Godless Dave

A very good point. Even if you say "the odds are a billion to one..." it's no problem, as there are probably hundreds of billions of planets in the galaxy. But I think to even calculate the odds you would have to know more information than we presently have.

Oolon Colluphid

Sure. But guys, you’re missing the point. By your argument, we may as well say that eyes may form spontaneously in eyeless organisms, that feathered wings grew suddenly on the arms of an animal that didn’t have them... that the tornado whipped through the junkyard and did indeed assemble a 747, because there’s enough planets around for it to have not managed that on, and we’re just on the lucky 747-assembling one.

The point of cumulative selection is that you don’t need large chunks of luck, just lots of little bits, and only keeping the good results.

It may be that we are on the one ‘lucky’ planet where simple replicators spontaneously assembled. But everything after that is down to good old random mutation and natural selection.

So I object to my argument being called “needless”.

Oolon

Doubting Didymus

Oolon is right.

One thing that beausoleil and godlessdave are missing is that the kind of probabilities we are talking about here are astronomical. We don't know the exact figure, but the probability of a single cell forming from soup in a single step would easily outweigh the offset you would get from every planet in the universe, and probably a couple of times over. You are no longer looking at extremely improbable, you are staring impossibility in the face.

The first replicator (which I like to refer to as 'the abiogenesis thing'), would in fact need to be extremely simple, just to overcome the odds in the first place. No one can calculate for sure until we have a fairly good idea what the abiogenesis this really was, but it wasn't a cell and it wasn't a piece of DNA, they would be just too improbable for any sensible number of possible planets to overcome.

lpetrich

I had started a thread on <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=001624" target="_blank">Molecular Evolution before the Origin of Species</a>.

One lesson of evolution is that complicated structures often emerge in a piece-by-piece fashion, instead of all-at-once. And that lesson also applies to the earliest life on Earth.

That paper proposes that Earth life had gone through a precellular phase, the equivalent of a giant syncytial mass that had lived in the interstices of the mud and clay of oceanic hot springs.

Something like Ernst Haeckel's Urschleim and the famous misidentification that was Bathybius.

This simplifies the origin-of-life problem a bit, because in this picture, cells came after the first life.

Also in that paper:

Biological amino acids were acquired gradually, with more complicated ones being acquired after more simple ones. DNA is also a late invention, being a derivative of RNA.

And the metabolic enzyme ferredoxin is not only older than some cell-membrane-dependent proteins, it is adapted for sticking to a mineral surface in Wachterhauser fashion. Exactly what is needed for an Urschleim organism.

cricket

Doooon't stop.

Why?

Whatta you mean?

Sheep in the big city

Here is my take on the prebiotic soup:

God was just making soup again (very tasty with all the glutamate in it) and forgot about it over the weekend.
When he finally remembered there was already life growing on it, so he threw the biotic soup out in the garbage bin (our universe) in digust.

luvluv

I've heard there have been some difficulties in formulating one consistent theory for the origin of life. Is this true?

I also heard the panspermia argument had been refuted at the last ISSOL (sp?) conference, is that correct? It was stated that not enough pre-biotic materials could have made it to account for life on earth. (I'm paraphrasing horribly).

Also, are there any suggestions for the origin of DNA, specifically? Personally, this is where evolution and atheism make very little sense. DNA is a system of communicating and interpreting information, and only minds do that or formulate systems (like computers) which can do it on their own. IMHO.

MrDarwin

First, define "cell". Then define "life" and "alive". See the problem?

lpetrich

In a sense, yes. Despite ambitious efforts, this has proved to be a very difficult effort. However, there has been some impressive headway in two directions, forward and backward.

The forward approach is to see if one can get a living thing out of prebiotic chemistry. That goal has yet to be reached, though a variety of complicated molecules can be formed without much trouble. In particular, such biological building blocks as several amino acids and nucleic-acid bases can be formed without much trouble, though it is more difficult to produce ribose, part of RNA (very similar to DNA).

The backward approach is to extrapolate backwards from the properties of existing organisms using the techniques of evolutionary biology. One constructs an overall family tree of life and then works out what the tree's root must have been like. The outlines of that tree are now reasonably well-understood, though it has been obscured somewhat by lateral gene transfer and endosymbiosis.

The Last Universal Common Ancestor had had full-scale biosynthesis, metabolism that involved extracting energy from various chemical reactions, like combining hydrogen with sulfur, full-scale RNA-to-protein translation, DNA for master copies -- but a poorly-developed DNA-replication system.

This looks very disappointing, but one can look further by looking for evidence of gene duplications, vestigial features, and so forth. One interesting curiosity is that several metabolic coenzymes (some of the B vitamins) have bits of RNA in them, which is odd when one considers their function. To an experienced evolutionary biologist, this suggests "vestigial feature".

Which leads to one interesting reconstruction: the "RNA world", in which RNA molecules served as self-reproducing enzymes. However, these enzymes had a taste for using coenzyme molecules, and some of these were amino acids. This lead to the development of an amino-acid coenzyme assembler, which eventually became the RNA-to-protein translation apparatus that we find today. Eventually, the RNA dropped out of most of the enzymes, leaving the proteins to do most of the work. Another latecomer was DNA, which is simply modified RNA.

The RNA-world hypothesis leaves out the question of the origin of the RNA; as mentioned earlier, the origin of it its ribose building blocks continues to be a difficult problem.

However, some interesting work has been done on trying to date proteins by working out the amount of metabolism needed to produce their more-critical amino acids; a metabolic enzyme, ferredoxin, turns out to be older than some cell-membrane-dependent ones -- and turns out to be adapted for sticking to mineral surfaces.

So the first living thing on our planet may not have been compose of discrete cells, but may have been a continuous goo that lived in mud and clay and the like.

Panspermia is arrival of already-existing organisms. I'm not sure what you are referring to.

This claim is difficult to evaluate without some way of recognizing "information". Waves keep their shape as they travel; does that make them information carriers?

And the "mind" involved need not be the god of some religion -- it could be time travelers who have tried to insure that they will come into existence.

Psycho Economist

It's not "gaining scientific credibility" just yet... it's gaining popular recognition -- not the same thing. Astronomers are just itching to find enough evidence one way or another (and they may be pimping it to get more money), because it's a really interesting hypothesis... but it's still a largely untested hypothesis at this point.

I had a class with a guy who's on the Extra-Terrestrial Life existance committee of the International Astronomical Union, where I learned about Hoyle's neat supposition and where it stands in Astronomy.

[ November 05, 2002: Message edited by: Psycho Economist ]</p>