originally thought. But even if one of these experiments ever does evolve a self-replicating RNA, it would not show HOW it could have happened in nature. It would only give us an idea of how small the fraction of self-replicating ribozymes is compared to the entire sequence space, letting us calculate a rough probability of how likely a self-replicating RNA would be to arise BY CHANCE ALONE.

[ September 24, 2002: Message edited by: DNAunion ]</p>

DNAunion

DNAunion: Looked at another one.

<a href="http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AbioticSynthesis.html" target="_blank">http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AbioticSynthesis.html</a>

DNAunion: I saw nothing of great importance there. If anyone else sees something at the page they think is worthy of discussion, feel free to copy it here.

PS: The Orgel page is the best of the lot so far. But it is also the longest. I am not going to go through it – if someone sees something there that he/she feels is impressive, then just post that paragraph here and I will try to address it (if I have time).

Same goes for the last link - it's needs to be narrowed down (show me the needle in the haystack).

[ September 24, 2002: Message edited by: DNAunion ]</p>

Starboy

Bravo, Vander. You make a good point. If one assumes that life can be spontaneously generated from natural causes, then why are we not seeing new life forms all the time?

Since as far as I know this doesn't happen then one might conclude that the original life-creating event was unique to a specific set of circumstances, which could be:

1). Your assertion: goddidit.
2). Science's assertion: It happened naturally.

Even if science never finds a conclusive explanation, godidit will not be accepted by science. I would hope by now that you could parrot back to me why that would be, even if you did not agree with it.

Starboy

DNAunion

DNAunion: Concerning the probability of a spontaneous origin of life: we may not know what it is, but we do have some sort of a vague upper boundary.

First, we have looked around at a great deal of our solar system and have so far found no other life. In addition, we have been scanning billions of frequencies for decades looking for messages from ETIs and have so far not detected any. If life were fairly likely to arise spontaneously, then we should expect to see life all over the place. But we don't. In fact, the only confirmed life we know of exists right here on Earth. The lack of detecting life "out there" (let alone a LOT of life "out there") implies that the probability of life's arising spontaneously is not that great.

Second, for more than 50 years scientists have been trying to create life from non-life in the lab and have failed. If the probability that life would arise spontaneously were actually high, then shouldn't have succeeded in our directed attempts by now? This too implies that the probability of life arising spontaneously is not that great.

In addition, IF life started with a self-replicating RNA molecule (as at least some theories suggest), then scientific experiments indicate that the probability of life arising by chance is extremely small as the closest thing to an RNA replicase evolved in a lab so far is nearly 200 ribonucleotides long -- and even this "best one" still can copy only 14 of those 200 (IIRC).

In other words, if you take a random lot of molecules, throw them into a "beaker" and impose random conditions (temperature, pressure, pH, etc.) on the system, the probability that life will originate in it are not very high. And in my opinion (and even in the opinion of at least some OOL researchers), that probability is close to 0.

[ September 24, 2002: Message edited by: DNAunion ]</p>

Doubting Didymus

I think most of Wallace's links are dealing with how more complex chemical reactions, protein sythesis, and thereby life, came from the original RNA world. I am not certain, but I think the problem is that you are looking for the 'first abiogenesis thing', when these links are really about how life as we know it came from the non-living world of RNA.

All the experiments you refer to, about RNA doing fairly mundane things like bind simple atoms are directed at establishing how the existing RNA world came to produce enzymes and proteins and whatnot.

This is 'abiogenesis' of a sort, because it is working on the processes that caused life to arise from replicating RNA (which is not 'alive'). It is not about the very first replicator (which would, obviously, have had to have happened by chance, as you say).

Doubting Didymus

Well, so what if the probability of spontaneous generation is very low? Given billions of years and god knows how many suitable planets in existence, the probability tat a very very improbable thing happening somewhere in the universe at least once could still be high.

This is Camaban's original point. We don't really know for sure how it happened, so it is not at all possible for us to assign any probability values.

DNAunion

DNAunion: But a self-replicating RNA would be alive: at least by OOL researchers' definition.

In (at least) undergraduate biology texts something is living if it is made of one or more functioning cells (the cell theory), or possesses all, nor nearly all, of the "universal" traits of organisms. An RNA replicase would not be living by either of these usages.

But in OOL circles, life is often defined as a self-sustaining, self-replicating molecule (or set of molecules). An RNA replicase would fit that definition. (In fact, the origin of self-replication and the origin of life are sometimes used interchangeably).

[ September 24, 2002: Message edited by: DNAunion ]</p>

DNAunion

DNAunion: Yes, this is what Dawkin's argues in "The Blind Watchmaker". But even he puts a lower limit on what we can accept for the probability, setting it at, I think, 1 in 10^20 (since he estimates there to be 10^20 planets in the Universe). That is the total amount of luck we are allowed to use in our theory for the origin of life (that is, if we also assume that the evolution of intelligent life such as humans is a given once life originates: if we think that somewhat improbable, we have to borrow some luck from the origin of life to account for our own evolution).

Going back to assumption that life originated as a self-replicating RNA molecule, it might be that the probability is smaller than 10^-20. In fact, Orgel calculate that it would take 10^40 UNIQUE RNA sequences to chance upon RNA replicases to kickstart life, and that estimate was based on a mere 40-mer. As I stated above in this thread, the closest thing so far -- which is still along way away from an RNA replicase -- is nearly a 200-mer, and the paper said it would probably have to be longer to be truly functional. If we assume it must be 200 monomers in length, then the probability of hitting upon such a sequence by pure chance drops immensely.

I think this kind of reasoning is why at least some scientists consider the orign of life to be a probabilistic fluke and too improbable to have happened twice (kind of life flipping a coin 500 times and getting a certain sequence; it can happen once, but won't twice). And as such, it is not the province of science (you really can't give a scientific explanation for a one-time immense stroke of luck - it just happened).

[ September 24, 2002: Message edited by: DNAunion ]</p>