Might selective reproductive instability be a factor in evolution?

I am not sure what you mean by “reproductively stable genes”.
Do you mean that some genes are ‘less likely’ to mutate? In that case no. Genes are all all equally likely to mutate.
Furthermore, yes, further mutations could cause another increase in neck length. But at some point, a long neck becomes a disadvantage, for example if the lever principle causes the animal to fall over constantly, or if the heart is not strong enough to pump all that blood to the head, making the animal tumble around all the time. In that case, a long neck would be selected against.
It is not that less mutations happen, it is just that a further neck length increase would be selected against.

I did mean less likely to mutate. Are you sure all genes are equally likely to mutate. I know I read somewhere that the genes of the AIDS virus are particularly vulnerable to mutation. I am not particularly knowledgeable about chemistry, but isn’t it possible that the geometry of a chromosome be such that certain areas are prone to improper combinations.

The reason why HI viri are more prone to have mutated offspring is that the virus body basically only contains a strand of RNA that would then be inserted into the victim cell’s genome. A human genome, in contrast, is part of a complex system of reading and writing, which also includes a mechanism to repair damage to the DNA to a certain extent. A virus does not have such a repair mechanism, which means any mutation it gets is there to stay.
In my opinion, virus genes are just as likely to mutate as mammal genes, they just can not get repaired.

I like to take a bit of a step back from genes when talking about evolution, it just makes things a lot clearer. I think that any mutations that occur to an animal or a virus will stick around if they don’t kill or destroy that animal. If it hinders it in any way then it will eventually kill it somehow and that version dies off completely over time after breeding and more deaths etc.

“Among the mutations might be more reproductively stable copies of the genes, but the unstable copies would have an advantage in being able to cause further increases in neck length. This process would continue until the neck length approached its optimum size, at which point the more reproductively stable copies of the genes would win out.”

I personally think that the mutations happen randomly so its not that the genes will choose the unstable copies for the timebeing until the optimum neck length is reached. Its just a matter of it happening randomly to many of the different giraffes over a long period of time (some with the unstable genes and some with the stable genes) and the ones that lived moved onto the next level, some with longer necks and some without. Then eventually after much mutation and some necks getting even longer and some not, the ones with even longer necks would have started dying due to the negative aspects of having a such a long neck. And the ones with short necks were dying out as they couldn’t get as much food as the others. Then we were left with what we have today.

So I think what you are describing is basically the fundamental part of evolution at its core except its a lot more random.

Sounds like Darwinian theory to me.

@ragingloli, Thanks for the info about RNA and DNA mutation.

I don’t fully understand this article Variable mutation rates , but it seems to indicate that mutation rates can vary depending on DNA sequence.

There are definitely genomic hot spots that are more prone to mutation. This is true in a variety of organisms, such as malaria parasites and humans. Some of this has to do with the sequences themselves, while other factors include chromatin structure and location of histones and other DNA binding proteins. As far as HIV is concerned, its high mutation rate is primarily due to its very high replication rate and low fidelity reverse transcriptase (RNA to DNA converting enzyme).

Thank you all for your comments.

@shilolo, I did a Google search for mutation hot spots and I found some articles about them, but I did not find any that backed my idea that these spots might result in a high rate of evolution. I am beginning to think that this concept may be a bit overly simplistic.