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Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
Check out these compendia of blogginess and comment on them, or anything else that strikes your fancy.
Does it ever stop in Kansas?
http://www.msnbc.msn.com/id/11856589/
Help, I’m confused. I can’t get my mind around the concept of a single common ancestor for all existing life. I don’t understand why abiogenic copolymerization processes (of amino acids) wouldn’t have generated any number of more or less independent lines based on different local intitial conditions. Any science-based comments or links would be greatly appreciated.
You know you want one
http://www.mediatinker.com/blog/archives/009547.html#009547
(way past time for me to stop goofing off)
Since this is a general thread, I’m going to ask for an opinion on something that has been bugging me lately.
Does anyone else have a problem with the term “dogma” in science? For example, the “central dogma” of DNA->RNA->Protein. I’ve been hearing in a lot, most of the time when I thought model or hypothesis would be a better term, and it just always rubs me funny. I’ve just always used the term as kind of believing something without reason, which seems more like a religious term and completely alien to science.
Or am I just being overly sensitive….
Any thoughts?
Alan,
While we wait for the experts, we can perhaps kick that question around a bit.
I’m not sure what you mean by copolymerization processes of amino acids. That seems like a specific mechanism which may constrain what happened. I have come to prefer to see this as a process of evolution from prebiotic to biotic chemistry, where the question there life started is not so relevant. It’s awfully hard to define life, it’s much easier to see evolutionary processes.
In my mind local prebiotic chemical production and selection promotes systems that reproduce, even very unfaithfully, in some manner. Lipid spherical membranes interacting with clay pores have been one such proposal, IIRC.
Anyway, the deciding factor was IMO that some type of RNA life appeared. When it was able to reproduce more it would spread all over the different local reproducing places that used an inferior reproduction.
The selection of which NA’s where used for RNA was either decided then, or in a later similar takeover(s), as long as reproduction were more faithful and/or faster with some order of magnitude. The full amino acid set and DNA could come later, with or without takeovers. There is only place for so many significant increases in reproduction speed.
“able to reproduce more it would spread” – able to reproduce more faitfully it would spread
Could anyone help me identifiy the raving homophobe behind this quote?
I’ve transcribed it from the intro to Clawfinger’s The Faggot in You. The ellipsis means I couldn’t hear what he’s saying.
Torbjorn,
By copolymerization, I mean the reaction of several species of monomers, in this case amino acids, to form a large molecule. IME, teh composition of the molecule is dependent on various factors such as concentration of the various monomers and type of catalyst available, which I would presume would vary among different localities, as well as steric fit among teh monomers and teh catalyst sites. Accordingly, each suitable locality would generate a different spectrum of polymer molecules. While an RNA that could replicate would have a considerable advantage, diffusion of such a molecule to other sites would still take a lot of time, and might not be possible if some sites were physically isolated. Consequently, it still seems that there would be plenty of opportunity for competitive replicators to develop and establish multiple lines of decendents.
Perhaps someone could chime in about factors, such as steric hindrance, activation energy, etc that might restrict the spectrum of molecules that could be produced?
“IME, teh composition of the molecule is dependent on various factors such as concentration of the various monomers and type of catalyst available”
So you are assuming such processes, perhaps specifically on amino acids, would be necessary. Well, as I said, I think that would be restrictive. There seems to be experimental programs with many different types of starter systems; I gave one such example.
If you think RNA by itself diffused, and took to long, then it could have had to wait until it was encapsulated in lipids or some such support system. I guess my point is that if any molecule replicated more faithfully and/or faster with an order of magnitude, it would eventually take over the prebiotic chemistry in every environment it migrated to. There was plenty of time. ;-)
Your main objection seems to lead to that meanwhile another comparatively competitive replicator could emerge. I guess so. That would mean the environment could have had to be fine tuned for us to see a single common ancestor. Ie it would be rather low probability for faithful replicators, but not too low of course. Interesting, but bad. Either it was pure luck that there was only one common replicator, or it could be pure luck that the environment was fine tuned.
Yes, we will probably need some inchiming on this point. :-)
Well, until lately, we’d always build a little set of Dogmas of Quantum Mechanics. This was mostly tongue in cheek. Because of current prevailing cultural trends towards fideism, solipsism, and bullshit sophistry, we’ve stopped doing this for fear of playing to the “science is just another religion” crowd.
That’s the other problem with new agers and fundies — they’re buzzkills.
Well, the term “Central Dogma” gives us a chance to point out that the dogma has been disproven; in this case by reverse transcriptase.
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Dial-an-Atheist
Charlie Brown and the pirates
He’s just a spokesman; he wasn’t in on the action. Good grief.
Alan,
By coincidence (or is it?), the thread about abiogenesis http://scienceblogs.com/pharyngula/2006/03/abiogenesis_isnt_simple.php has a picture that refers to ‘hypercycle’. http://en.wikipedia.org/wiki/Hypercycle redirects to ‘quasispecies’, which seems to answer our problems.
First, it deepens this question since it defines a model for replicating species, which is processbased. So when I said that it’s easier to see processes, I was both right and wrong. :-)
Second, the model defines, by replication and mutation, mutational “clouds” of closely related sequences, called ‘quasispecies’. Mutational clouds as predicted by the quasispecies model have been observed!
Apparently, the model gives a maximal values for mutation rates, and more specifically, it selects _one quasispecies_.