Do only advantageous mutations fuel evolution?

That all depends on teh environment.

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I hunt for the truthWhat you can do in my country and get away with:Softdrugs? Legal!
Legal drinking age? 16!
Birth control (the pill)? Free!
Gay marriage? Legal!
Abortion? Legal!
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Age of consent? 16 (14 if you have the parents permission)!Yep, only one way down for us!

Well, clearly a mutation can only be called advantageous or deleterious with hindsight. A mutation is advantageous if it has conferred (note the the use of the present perfect tense here) an advantage to the organism.

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"Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin.

That which survives in an environment is beneficial by definition. That which perishes in an environment is deleterious by definition.
When you go shopping you pick the best fruits and vegetables available to purchase.
It is all relative to what else is around to compete.
I might be able to kick snot on an elementary school kid(deleterious) but be placed in my casket by Mike Tyson(beneficial).
Again as I understand it.

Is there then, no real such thing as a netral mutation?

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Always wanting to hear other peoples opinions about God and evolution. Email me.

That's too hasty a conclusion. Neutral mutations are possible. For example, there is such a thing as junk DNA, which is generally not expressed. How this junk DNA got into the genome is another story, but if a mutation happens in a piece of junk DNA, nothing happens as a result of it.Another example of a neutral mutation would be a mutated codon that codes for the same amino acid as the original codon. Take the amino acid Alanine for example. The codon GCA codes for it. If the A is mutated into a G you get GCG. This also codes for Alanine. The resulting protein would be the same in either case, and you wouldn't notice the mutation in the organism that has it.

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"Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin.

I think that Shalamabobi is mis-stating the case by oversimplifying it. There are reasons why neutral and even deleterious mutations can survive in a population, such as genetic drift. Similarly beneficial mutations can be lost by drift. But it is true that what we consider beneficial mutations are those that tend to increase in frequency in a population due to selection, potentially up to the point of fixation.The only way to actually measure the beneficial effect of a mutation is from post-hoc measurements as Parasomnium pointed out.Most mutations are considered neutral, or nearly neutral, but I would suggest it is not possible to definitively show that there is no possible environment in which a particular mutation might have some beneficial, or deleterious, effect. It is however possible to identify many mutations which have little or no likelihood of having an effect, such as in-frame nucleotide substitutions in a protein coding gene which do not affect the amino acid sequence they code for. Even as I write this I am thinking of scenarios where such a mutation could indeed be non-neutral, but I still think there are lots of cases where we can be confident that the mutation will be neutral in most forseeable environments.TTFN,WK

Expression is not the be all and end all of genomic function. There are probably multiple non-expressed sites in what has been considered putative junk DNA which have a functional role, one already identified group of such regions are the 'conserved noncoding elements' (CNEs)(Woolfe and Elgar, 2008). Although as yet the functional roles of all these regions are not clear some have been shown to mediate regulation of nearby genes (Sabherwal et al., 2007).TTFN,WK Edited by Wounded King, : No reason given.

Wouldn't that be a form of expression as well, although indirect?

Its the regulation of expression but the sequences themselves are never expressed.You might argue that as functional elements these aren't junk DNA but unfortunately the term is so plastic that there is no easy way to draw a distinct line between what is and what isn't. We suspect that most CNEs have function (or else why are they conserved?) but is conservation enough to mean that a region should no longer be considered junk?Personally, I don't like the term 'junk DNA'. Its especially unfortunate that so many creationists/IDists seem to have decided that somehow some 'junk DNA' being functional is proof of (divine) design.TTFN,WK

If the raison d'etre of some piece of DNA is the regulation of neighboring pieces, then if it does so, that would constitute its expression, right? (We are nit-picking after all... Just ignore this.) Because they're good at causing themselves to be copied? Most "functional" genes use the complete organism as a means to get themselves copied and spread around. Maybe the CNEs are just hitching a ride? (Selfish gene talk, Dawkins and all that.)

I can't really ignore this, it totally redefines the whole concept of gene expression. A gene is 'expressed' when it is transcribed as mRNA from its DNA template, and in canonical cases then translated into protein. To use 'expressed' in some other way is only going to confuse any familiar with molecular biology. You seem to be conflating gene expression and function. Being copied is a distinct mechanism from being conserved. There are some 'junk' elements that lend themselves to increased copying, especially highly repetitive sequences where slippage can occur leading to duplications, but CNEs are usually identified from datasets where such repetitive elements have already been screened out. There still needs to be something acting to maintain the conserved sequence from simply degrading. These sequences are not like ERVs or other remnant proto-viral sequences which can sometimes proliferate through reinfection.If this were merely a case of nearby sequences hitching a ride with selected genes then why do CNEs form islands of such high conservation, why aren't the other nearby sequences conserved?The fact that we are identifying regulatory functions for CNEs suggests that what is going on is more directly relevant to organismal development/evolution than an artifact of genetic hitchhiking.TTFN,WK

That would be because shalamabobbi doesn't know that much about it yet. Thanks for all the great input. This site has been very helpful and sets a very high standard. Not all of us are unappreciative of the time spent here by busy scientists. I alas am a lowly engineer but the choice was sort of a toss up for me.

I think some of the obtuse people i have discussed with on the evolution topic should give this forum a try!You go quite in the core of the matter here