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Author Topic:   Some abiogenesis considerations
Annafan
Member (Idle past 2171 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 1 of 46 (335454)
07-26-2006 12:12 PM


Perhaps this has been discussed before, but anyways:

There is obviously a lot of speculation about abiogenesis. Particularly in the area of SETI, there is a lot of discussion about the likeliness of the development of life, what kind of life it would (have to) be etc. I'm sure opinions vary from life being extremely rare (or even just one, earth-based instance), and being exclusively carbon and DNA-based, to views that favour life as being almost an essential/inevitable product of the Universe under reasonable circumstances, and available in many chemical makeups and many hereditary/reproductive mechanisms.

In general, I have always held the view that both extremes could still well turn out to be true, because we simply lack substantial evidence or strong indications for either. (life on earth as one single datapoint, so to speak)

However, lately I'm starting to lean towards the "extremely rare" hypothesis, or alternatively the assumption that, even if life is abundant, it would still very likely be based on very similar chemistry (carbon and/or DNA or something very very similar). With a preference for the "extremely rare" hypothesis.

This is based on my very basic observation (which may well be wrong/uninformed) that ONE common ancestor for all currently existing lifeforms seems to be the prevailing idea in science at this point (?)

The (admittedly quick) conclusion that I draw from this, is that it is unlikely that development of life is BOTH almost inevitable, and at the same time shows a lot of tolerance when it comes to the exact chemical makeup. Because if this were true, many different types of life would be expected to originate in different places at roughly the same time, and/or different types of life would keep appearing throughout time. It looks like this is not the case, OR alternatively this may have happened (and IS happening at this moment?), but these "alternatives" turn out to have absolutely no chance in competition against "our" type of carbon/DNA based life. In which case they would appear in very limited areas, and disappear quickly again. But if we leave out the "many chemical makeups possible" idea, it still seems unlikely that one particular type (carbon/DNA) is highly likely to appear spontaneously. Because in that case, we would expect this event to have taken place in many different locations and timeframes, ending up with life that is chemically related/similar, but with many different first ancestors.

So, what I would like to see addressed here is, first of all, how strong the indications are that current life has indeed exactly ONE common ancestor. What reasoning/evidence is this idea based on (or ISN'T it the strong prevailing idea after all?) And are there escape routes for the "life is inevitable and can take on many forms" idea, given the possible counter-arguments I gave above? Any other related ideas are also welcome. :)


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AdminWounded
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Message 2 of 46 (335506)
07-26-2006 3:56 PM


Thread moved here from the Proposed New Topics forum.
Annafan
Member (Idle past 2171 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 3 of 46 (335679)
07-27-2006 9:07 AM


Abiogenesis is impossible
I need to choose my headers and subheaders more carefully, it seems. If they are not controversial enough, there doesn't seem to be too much interest...
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ramoss
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Posts: 3046
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Member Rating: 3.9


Message 4 of 46 (335739)
07-27-2006 12:58 PM
Reply to: Message 1 by Annafan
07-26-2006 12:12 PM


I think that one indication of the concept that there was a single ancestor of all living things is the percentage of genes that the various organisms have in common. Another is the morphology. While it does not discuss abiogenesis per say, it does say that there are indications that all current living things had a common ancestor.

Here is a web site that has a lot of information about the evidence for common decent.

http://www.talkorigins.org/faqs/comdesc/default.html


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Nighttrain
Member (Idle past 1586 days)
Posts: 1512
From: brisbane,australia
Joined: 06-08-2004


Message 5 of 46 (335953)
07-28-2006 5:36 AM
Reply to: Message 3 by Annafan
07-27-2006 9:07 AM


Re: Abiogenesis is imho-possible
I`m no biologist, AF, but the fact that bacteria have intruded into other species to a limited (but life-necessary) extent, seems to point to multiple lines of abiogenesis. I imagine in a time of non-bacterial dependence, other species may have managed on their own, but I can`t conceive how they coped.

Morphology seems to point to different origins, too, with a large number of species having mouth, eyes and other sense organs in close proximity and excretory organs at a distance. Versus others that have evolved along different lines.


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Wounded King
Member (Idle past 1687 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 6 of 46 (335957)
07-28-2006 6:07 AM
Reply to: Message 5 by Nighttrain
07-28-2006 5:36 AM


Re: Abiogenesis is imho-possible
I`m no biologist, AF, but the fact that bacteria have intruded into other species to a limited (but life-necessary) extent, seems to point to multiple lines of abiogenesis. I imagine in a time of non-bacterial dependence, other species may have managed on their own, but I can`t conceive how they coped.

Im not sure what this means and I'm certainly not sure how it has any relevance to the question of whether all life has a common origin. No species need ever have been bacterially independent since bacteria would already have been there extant in the environment. By the time any multicellular life reached a size suitable for bacterial colonisation I should think it would already to be host to innumerable bacteria.

I'm assuming you are thinking of things like gut bacteria rather than things like mitochondria or chloroplasts, but its hard to tell from your post.

Morphology seems to point to different origins, too, with a large number of species having mouth, eyes and other sense organs in close proximity and excretory organs at a distance. Versus others that have evolved along different lines.

I don't see how modern difference present much of a problem for common ancestry. if the different morphologies were the product of different abiogenetic events then how do you explain the sharing of a common genetic material and code? Not to mention the sharing of many of the same genes. Why is it not more likely that they have evolved along different lines having diverged from a common ancestor?

TTFN,

WK


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Annafan
Member (Idle past 2171 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 7 of 46 (336029)
07-28-2006 11:05 AM


in other words...
To prevent any misunderstanding: I certainly don't doubt (some form) of common descent. I don't think it's an anti-evolutionary thought in any form, either. I just wonder how certain it is, and which arguments support, that there was exactly ONE. Either ONE for absolutely all lifeforms that ever existed, or ONE for currently existing lifeforms. Where the former would of course be much harder to establish definitively.

For example, is this question an active field of research, or is it instead more or less assumed in the "background" and considered that research that focuses on other issues would also immediately reveal different 'first ancestors'?

Are there any 'lifeforms' that maybe (even just during a short period after their initial discovery?) fueled speculation that they could be an example of such 'alternative lineage'? I'm thinking about virusses, prions, the 'Mars bacteria'? It would be interesting to hear more about their position in this issue.

And to get back to another topic of my post: IF we find that current lifeforms have exactly ONE common ancestor, doesn't that strongly indicate that life started exactly ONCE in the past (on earth)? And that this indicates that it is unlikely that life is really "common" in the Universe and somewhat flexible when it comes to the chemical components and physical circumstances?

Now, there could be different interpretations of this... A first one, on one extreme, could be that life IS something we would call "extremely unlikely", and also (which maybe is another way of expressing it) very strict when it comes to the available building blocks and circumstances.

But of course it could also be that there ARE different alternatives, which appear quite regularly, but that natural selection quickly establishes our particular form of "life" as the absolutely dominant one. This would mean that, after a sufficiently long period of time, only Carbon/DNA based life would remain on any planet, even if it hosted other lifeforms before, or if other lifeforms continued to appear regularly throughout history AFTER the first carbon/DNA life first originated.

Hmmm.. I guess this is just my initial post somewhat reworded But it's the direction I would like this thread to take.


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Wounded King
Member (Idle past 1687 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 8 of 46 (336035)
07-28-2006 11:20 AM
Reply to: Message 7 by Annafan
07-28-2006 11:05 AM


Re: in other words...
I don't think the basic logic of the argument really holds up. why couldn't carbon based nucleic acids just have happened to be the first suitable form of 'living' material to arise and subsequently have had a sufficient temporal edge to be able to outcompete any alternative forms? Indeed subsequent activity of living organisms may have compromised an environment capable of giving rise to other systems.

Really this suffers from the same problem as any other about the speculative likelihood of abiogenesis, with only 1 actual sample and a wealth of possible variables we are severely handicapped in making any reliable measures of probability.

TTFN,

WK


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Annafan
Member (Idle past 2171 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 9 of 46 (336377)
07-29-2006 3:26 PM
Reply to: Message 8 by Wounded King
07-28-2006 11:20 AM


Re: in other words...
Wounded King writes:

I don't think the basic logic of the argument really holds up. why couldn't carbon based nucleic acids just have happened to be the first suitable form of 'living' material to arise and subsequently have had a sufficient temporal edge to be able to outcompete any alternative forms? Indeed subsequent activity of living organisms may have compromised an environment capable of giving rise to other systems.

Really this suffers from the same problem as any other about the speculative likelihood of abiogenesis, with only 1 actual sample and a wealth of possible variables we are severely handicapped in making any reliable measures of probability.

Of course very little can be said about it with any degree of certainty. Still, intuitively one would expect a very different situation from the current one if abiogenesis were reasonably flexible in terms of the possible chemical components and circumstances.

If we look at carbon/DNA life, we can see that it has conquered many, extremely different, environments. And within those environments, it has also split up into numerous ecological niches. Or in other words: there is plenty of opportunity for lifeforms to find a suitable place.

If abiogenesis was really flexible, I would expect this situation to also exist on a sort of 'meta' level. In other words: we would have a mixture of lifeforms of different chemical basis and possibly with different means of self-replication with modification, each positioning themselves in the environments and ecological niches that suite them best. Surely, some alternative forms would have certain advantages against carbon/DNA, if only in the most extreme circumstances?

I wonder whether this hypothesis has been investigated thoroughly already. I looked up 'extremophiles' in Wikipedia, but it didn't specifically address the genetics (I guess that means all known extremophiles are known to be included in our 'tree of life'...)

All this thinking has me really looking forward to the discovery of possible primitive life on Mars or Titan


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randman 
Suspended Member (Idle past 2491 days)
Posts: 6367
Joined: 05-26-2005


Message 10 of 46 (336423)
07-29-2006 6:25 PM
Reply to: Message 1 by Annafan
07-26-2006 12:12 PM


a quick comment
So, what I would like to see addressed here is, first of all, how strong the indications are that current life has indeed exactly ONE common ancestor.

Imo, if abiogenesis is real (highly doubtful from a science perspective imo), then we can say biology evolves from chemistry (so to speak), but if that is the case, then embedded within the rules of chemistry is the ability to evolve biological life forms. Simple enough, but let's take the next step in logic.

Then, we can say there is a commonality within chemistry that is what gives rise to life.

So the fact all or most life forms share similarities, such as DNA, is not necessarily due to originating from a single biological life form, but can be due to the simple fact of sharing common origins in chemistry. In other words, if chemistry is predisposed to give rise to biology, then there is no reason not to expect these principles to keep working, again and again, and the fact there are wide similarities within all species is not evidence at all for common descent.

Of course, the other commonality that can explain similarity is that there is a Creator (sort of like how one can spot a picasso as oppossed to a Renior).


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Annafan
Member (Idle past 2171 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 11 of 46 (336438)
07-29-2006 6:59 PM
Reply to: Message 10 by randman
07-29-2006 6:25 PM


Re: a quick comment
Thanks for posting in my thread. (I expected you when I started this, lol)

We'll have lots more responses now. :p

randman writes:

Imo, if abiogenesis is real (highly doubtful from a science perspective imo), then we can say biology evolves from chemistry (so to speak), but if that is the case, then embedded within the rules of chemistry is the ability to evolve biological life forms.

That sounds ok...

randman writes:

Simple enough, but let's take the next step in logic.

Then, we can say there is a commonality within chemistry that is what gives rise to life.

Fair enough...

randman writes:

So the fact all or most life forms share similarities, such as DNA, is not necessarily due to originating from a single biological life form, but can be due to the simple fact of sharing common origins in chemistry.

It could be, IF you conveniently disregard the multitude of indications that at least some of the similarities are highly unlikely to be of the 'functional' kind.

We all know the examples of the gene for vitamin C production and others.

And the fact that similar adaptation problems are tackled via many different routes (flight, eyes.. to name two). Which clearly indicates that there is a huge random component in the whole process. Which subsequently indicates that lifeforms descending from different 'first ancestors' would be extremely unlikely to share such similar DNA.

randman writes:


Of course, the other commonality that can explain similarity is that there is a Creator (sort of like how one can spot a picasso as oppossed to a Renior).

IF you disregard the many counter-indications... ;)

I'm not sure we'll be able to stay on-topic here :(


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RickJB
Member (Idle past 2583 days)
Posts: 917
From: London, UK
Joined: 04-14-2006


Message 12 of 46 (336449)
07-29-2006 7:26 PM
Reply to: Message 1 by Annafan
07-26-2006 12:12 PM


As others have pointed out, with a current sample of 1 there's little room for prediction. With regard to the chemistry, I have read that amino acids are by-product of the star cycle (along with other heavy elements and molecules) so, as I understand it (poorly), there MAY possibly be some basis on which to argue a common chemical foundation to all life....

It'd be interesting to hear from someone who's qualified in this field...


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randman 
Suspended Member (Idle past 2491 days)
Posts: 6367
Joined: 05-26-2005


Message 13 of 46 (336450)
07-29-2006 7:28 PM
Reply to: Message 11 by Annafan
07-29-2006 6:59 PM


Re: a quick comment
I think you aren't looking at the details enough. On another thread, anglehard posted the paper by Woese arguing for a progenote stating that is the only possible solution since the differences within the 3 primary kingdoms indicate the common ancestor to them could not have been simpler organization or some such.

Without getting too much into it, the fact is those differences don't fit well (and they are observed facts not speculation) with the idea of a common ancestor at all. They fit special creation and ID just fine, and can also fit the idea of multiple ancestors resulting from abiogenesis.

Of course, all of this leads to ID, not current mainstream evo models.


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randman 
Suspended Member (Idle past 2491 days)
Posts: 6367
Joined: 05-26-2005


Message 14 of 46 (336452)
07-29-2006 7:31 PM
Reply to: Message 11 by Annafan
07-29-2006 6:59 PM


Re: a quick comment
Also, note that evo claims of convergent evolution argue that different and similar forms arise via environmental pressures and so evos already refute ironically the claim that such similarities must be the result of a common ancestor.

Take DNA or actually any commonality. There is no reason at all to discount environmental aspects, is there, for these commonalities?


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RickJB
Member (Idle past 2583 days)
Posts: 917
From: London, UK
Joined: 04-14-2006


Message 15 of 46 (336457)
07-29-2006 7:37 PM
Reply to: Message 14 by randman
07-29-2006 7:31 PM


Re: a quick comment
randman writes:

Also, note that evo claims of convergent evolution argue that different and similar forms arise via environmental pressures and so evos already refute ironically the claim that such similarities must be the result of a common ancestor.

Wrong. If a homogenous form is able to spread over a wide enough area then vaying environmental pressures will come into play, most especially if sub-populations become isolated. There's no contradiction.

Edited by RickJB, : No reason given.


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