h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

There are two separate questions here - how did life originate, and why are we not still a big bowl of living soup?

I can't see how evolution addresses the first question at all. Evolution relies on reproduction, mutation and natural selection, all of which require life to exist in the first place. The first life must have arisen by other processes from non-living material.

Creationism doesn't really address the first question either - if we take God to be alive. Creationists could be more consistent with evidence by arguing "God created primordial soup" instead of "God created Adam", but they don't.

Another hypothesis: Life, in a steady-state universe - is eternal. It arrives on planets on meteorites in very simple forms, and evolves from there.

Maybe the theory that life arose by random interactions in a huge organic sea over billions of years is the best bet, but without knowing more (and I don't) it seems like avoiding an argument by throwing large numbers around.

I think the best answer I've seen to the "Why is there life?" question derives from the idea of paralell universes. If there is a paralell universe for every possibility, then it doesn't matter how improbable the spontaneous origen of life is. AS long as the probability is more than zero, there must be at least one paralell universe in which life spontaneously arose somewhere. No matter how rare such life-containing paralell universe are, and how rare life is in them, if life can only form spontaneously, we can be certain that we will be in one.

Intelligent observers can only be in paralell universes in which complex, self-sustaining systems arise.

Would you say that a consequence of this multiverse theory is that I will live for ever? (But you won't - or at least you will, but in different universes)

Given a dollop of anthropic reasoning, it seems that anything that might lead to my death, or even contribute to my aging is probable rather than certain, and as I can only observe my continued existence and not my death, I will therefore live for ever while everybody around my dies. Even the heat death of the universe is only a statistical prediction. Perhaps the big crunch is inescapable, and is there to save us from the torment of immortality.

I've heard tyhat argument made in a book by Martin Rees, a physisist or cosmologist who seems to know a lot about the subject and writes a lot of books for general consumption on physics and cosmology.

It sounds logical, but I don't konw enough to make a meaningful judgement about it. I wonder what RDO will say when he gets back.

The trouble with the multiverse hypothesis is that it is unscientific. There is no empirical test which can falsify it in the event that it is false.

This doesn't stop us using it in order to help us understand difficult ideas like probability or quantum physics, but we should remember that it is only a metaphysical gloss applied on top of more scientific ideas.

Life started 3.5 billion years ago, which is a quite a while after the Earth came about (4 - 4.5 bya).

The earth is Big and the ingredients for life Very Small, and there were presumably a lot of them all over the place. The odds of something self-replicating and simple appearing (say, some self-catalytic RNA - see rRNA) with those resources and at such timespans are not great at all. They require no parralel universes, no meteorites, and no Gods.

Given this, life may be pretty common in the universe. It's a wonderful thought isn't it?

Ste

PS I avoided big numbers pretty well there, don't you think?

You avoided big numbers by claiming they are small!

Sure you've the size of the ocean times billions of years times some plausible rate of reaction, divided by the "size" of the molecules concerned, times (if you allow weak anthropic reasoning) the number of similar planets in the universe.

The number you get out is really big and represents a LOT of random chemistry.

Multply this by a really small number representing the chance of a modest amount of random chemistry producing a minimal self-replicating system. And you will get something like a probability or frequency of life 'evolving' from scratch, unconditional on our existence.

I think the interesting question is how small is the really small number. This depends on how complex the minimal self-replicating system is. This in turn depends on the quality of raw materials. Your self-catalytic RNA would be OK if there was lots of nearly-"self-catalytic RNA" around, but this seems implausible. The trouble is that you need big complex molecules to catalyse simple little reactions, and a lot of simple little reactions (each requiring a different big complex molecule) to make one big complex molecule. Against this it could be argued that a catalyst can look for precursors in the whole primordial soup, and it is bound to find the right thing somewhere after a few million years if needs be. But it is also like to to find a similar reagent that will create the wrong product and break the chain.

So in short, it seems to me like a really really small number. Now this doesn't lead me to god because I am looking for explanations, and god would require more explanation than life. Unless you argue that eternal things need no explanation, but then I suggest that life could be eternal rather than god.

But hey, I'm not even throwing numbers around, I'm just talking about doing it. Also we should remember that we do exist, and so we should not feel daunted by tiny probabilities (if they turn out to be tiny). Unless there is a better theory, this tiny probability represents easily the most likely explanation.

'You avoided big numbers by claiming they are small!'

I avoided them in the same way that you avoided them: 'But hey, I'm not even throwing numbers around, I'm just talking about doing it.'


'The number you get out is really big and represents a LOT of random chemistry.'

Exactly. A LOT of chemistry. And it only needs ONE single event that spontaneously creates a self-replicator. So the odds that out of all this chemistry, after a billion years on an entire planet, something like RNA coming to be is not that great at all. It could even be something simpler than RNA, an evolutionary precursor that RNA developed from and outcompeted.


'I think the interesting question is how small is the really small number.'

Agreed

'This depends on how complex the minimal self-replicating system is.'

Let's again take RNA as an example.

'This in turn depends on the quality of raw materials.'

No it doesn't, if the raw materials are there, they're there. Quantity, perhaps.

'Your self-catalytic RNA would be OK if there was lots of nearly-"self-catalytic RNA" around, but this seems implausible.'

If something is self-catalysing it, by definition, doesn't need anything else, apart from substrates.

'The trouble is that you need big complex molecules to catalyse simple little reactions, and a lot of simple little reactions ... to make one big complex molecule.'

This may seem like a paradox, but we (obviously) know simple little reactions take place constantly, and we also know that these lead to more complex molecules such as amino acids and nucleotides. These polymerise to form proteins and nucleic acids. The 'big complex molecules' are not that complex.

'Against this it could be argued that a catalyst can look for precursors in the whole primordial soup, and it is bound to find the right thing somewhere after a few million years if needs be. But it is also like to to find a similar reagent that will create the wrong product and break the chain.'

If a successful self-catalysing system arose, it would likely be in a location where substrate was abundant, otherwise it wouldn't be successful (as life is).


'So in short, it seems to me like a really really small number.'

I disagree.


'Also we should remember that we do exist, and so we should not feel daunted by tiny probabilities'

But it is more likely, as we exist and by definition, that we came about because of larger probabilities, rather than tiny ones. Does that make sense? I hope so.




Ste

It sounds like your self-catalysing RNA catalyses multiple specific reactions which is quite remarkable for something simple. I usually think of RNA as a data structure rather than a "working" molecule, with other molecules or cellular structures doing the copying or protein manufacture. I would have thought that having the whole stuff of life in a single molecule would be so breathtakingly efficient that cellular life would never get a look in. I find the idea of a community of molecules replicating all the community molecules more plausible.

So how does this self-catalysing RNA work then? Why isn't it still around, and if it were, would it evolve into Grey Goo (TM)?



"But it is more likely, as we exist and by definition, that we came about because of larger probabilities, rather than tiny ones. Does that make sense? I hope so."

Should we let our existence warp our perspective on the problem? I think that in the context of a debate of the truth of the random chemistry theory of the origin of life, to assume the truth of the theory in order to argue for higher probabilities is to commit the crime of circular reasoning.

The actual math has been done on these probabilities, as early as the 1970's, possibly earlier. One of the situations required for life origins to make life as we know it is very similar to flipping a coin 237 times and getting all heads. Even with a 100 to 1 preference for getting heads if the last flip was a heads this is still highly improbable, and this was just one area.

Overall, the timespan of billions of years, and the amount of materials on Earth (indeed the amount of materials on all the planets in the universe, assuming a few hundred trillion solar systems) would not be enough to overcome the statistical problems of life origins using the current theory.

Clearly this information calls for a new theory, and it also calls for us to stop teaching the old theory as fact when it has been shown false.

Neil, the "actual math" depends very much on a particular model - a particular chemical pathway - for how life arose.


What particular theory do you say is being taught "as fact" and where?