Well this site is about Life, the Universe and Everything, so where better to bring this up?
I am just starting to read Carl Sagan’s “The varieties of scientific experience” and just in the first few pages it had me revisiting this old problem of mine.
Life as we know it, in all its forms is based on DNA – on this planet at least. Life as we see it all around us has been undergoing evolution ever since it kicked off – I’m very happy with that. What I was (and still am) very unhappy about is the apparent lack of DNA precursors. DNA is a pretty complex molecule, are we meant to believe it just suddenly arrived, completely built and ready to go? There is an analogy often made about this regarding a hurricane going through a metal scrap yard and creating a pocket watch – but the probabilities of course are much lower than this. So, my initial naive way of thinking went like this, there must have been simpler DNA precursors which themselves underwent evolution to give us the DNA we see today. Problem is, we don’t see any evidence of these precursors and we don’t see any life on this planet based on anything other than DNA. I actually knew the answer to this one but still came up with the stupid idea anyway. What is the answer? The answer is, it’s DNA all the way back, right back to the beginning – the first forms of life on Earth were based on the same DNA structure, so there were no precursors, like turtles, it’s DNA all the way down.
Now I really do have a problem, but I also have a solution to the Fermi problem. My problem is this. What is the likelihood/probability of the DNA molecule coming together like that something like 4 billion years ago? The observer’s answer is that is must be finite ‘cos here we are. Finite yes, but how small a finite are we talking here? 10^-20? 10^-100? 10^ -Googol??
I have been heard to say on television (Chris Packham’s Inside Out BBC programme) that there is “life out there” – that the Universe is teeming with life. I would like to change that one slightly in the view of this DNA business. I don’t think there’s any life out there beyond this planet, none at all. Nothing based on elements other than Carbon or molecules other than DNA – nothing. There’s your answer to the Fermi problem. We haven’t heard from them yet because there’s nobody out there calling.
This does create a rather important corollary. We should be just a little more considerate and caring not only of each other, but all the creatures on this planet – and of course the planet itself. Stupid boys with idiot haircuts spouting nonsense intended to upset the other people on this planet are not helping things along much. It really is time to grow up – fast.
There is very little evidence of any soft tissue evolution in the fossil record. It is only recently that we find that dinosaurs might have had feathers. I suspect that fossil early kidneys are absent. This would indicate that fossil molecules are almost impossible to find. So early forms of DNA might have existed but the details are unobtainable.
I guess I didn’t write too clearly in the original post. Since DNA as we know it today was also there right back at the beginning (I am thinking of Stromatolites still found in Shark Bay Australia) it means that the current version of the “molecule of life” was there, complete, right from the very beginning. Given that, it doesn’t really matter if there were other non-DNA life-molecules floating around that haven’t made it to the present day – we really do have the hurricane in a scrap metal yard making a pocket watch scenario on our hands.
I can’t see DNA simply springing into existence without precursors.
I like the Archway Analogy. A self-supporting archway doesn’t just spring into existence – it relies on scaffolding for it to be built upon. Scaffolding which is removed when no longer required. In the finished article there is no physical evidence of the scaffold.
It could be argued that the lack of evidence for early lifeforms running on DNA precursors implies that this development phase passes very quickly. The evolution of DNA-like molecules is in fact highly likely and is reached very quickly once the early precursors get started.
I do think the “early precursors” are still pretty hard to come by 🙂
The current consensus by experts in the field (I questioned them at Starmus) was that there were no precursors. With no evidence to the contrary I reluctantly concur. Why are there no non-DNA lifeforms around today? Because they all died out? The stromatolites didn’t die out.
What percentage of all species in the history of life are still extant? I am no expert but I am guessing it is less than 1%. Lots of stuff died in the history of evolution. Additionally I expect there are countless extinct species of which we have no knowledge, as they left no recognizable trace.
Perhaps my precursors couldn’t handle the oxygenation of the atmosphere or some other massive change.
Perhaps they are still here, and we’ve not found them, perhaps because we aren’t looking properly.
I would almost find it easier to believe in intelligent design rather that believe that there are no evolutionary precursors to DNA. Call it an argument from incredulity if you like but I’m not buying into either.
Counting viruses, bacteria, algae, diatoms and other very simple life forms – I don’t believe anyone has a number, or percentage, of life forms that have come down to us from near when it all started. The oxygenation of the atmosphere apparently began when photosynthesis kicked off – this is some time after the appearance of the very first life forms, but it doesn’t appear that anyone knows what “some time” means in this context. According to the experts the non-DNA life forms are not here and yes they have been looking – very carefully, for the obvious reasons we are discussing.
I’d prefer to support the idea of DNA evolving very rapidly once the replicating polypeptides (or whatever ) got going at a certain threshold of sophistication.
It could well have been an extremely localised affair – some analogue of Dawin’s warm little ponds – but only a very small number of ponds.
We don’t see the evidence today because we haven’t found the one pond where it actually happened.
DNA didn’t just pop into existence – unless you’re invoking panspermia, which clearly you’re not.
“I can’t see DNA simply springing into existence without precursors.”
“DNA didn’t just pop into existence – unless you’re invoking panspermia, which clearly you’re not.”
Just because you personally can’t see it, doesn’t preclude that from being what actually happened, extremely unlikely as it is. Carl Sagan’s book is very strong on this point. Where’s your evidence? You don’t have any – hence what you are proposing is pure speculation and ” gut feeling” – not a very scientific approach.
I did say I sounded like I was doing an argument from incredulity. 🙂 There isn’t a great deal of material evidence from the early times – which invites a lot of speculation.
Evolution by natural selection has been proven time and again as a very good technique for building complexity from humble beginnings – I don’t think it is unreasonable to speculate it had a hand in developing the framework of life. That’s no less scientific than saying “it must have happened this way because there’s no evidence to the contrary”.
I don’t think science has the answer to this one yet. More time needed.
Your last sentence is at least correct. We can speculate about many things, telekinesis, astrology, spoon-bending – speculation without at least SOME/ANY evidence of what you are speculating just ain’t worth much.
Maybe we’re both wrong
http://www.newscientist.com/article/mg21528795.500-dna-could-have-existed-long-before-life-itself.html
Life started with DNA _and_ you can brew it up in the lab yourself…
Don’t think so – doesn’t the article say that it could have been DNA from the start, no precursors?? Interestingly Jack Szostak is one of the experts I spoke to at Stamus. The RNA/DNA chicken and egg question has been around for years, again there’s no scientific proof regarding one or the other. Common-sense says that the RNA came first, but we know how good common-sense is when it comes to things like Quantum Mechanics (and possibly complex Organic Chemistry).
Yes, it does say it could have been DNA from the start – but if that chap can brew it up in his lab, what does that say for the chances of it occurring elsewhere in our galaxy?
Ahh – that’s what you meant 🙂 Now that IS a very good point. YES – and it now gives me hope that even if we carry our greed and stupidity through to extinguishing all forms of life on THIS planet, we won’t actually be extinguishing the only centre of Life in the whole Universe. Yes – that is truly GREAT news!!!!
Now where is your evidence that life on other planets isn’t as greedy and stupid as us? 🙂
That is of course true – but if life out there is more common than my original reckoning – we can but hope that at least one civilisation makes it into old age 🙂
I doubt the panspermia hypothesis explains the origin of DNA simply because the Fermi paradox indicates that life in our galaxy is so very rare, it is highly improbable. Note the evidence of the argument given with the argument. Nor do I believe we can look to evolution to explain this mystery. This sort of quote is found in many places in the literature, “The chief defect of the Darwinian theory is that it throws no light on the origin of the primitive organism—probably a simple cell—from which all the others have descended. When Darwin assumes a special creative act for this first species, he is not consistent, and, I think, not quite sincere…» wrote Haeckel in 1862 in a footnote in his monograph on the radiolaria (Haeckel 1862)”. The best explanation is that there may be millions of planets with conditions just right for life to form, and out of those millions, a very few, perhaps only one got it just right. This is simply a version of the weak anthropic principle, which is already widely accepted in cosmology. So, if you have millions of planets, with billions of hurricanes blowing through junk yards for hundreds of millions of years, yes, perhaps some form of a primitive clock comes together in one of them somewhere. As far as we have been able to discover, it never happened again, here or anywhere else. A rare event to be sure, but not impossible, obviously, since it had to happen somewhere to allow for our existence.