Oh yeah. Almost forgot the most important point.
While it is a mistake for abiogenesis opponents to think they can calculate the probability of abiogenesis without knowing the complexity of the process and arrive at odds approaching zero… Abiogenesis proponents make exactly the same mistake in reverse by claiming that, regardless of how complex the process might be, the time span involved is so incredibly huge that the probability of life arising spontaneously approaches one.
As I have said, I am not prepared to argue about the probability of RNA being formed, because I am not an organic chemist, and I think venturing to before descent with modification requires too many assumptions. I think arguing probabilities is futile. In terms of probability calculations, the type I have seen are of the Fred Hoyle type which I think are based on crucial misconceptions of evolution, but this is all after descent with selection. Nothing I have seen concerns the world before evolution.
But, to venture a guess, I would say that it seems that you can synthesize ribonucleic acid from a few simple organic molecules and other inorganic simple molecules like ammonia, carbon dioxide, oxygen, water, and phosphate. This is precisely what our bodies do to synthesize RNA every day. I can also imagine scenarios where some type of simpler molecule, for instance a backbone with nitrogenous bases, is able to catalyze these reactions.
Ribozymes are indeed “evolved” from other ribozymes, and at present are not capable of the complex reactions necessary to synthesize other ribonucleic acids. The field and some of the techniques to make ribozymes (SELEX) are only a few years old, though, so the fact that they have been able to make ribozymes to do what they have I think is pretty impressive.
I try to bring up Thomas Gold in these kinds of threads. His theory, from his book The Deep, Hot Biosphere is that petroleum is a feature of planet formation, not a by-product of life. He is a quite respected scientist, although not necessarily in this area, making this sentence a fallacy (argument from authority). But, he does know how to carry out an experiment, and he believes that his data support his idea. He also believes in a deep biosphere which feeds off of and regenerates the oil, and that there is a lot more oil out there than what we believe. I will say that this introduces some interesting folds to the panspermia debate, both pro and con. Pro, in terms of life not dependent on sunlight may exist in large planetismals which have warm cores and other pieces of matter ejected from a solar system. This may carry life around the universe. Con in that petroleum is a complex hydrocarbon, which could lead to all types of neat organic reactions in the proper environments. All of sudden, starting with petroleum, ribonucleic acid seems a lot easier to make.
Here is a Wired article:
As I said, I can’t argue for or against panspermia. The arguments for it, though IMHO are weak because they are based on probabilities based on assumptions which are impossible to test.
Let me just say that I think that Miller-Urey only showed that it was easy to synthesize amino acids and peptides from ammonia, oxygen, and carbon dioxide, and so forth. I don’t think that one can assume that this says anything about the early atmosphere on Earth. I will say it is compelling that such a synthesis is easy and even almost probable, because I’m sure at some point in some environment these molecules would have been around. Since amino acids and peptides are extraordinarily stable to acidic and basic environments, I think that these molecules could have stuck around for a long time, if necessary.
OK, let’s stick with the panspermia angle.
I don’t see how the Cambrian “explosion” can be tied to panspermia, since panspermia is supposed to occur with bacteria not metazoans.
I think the mistake you are making is emphasizing the “gradual” and “random” nature of selection. There is nothing that says that evolution should be gradual, and natural selection is anything but random.
Anyway, it’s not true that all known examples of speciation have occured under artificial selection. First, define species and then we can decide whether speciation has occured or not. Let’s look at dogs. We say that Chihuahuas and Great Danes are in the same species, but only because gene flow is theoretically possible via intermediate size dogs. Suppose we selected out the medium-sized dogs. Suddenly Chihuahuas and Great Danes are seperate biological species. Speciation isn’t something you can detect as it is happening, only after it has happened, since the isolating factors that created two diverging populations could suddenly reverse and the isolated populations are no longer isolated.
edwino:
Correct, because there may be other mechanisms for amino acids to have formed. This is one of my central points.
In most scientific endevors, Modus Ponens logic applies:
If it rains, then the streets will be wet.
It is raining.
Therefore, the streets will be wet.
Too often I see (especially in the science of biogenesis and evolution) a logical falicy called “Affirming the Consequent”:
If it’s raining then the streets will be wet.
The streets are wet.
Therefore, it’s raining.
This is the mistake that I was trying to point out to Lemur866 who wrote:
Lemur866:
It actually requires that you make additional assumptions, but I’ve heard the argument made before, something along the lines of:
Assumption 1: The seed DNA is very complex with lots of non coding sequences. This would apparently not be expected, pre-Cambrian.
Assumption 2: Non coding sequences facilitate rapid evolution with certain environmental triggers.
Assumption 3: Some event or set of environmental conditions occured at the beginning of the Cambrian period to cause rapid mutation and thus great diversity in the animal population.
There’s probably a lot more to the argument…
The theory of natural selection does explicitly state this. Certainly there are evolution theory variants that are more tolerant of rapid, macroevolutionary transitions.
In the sense that it is not a predictable process and is contingent on a multitude of varying factors… It’s random in the chaos theory sort of randomness.
I had an additional qualifier in my original statement - “observed”. If you know of a counter example, I’d be interested to hear about it.
Ahh… herein lies the rub. There are certainly a number of definitions for “species”. Most serious scientists seem to endorse Mayr’s “Biological Species Concept” - reproductive isolation, for modern populations. Gould and Eldridge have suggested Punctuated Equilibria as an alternate methodology for fossil cases. PE looks at morphological, geographical, and sociological factors to make this determination. The only problem is that 100 thousand years from now a couple of scientists did up the fossil remains of your Chihuahua and your Great Dane and PE says that they would probably be classified as separate species.
Not so. Granted it is unlikely that the gene pools would intermingle from that point on, but it’s not speciation unless you want to apply PE to modern populations. I don’t think Gould and Eldridge would approve of this generalization of their theory.
If, through the process of natural selection or some more radical mutation, the decendants of Chihuahuas and Great Danes were discovered to be in reproductive isolation, then we could certainly say that speciation had occured. But guess what, that speciation event could possibly occur even if the medium sized dogs were still around to facilitate gene pool intermingling.
Unless… you are maintaining that the separation is the thing that triggers the speciation event, but that is exactly my earlier point. Chihuahuas and Great Danes have been in sexual separation for thousands of years, using artificial selection techniques. This is arguably an “amplifier” of natural selection, yet no hint of biological speciation seems manifest.
But then we digress… again…