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I think we are talking about a particular effect not just any effect. It has to have an effect on which creatures reproduce and which don't, I think. Some trait that on the face of it seems like a survival advantage might have no effect on which life forms reproduce, those with or those without the trait. It depends on the entire environmental situation and the other traits possessed by the organism. One might even imagine a situation where having vision--which seems like an obvious advantage--might be a negative trait, depending on other factors.
So perhaps it is not a simple matter at all determining which traits are neutral and which not.
Robin,
You are actually dead-on in your question here. It is the nature of mutation that it be random. Whether it is neutral, beneficial, or harmful is more often than not a factor of the environment. Obviously a mutation that causes a zygote to abort during somite formation is harmful and impossible to be passed onto the next generation. But more often mutations are not as easily classifible.
The same mutation can be neutral in one environment, while being beneficial or harmful in another. I am sure there are better examples out there, but one that comes to mind are mutations in cell transport proteins in Nucella snails (I am going from memory here). In the general population there is a mutated protein that enables the snail (because of it's ability to transport material in and out of the cell) to function in warm temperatures. In the majority of the snail's range the gene that codes this protein exists and seems to arise frequently and is neutral. During warming events (like el Nino) the gene is favored. During cold events (such as when the cold-phase Pacific Decadal oscillation coincides with non-el Nino years) the gene is not favored (the daughter protein doesn't function as well as the standard protein). So the same mutation is usually neutral, but can be beneficial in warm water and detrimental in cold water. I am searching for my refs on this, but they seem to be buried. I suspect that many EvC people have even better examples.
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So the term "imperfect replication" does not mean the same thing as "sexual recombination"?
Mutation (imperfect replication) is not the same sexual (genetic) recombination, although both can have selective consequences. Mutation refers to an accident in a gene that results in a new sequence (usually tiny, insignificant, and often lost or repaired but can be none of the above). Genetic recombination is when whole genes are mixed during sexual reproduction and different alles may be expressed.
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One does get mixed signals on this forum.
I can see where you get this (at least on this topic) but try to understand that the concept itself is pretty complicated, and there are many different terms that are used. Often these terms differ in meaning between scientists and laymen. In my opinion you have asked good questions on this topic.
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Elim Garak: "My dear Doctor, they're all true"
Doctor Bashir: "Even the lies?"
Elim Garak: "Especially the lies"
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