On the hunt for aliens...*UPDATED* Amazing news!!!

By joining our community you will have the ability to post topics and access other forums reserved for members. Registration is quick, simple and absolutely free. Join our community today by clicking here.

Posted: Thu May 24, 2007 8:00 pm

Gnasher wrote:

if they are capable of travelling across the universe to find us, why can they only find out about our species by abducting a few rednecks and shoving a probe up their arses?

Perhaps they just have a sense of humour. Seriously though, if the universe is infinite, then the possibilities are also infinite. There will be an infinite number of planets like ours where there's an internet with a forum called '419eater', and an infinite number of near-matches, too. Get yer head around that. Neutral

Posted: Thu May 24, 2007 11:24 pm

phoglady09 wrote:

Ah, amino acids! finally something I can understand...<Snip>... My prof had a great research paper copied off for all of us, I'll have to see if I can dig it up somewhere. It was written by a group of scientists who set up an experiment to see if they could create life; they tried to replicate everything as best as they possible could, regulating the temperature, maintaining moisture, etc. etc. After a while they found that they had indeed created amino acids! ...

The Urey-Miller experiment.

One problem was that Nature ran the experiment for considerably longer than any researcher could ever do. Advent of the replicating molecule and development of the cell membrane are also considered pivotal in the development of more complex life. That's why so much attention is focussed on Mars as there may be evidence of early life there. Whether Mars has extant life is moot.

Posted: Thu May 24, 2007 11:57 pm

Thanks

It was starting to bug me that I couldn't remember much more about it...and the giant pile of old papers in the bottom of my closet probably wasn't going to produce anything useful...
*bows out of the conversation to allow smarter people to talk*

Posted: Fri May 25, 2007 12:51 am

I found it. This is from a great book by Bill Bryson called �A Short History of Nearly Everything�. If you are interested in this kind of stuff, but don�t have a calculator, I highly recommend it.

This is from a chapter where he talks about how amino acids assemble themselves into complex proteins that are fundamentally critical to all known life on earth:

Quote:

...<snip intro> The problem is that words in the amino acid alphabet are often exceedingly long. To spell collagen, the name of a common type of protein, you need to arrange eight letters in the right order. But to make collagen, you need to arrange 1,055 amino acids in precisely the right sequence. But- and here�s an obvious but crucial point- you don�t make it. It makes itself, spontaneously, without direction, and this is where the unlikelihoods come in.

The chances of a 1,055-sequence molecule like collagen spontaneously self-assembling are, frankly, nil. It just isn�t going to happen. To grasp what a long shot its existence is, visualize a standard Las Vegas slot machine but broadened greatly- to about ninety feet, to be precise- to accommodate 1,055 spinning wheels instead of the usual three or four, and with twenty symbols on each wheel (one for each amino acid). How long would you have to pull the handle before all 1,055 symbols came up in the right order? Effectively forever. Even if you reduced the number of spinning wheels to two hundred, which is actually a more typical number of amino acids for a protein, the odds against all two hundred coming up in a prescribed sequence are 1 in 10^260 (that is a 1 followed by 260 zeros). That in itself is a larger number than all of the atoms in the universe.

<snip some background> A protein to be of use must not only assemble amino acids in the right sequence, but then must engage in a kind of chemical origami and fold itself into a very specific shape. Even having achieved this structural complexity, a protein is no good to you if it can�t reproduce itself and proteins can�t. For this you need DNA. DNA is a whiz at replicating- it can make a copy of itself in seconds- but it can do virtually nothing else. So we have a paradoxical situation. Proteins can�t exist without DNA, and DNA has no purpose without proteins. Are we to assume then that they arose simultaneously with the purpose of supporting each other? If so: wow.

He goes on to talk about how it can be considerably simpler, but in all practicality, the odds don�t improve much.

In short; life, based on our understanding of it, is impossible.

Forever n00b Joined: 11 Jan 2006 Posts: 432

Not to hijack the thread, but I'm at a loss as to how the flagellum motor evolved. This is basically a bacterial propulsion system consisting of a motor, shaft, and propeller, each of which is useless without the other two. So did the whole thing randomly assemble, or how would something like this come to evolve, since each part in and of itself would not be of benefit without the others? I was just thinking . . . Wink

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

Everything looks a long way away when you're looking down the wrong end of the telescope. In a long thread of causes and effects, you are both arguing from the last effect to the first cause, when you should be arguing from the first cause to the first effect.

Evolution did not think, "hey I need Collagen, now how do I go about making that?" It picked up a random molecule and said "hey, that has a useful effect; I'll use that." In order to prove that collagen is so unlikely, you first have to prove that absolutely no other protein (or group of them) would have had a better survival value at the time it was first used. Since then it has been available in the toolkit. Of course life depends on it, but now that life has collagen there is no unlikelyhood in it being invaluable.

DNA primarily self-reproduces. A self-replicating molecule is going to have a massive evolutionary advantage over molecules that rely on random events to get created. The question is, how simple can a self-replicating molecule be? The primordial soup was thick with amino acids and other random organic molecules, so the first self replicator could depend on there being some common stuff to hand.

Regarding the flagellum, I think it is important to remember that mutations that do not decrease survival rates, do not get selected out. A mutation does not have to be a benefit to be propagated, just not a liability. Also part of that system may have mutated from something that had an entirely different function.

The flagellum is an interesting feature because it is so unlikely. However it seems to me that it only evolved once, and its existence isn't necessary for any higher life-forms to exist. If it had not evolved then we would not miss it. There are many such systems that could have evolved but didn't. If flagella had not evolved but lasers had, then we would be equally astounded by the lasers.

Posted: Fri May 25, 2007 1:39 pm

Yes, except that the primary role of DNA is not self-replication. In addition to self-replication it also functions as a template for RNA synthesis. Which of these processes occur is controlled by factors such as the availability of precursors, the abundance of substrate and the types of enzymes involved. DNA itself has no immediate use for amino acids. It replicates itself using nucleic acids, an entirely different class of biomolecules. RNA (single strand nucleic acids) is the molecule that encodes proteins using available amino acids. And no molecule is entirely self-replicating. DNA synthesis relies on an enzyme complex (DNA polymerase) to unwind and separate the double helix, then attach the correct sequence of nucleic acids to the separated strands. RNA synthesis, a precursor to protein synthesis, follows a different pathway involving different enzymes [and different substrates for that matter].

Anyway, as interesting or not as all this might seem, it�s similar in some ways to the example of the flagellum. DNA in isolation, despite its molecular complexity, cannot really do anything, and has no real advantage over other molecules. The other molecules such as the RNA, and structural and functional proteins, had to co-evolve, or at least co-exist, for anything significant to happen. It�s like the old question of which came first. You seemingly can�t have an enzyme without the DNA to synthesise the RNA that encodes the protein, but at the same time DNA and RNA can�t do anything without the enzymes that catalyse their synthesis and the amino acids that provide the substrates for protein synthesis. Hence the �primordial soup� theory I suspect. You had to at least have all that junk in the mix for anything to happen. But it�s still a quantum leap from a stew containing all the right components, to even the most primitive life form.

My personal opinion, for what it's worth, is that our chances of finding life anywhere else are approximately zero. And that discussion of the existence of life elsewhere, is strictly speculation. Very convincing at times, but still speculation. Hell, we can�t even adequately explain our own existence. There�s nothing wrong with speculation, of course. That�s human nature. It�s always been human nature to try and explain the inexplicable.

Posted: Fri May 25, 2007 1:41 pm

Quote:

...In a long thread of causes and effects, you are both arguing from the last effect to the first cause, when you should be arguing from the first cause to the first effect.

Excellent point. Like when I look up on a beautiful day to see the blossoms on the trees, and get hit in the eye with bird shit. When I think of the chain of events that had to occur to allow that bird shit to hit my eye in that exact moment in time, I can only conclude:

A- The odds against it are incalculable, therefore my understanding of it is flawed.
B- It could only have been preordained.
or
C- It happened that way because that's the way it happened.

Still it becomes important for the question about life in other places. We assume that there is life elsewhere because there is life here. But if life arose on earth because of some incredibly unlikely event, that dramatically drops the chances of it happening elsewhere. If, however, life arose on earth from ubiquitous ingredients and conditions, or if the required seminal innovations happened beyond the confines of earth, then the universe is teaming with life.

Posted: Fri May 25, 2007 3:30 pm

or D: The bird just had a spicy curry dish for breakfast

Posted: Fri May 25, 2007 3:38 pm

^^Yes, but what are the odds of that?

Forever n00b Joined: 11 Jan 2006 Posts: 432

thud419 wrote:

In a long thread of causes and effects, you are both arguing from the last effect to the first cause, when you should be arguing from the first cause to the first effect.

Can you explain this a bit further? When all that is available for our observation is the last effect, how else do we speculate upon how the effect came to be without looking backwards? When I'm reconstructing an accident scene, I have to look at what is there, the end result, and walk through it backwards to arrive at the original cause. It would be nice if I were there at the beginning and watched the whole thing unravel, but alas I'm forced to try to piece together what occurred after the fact, using only the evidence at hand. Am I totally missing your point here?

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

The best way to handle it would indeed be to work from the last effect back to the last cause and so on back to the beginning. But evolution cleans up after itself; there is no intermediate evidence to analyse. Worse still, we do not understand enough of the intervening processes in order to trace our way backward.

It is like trying to analyse that accident scene with no grasp of physics, no idea what a vehicle looked like before it crashed nor any understanding of why it might have been on the road in the first place or what it was doing. In analysing the car crash that is life, we have come to some understanding of the tensile strength of steel and are well on the way to producing a full road plan as it was after the accident. That still leaves a lot of work to do, and we have to learn how to do that work before we can do it.

In determining just how unlikely DNA is to have evolved, we should not assume that it arose fully formed out of a random soup of organics. It does not need to have done so. All that needs to have happened is for one of those molecules to have had the ability to build copies of itself.

One way it could have gone forward from there is that random mutations over time would have created an ecosystem of molocules, some of which self-replicated, and some of which were parasitic on the self-replicators. One of the parasites may have been proto-DNA.

That proto-DNA then became the centre of another ecosystem that out competed and replaced the first. One strand of DNA can encode not just its own replicator, but also other helpful and not so helpful substances.

In this molecule-eat-molecule world there would have been a clear advantage in building a cell wall that enclosed a subset of the entire ecology that was self-sustaining. It is this subset, not just the DNA, that is our ancestor.

In our own evolution this may have happened twice: Once for the nucleus, which is an incomplete ecosystem, and once for the cell. Or it may have been the other way round, the nucleus wall providing a extra line of defence against invaders.

These proto-cells would then have formed their own ecosystem and have been strengthened by many waves of evolution until they achieved some similarity to the cells that we see today.

Whatever happened it is important to remember that every lifeform on the planet has been evolving for the same length of time. We did not evolve from chimps; chimps have been evolving for just as long as we have. We both evolved from some proto-ape that no longer exists. In the same way, cells and the molecules that make them have been evolving for much longer. There is no reason to think that the first cells were the same as the bacteria that we study today, or that the modalities of the first self-replicating molecules bore any resemblence to the complex life-cycle of DNA.

Forever n00b Joined: 11 Jan 2006 Posts: 432

thud419 wrote:

The best way to handle it would indeed be to work from the last effect back to the last cause and so on back to the beginning. But evolution cleans up after itself; there is no intermediate evidence to analyse. Worse still, we do not understand enough of the intervening processes in order to trace our way backward.

It is like trying to analyse that accident scene with no grasp of physics, no idea what a vehicle looked like before it crashed nor any understanding of why it might have been on the road in the first place or what it was doing.

That being said, would you have any confidence whatsoever in a theory posited by such an accident reconstructionist as to the cause of said accident?

On another note, evolution assumes gradual change over millions of years, with previously existing species transforming into new ones, correct? If this is the case, wouldn't it be safe to assume that a number of intermediary species must have lived and left behind fossils? I would suspect that the number of fossils of intermediary species would be massive. Has our searching over the last century and a half produced any half fish/half reptile fossils? Have we uncovered the fossils of any transitional species at all? Or does the fossil record lean more toward a sudden and fully formed appearance of life?

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

Edit: In answer to your first point, I see your point. That depends on the basis of the theory. I happen to think the proposed theory is more likely than the opposed theory based on my understanding of their derivation.

Bustyn_Yuhrass wrote:

Evolution assumes gradual change over millions of years,

Likely not. It is more likely that a species is stable while its environment is stable. Only when its environment becomes unstable or other external forces come into play does an evolutionary force exist. This force is likely to produce a large number of changes relatively quickly in relation to the lengths of time the enviroment is stable.

Quote:

...with previously existing species transforming into new ones, correct?

No. Evolution assumes the emergence of mutations into seperate species living alongside their root stock. While is is generally accepted that the root stock eventually becomes extinct due to out-competition this is not necessarily the case where, for example, the new mutation fills a different environmental niche.

Quote:

If this is the case, wouldn't it be safe to assume that a number of intermediary species must have lived and left behind fossils?

Yes. However the fossile record depends on creatures having left fossiles and us finding them. Fossilisation is a rare event, requiring unusual circumstances. Similarly it requires unusual circumstances to bring those fossiles where we can see them. It is incredibly rare for the circumstances to be so benificent that we find fossiles showing fine or soft structures. Since any life much further back than the first dinosaurs had a soft skeleton, and the first single celled organisms were very small it is not surprising that we don't find many fossiles from those epochs.

Quote:

I would suspect that the number of fossils of intermediary species would be massive. Has our searching over the last century and a half produced any half fish/half reptile fossils?

Yes. See the following:
http://en.wikipedia.org/wiki/Lobe-finned_fish
http://en.wikipedia.org/wiki/Acanthostega
http://en.wikipedia.org/wiki/Eryops

Quote:

Have we uncovered the fossils of any transitional species at all?

Yes. See http://en.wikipedia.org/wiki/List_of_human_fossils

Quote:

Or does the fossil record lean more toward a sudden and fully formed appearance of life?

No, not at all. Our abilities and the fossile record are against us seeing any further back than simple single-celled organisms, and we have found those. See http://en.wikipedia.org/wiki/Archean#Archean_life and http://en.wikipedia.org/wiki/Prokaryota

Posted: Sat May 26, 2007 7:11 am

I thought I'd try to clarify a few things and expand a little too. Hopefully it's not too technical.

DNA is a rather complex (information storage) molecule governing development and function of the whole organism. RNA is a chemical messenger which transfers protein synthesis information from DNA to ribosomes. Both would seem to be far too complex to have developed early in the evolution of simple life. Rather than considering early molecular evolutionary success as through better competition, it might be better to look at the problem in terms of rates of chemical reaction. The higher the rate of reaction, the greater the output.

All chemical reactions require a certain amount of energy (Activation Energy) to start, and once it begins, the reaction proceeds at a rate according to reaction kinetics. A fundamental barrier to a chemical reaction starting is indeed the amount of energy required to start it. As alluded to in the Urey-Miller experiment, thermal and electromagnetic (particularly U.V.light) energy from both the Earth and sun may well have provided sufficient activation energy to start some simple reactions in the first 500 or so million years since planetary accretion. Later, as the earth cooled is when catalysts probably became more significant in molecular evolution.

Initially, the catalysts might have been fairly simple chemicals such as dissolved minerals in water or those present in early rock masses. As time progressed and the Earth cooled, it is probable the random reactions between simple organic compounds and other minerals resulted in the formation of numerous novel compounds, most of which were likely only spectator compounds or were consumed by other reactions. Fewer may have been active as catalysts. It follows that any catalyst or catalyst like compounds that increased the productivity of a few sets of chemical reactions would be pivotal, particularly if the resultant products or by-products incorporated some form of catalyst. It may be the same reaction or other reactions that benefited. This creates a positive feedback loop and would result in a significantly amplified output if the reagents are plentiful.

In turn, molecular diversity probably would also increase.

Interestingly, the catalyst as a self perpetuating reaction product could well be the origin of the first molecular memory ("genetic code") or organic information storage system. Whether the RNA World Hypothesis is valid remains moot but it is possible that simple Amino Acids then A.A. based short polymers acted as the first organic "catalytic codes".

There are others who opine the more robust Peptide Nucleic Acids (PNA) were the original code. Similarly, others propose Threol Nucleic Acid or Glycol Nucleic Acid. Yet another interesting idea is that Polycyclic Aromatic Hydrocarbons (PAH World Hypothesis) played a significant role. The step to more robust DNA and protein synthesis probably took considerably longer. I suspect some or all of the these processes were significant.

The cell membrane and cell wall were later additions and their origins still remain the subject of debate. In primitive cellular life, the membrane would have acted as a simple semi-permeable barrier to the external environment which buffered the internal environment and prevented ingress of unwanted molecules (poisons or reaction inhibitors). Reagents (nutrients) could diffuse into the cell and waste products could diffuse out (along their respective concentration gradients). More advanced control of the internal environment was likely a later addition and would have been an evolutionary advantage in more advanced cells. Replicated Organic Catalysts probably just accumulated to form an early Syncytium (multinucleate cell).

As for the cellular complexity of higher organisms, there is a theory, the Endosymbiont Hypothesis which still remains the most popular explanation for organelle origins in Eukaryota. The mitochondria are an interesting organelle as the inner membrane is compositionally similar to that of the Prokaryota Ref. whilst the outer membrane composition resembles that of Eukarote plasma or cell membrane Ref. Interestingly, Mitochondria have their own independent genomes as do Chloroplasts Ref. It is considered mitochondria and choloroplasts are internalised (assimilated) prokaryotes and the remaining genome is essential for the organelle's function.

For a complex chemical soup to give rise to simple self replicating molecules and then simple life entails a there being a fairly specific set of initial conditions and a long (500 million to 1.5 billion year) wait for the random processes to produce the right outputs to feed the next evolutionary stages. Multicellular life is the next rung on the evolutionary ladder. I'll stop right here.

Is or was there life elsewhere in the Universe? Probably. Sentient life? Less probable. Intelligent life? Technologically advanced life? The probability falls even further but the chance of finding it or it finding us still remains marginally better than Nil.

So, what do we look for in the search for evidence of life elsewhere? Assuming the Earth as model system for the evolution of life, then Earth like planets and Sol like stars would seem to be a good start. Hence the interest in Mars and the huge capital required for that kind of endeavour.

As with many other research disciplines, a lack of funding and participants hampers progress in this fascinating research field.

Baiting Guru Joined: 04 Jan 2006 Posts: 3193

Fascinating, thanks.

Posted: Sun May 27, 2007 4:28 am

Superb. Thanks to all for making this thread such a worthwhile read

On the hunt for aliens...UPDATED Amazing news!!!	View next topic View previous topic