A Question About Evolution and the Genetic Code

[Primvs Sextvs Loverlord]

Summarizing the state of the art in the study of the code evolution, we cannot escape
considerable skepticism. It seems that the two-pronged fundamental question: “Why is the
genetic code the way it is and how did it come to be?”, that was asked over 50 years ago, at the
dawn of molecular biology, might remain pertinent even in another 50 years. Our consolation is
that we cannot think of a more fundamental problem in biology.

Source: http://arxiv.org/PS_cache/arxiv/pdf/...807.4749v2.pdf


Can someone explain in layman terms what it is about the genetic code that they're talking about here and why it's not compatible with the theory of evolution?

From what I had always known, the study of the genome, if anything, confirmed evolution.

Thanks!

[Elfdude]

It does help prove evolution of species from a common ancestor. However as it was stated our idea about how DNA arose to be used by life is through deduction not factual knowledge. Until we produce life in the lab with our predicted criteria (which we are close to doing but not quite yet) it remains uncertain. For all we know our ideas could prove to be horribly wrong. However I don't think that paper is anti evolution, if anything it's the opposite.

This is similar to the problem of gravity or cosmology or any other field of science, it's an issue that is science's real current goal in solving. Eventually we'll get past it just like every other problem I'd presume.

[Sphere]

The problem is this: once DNA exists, evolution works beautifully and explains essentially all observations and evidence we have for the living history of Earth (except for some recently discovered proteins that "reproduce" without DNA).

The question is how do you get from simple organic molecules to DNA. Theres been a lot of research, and indeed there have been some successes at creating amino acids in natural conditions (iirc) but there still is still a gap in our knowledge on how full fledged DNA arose. What makes it tough is that we can never expect to have direct evidence of what this process was, and we can only glean scant understanding of the environmental conditions involved, the chances of finding the answer are fairly slim.

[Vizsla]

Can someone explain in layman terms what it is about the genetic code that they're talking about here and why it's not compatible with the theory of evolution?

From what I had always known, the study of the genome, if anything, confirmed evolution.

The genome and the genetic code are two different things.
The (human) genome is our DNA.
The genetic code is the code all living cells use to translate the information encoded into the DNA into paricular amino acid sequences in proteins.
http://en.wikipedia.org/wiki/Genetic_code

This is a review paper. They are summarising the current state of knowledge regarding the genetic code.
I think you should start with lower level molecular biology and work your way up to this stuff.
Their basic question: How come we have this particular code?
Their final answer (that you have quoted above): We're still not sure but we're working on it.

I think they finish with that because that's the kind of thing you're expected to say in conclusions.

There's a bit where they say the code we have is not the best at preventing errors.
It could be we have the one we have by chance.
Maybe one particular breed of tiny single celled organism, which happened to have this code, beat all of the other kinds.
Or maybe Early Life selected this genetic code for some reason we haven't thought of yet.

It is quite likely we will never know why we have this genetic code.
I don't imagine that will stop the research grants flowing, though.

[Phier]

Source: http://arxiv.org/PS_cache/arxiv/pdf/...807.4749v2.pdf


Can someone explain in layman terms what it is about the genetic code that they're talking about here

The interesting thing about the genetic code is that it is (almost) universal in all organisms. AUG in you and a fruit fly still codes for MET. And while there are several theories why this is, none of them answer the question fully. One idea is that the code is what it is because certain molecules were more likely to link with other amino acids so the code was basically determined by chemical affinities. This has been demonstrated to an extent but is too weak. Another idea is that the code evolved to be the most stable to resist mutations, and while the code IS stable, its by no means the most stable possible code, some could be much better. Another idea is that the code is a complete accident but once established, changing it would be very difficult without massive mutation (and death) of the mutant so its 'frozen'. Another is the coevolution theory where the code developed as biologic path ways matured that could produce certain amino acids.

My take is that it is a combination of the 'frozen accident' theory and the adaptive robustness theory, which a touch of selection. One thing I didn't see mentioned, though I may have missed it, is that if a code is TOO robust you won't see many mutations. This would be an evolutionary dead end from the start. I think you need enough robustness to the code that normal replication takes place, with enough room for mutation for evolution to take place. Imagine three organisms, one with a code that was very easy to mutate, one that was kinda hard, and one that was very hard to mutate. They are living in the same pond, now the easy to mutate one might get a competitive edge via mutation over the other too, but its suffering a cost of many non-viable or worse organisms produced by its weak code. Now lets take the hard to mutate one (that would be life as we know it). It normally produces 'true' but every now and then lets a mutation slip by, sooner or later it develops a superior advantage over the other two, but without as much cost as the easy mutator, while the advantage the very hard mutator gains over the hard mutator (us) is quickly swamped out by the superior strain. In the end the easy mutator and the very hard mutator go extinct.

This doesn't explain why we have exactly THIS code, only the type of code which is middle of the road in robustness.

and why it's not compatible with the theory of evolution?

Whoever said that doesn't understand the paper themselves, so if someone told you that feel free to pimpslap them.