Discussion of everything related to the Theory of Evolution.
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I know this is the evolution section,however this topic seems to fit the theme so, Is abiogenisis natuarally possible? or was it a miracle?.
Btw,please explain in laymen how and when this happened.
thanks in advance.
abiogenesis is definitely possible, and as a scientist you have to assume this is what happened.
First of all, don't confuse abiogenesis with spontaneous generation - abiogenesis was a gradual process that took millions of years.
How exactly it happened we will never know - after all, no one was there to see it. What scientists can do is provide a possible explanation. Basically say: "look, I can prove this way was physically possible, and since life had to come about at some point this is most likely how it happened".
Of course, this is a whole field in itself. So I can't explain it here. However, in a nutshell, what happened was most likely this: fatty acids formed abiotically around geysers. We know fatty acids can self-assemble into lipid bilayers completely by themselves, without any information or energy needed. Probably some sort of RNA-like polymer made its way inside the lipid vesicles. this polymer had two properties: it was able to copy itself (acting like an enzyme) and also the ability to store the information necessary for its own synthesis. polymers that are better at replicating would then be favored in a darwinian selection-mechanism, allowing for evolution by natural selection to start.
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter
You might want to read this week's New Scientist in which an article called "another kind of Evolution" suggests that at the very early stage of life - horizontal transfer of genes and not Darwinian selection was the prime mover.
Hmmm... Do you have any sources for this? I've never heard of a geyser hypothesis, and as far as I know lipid synthesis came later in chemical evolution. Yes, phospholipids will spontaneously form micelles and vesicles. However, this actually never happens in biological systems. All such forms are grown off of already existing lipid membranes. This suggests to me that a great many things in cells were in place before lipid membranes evolved, which means there must have been another way to compartmentalize and concentrate precursor molecules so they could react and transition from geochemistry to biochemistry. Also, if you have lipids forming first, there is the difficulty of getting a living system into a phospholipid "bubble".
The best, most comprehensive hypothesis I have read for abiogenesis is Martin & Russell's Alkaline Hydrothermal Vent hypothesis. This is a nice recent overview of the idea:
Basically, the gist of it is this: Hydrothermal flow basically has water being taken into and through the crust, where it is heated and any compounds in it may interact with the crust as it flows there. It then comes out at hydrothermal vent systems. Many vents, such as black smokers, are very hot, and while current life has evolved to take advantage of them, it is unlikely that they were friendly to the kinds of reactions necessary to originate life. However, there are cooler hydrothermal vents more inline for reactions that can synthesize some pretty complex organic molecules, including precursors to many of the biomolecules.
It is hypothesized that at vents like this on early earth (perhaps as early as 4.2Gya) alkaline hydrothermal fluid rich in various precursors flowed out of the vents and through porous rocks of Iron and nickel sulfides. These rocks naturally have microscopic, semipermeable cell like compartments which, when water flows through them, can serve to concentrate macromolecules in that water. Oceans at this time were acidic, due to the large amount of CO2, so there was a pH gradient causing a proton-motive force (like the gradient across your mitochondrial membranes) at the vent-ocean interface. There was also a thermal gradient. So, essentially there was exactly what was needed for life to begin: a constant source of raw materials, a constant source of energy, reaction surfaces to help catalyze reactions, and a means of concentrating the materials so that newly formed molecules did not just diffuse into the ocean. For a good visual, take a look at the illustration on the second page of this article:
Some parts (such as the divergence between archaebacteria and eubacteria before the evolution of membrane synthesis) are still somewhat controversial and very open to debate, but the general hypothesis is fairly sound. Mind you, this is not the definitive answer to abiogenesis, but it is, in my opinion, the most comprehensive and currently best supported hypothesis, and it solves a lot of problems that other hypotheses had (such as the concentration problem, the compartmentalization problem, the energy problem, and the raw materials problem).
For a more complete (though perhaps difficult to read if you are not a biologist) look at these hypotheses, I recommend these two papers:
The first paper is the original complete synthesis of ideas for a nice overview of this hypothesis all in one package. It is a little out of date and some details have changed with new knowledge, but for a starting point it's a good one. The second is a bit more hard core as it is a more detailed look at the types of reactions that were likely to start biochemistry off.
So, in a nutshell for the original poster: yes, it appears that abiogenesis is possible. Is this how it actually happened on Earth? Well, we'll never know, but a feasible, falsifiable explanation is better than no explanation at all, eh?
"Empathise with stupidity, and you're halfway to thinking like an idiot." - Iain M. Banks
Reply to Mr Mistery who said:
"abiogenesis is definitely possible, and as a scientist you have to assume this is what happened."
I say: A true scientist makes no assumptions. What kind of science are you talking about?
Doesn't science make assumptions such as 'there are no miracles', 'the laws of physics are uniform', 'logic and maths are true', 'there are rational explanations for all physical phenomena', 'the universe if comprehensible by the human mind'...those sorts of axiomatic a priori 'rules' of scienctific enquiry?
If the the only logical alternative to abiogenesis is some sort of divine intervention/creation, then science must indeed 'assume' that abiogenesis did happen - the only question then is 'how'. (Even if it happened extra-terrestrially and was transferred to Earth by asteroids etc etc, that doesn't explain how it first evolved 'de novo' somewhere in the universe at some point since the Big Bang')
Mamoru - thank you for your very interesting post. There was a programme recently on British TV which had the presenter travel to the USA, and speak to one of Stanley Miller's students, and he was allowed to test out one of SM's original 'soup-testtubes' and yup, there were the proto-biomolecules, untouched for about fifty years since SM cooked them in his lab. Amazing to see!
There is heaps of data on the internet about abiogenesis.
For example : http://en.wikipedia.org/wiki/Abiogenesis
Here is a youtube reference. http://www.youtube.com/watch?v=U6QYDdgP9eg
As things stand at present, we have a lot of scientific findings which relate to abiogenesis, such as polymerisation of organic molecules using mineral crystals as templates, and the spontaneous formation of vesicles from fatty acids. The way these findings are put together is still a bit uncertain. However, adding all those findings together makes abiogenesis clearly possible. We are no longer defending something improbable.
Even so, I find it very easy, the more I learn about what incredible stuff goes on inside cells, to think, could this really have just arisen all on its own?!! Intelligent Design does become very tempting! I can see why some folk just can't believe there wasn't someone pulling nano-levers!!
The cell really is a seriously impressive piece of natural engineering.
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