Cytachrome C and neutral drift

As the different versions of Cytachrome C all do the same thing, transport electrons, the existence of different versions in different species is due to neutral drift, right?
Is yes then I have a follow up question.

OK just to speed things up a little, I will assume that we agree that the different versions of Cytachrome C we see in different species are due to neutral drift.Why then do we not see different versions of Cytachrome C within species? (if this is correct which I underdstand it is).
Shouldn't we see different versions within species as a result of neutral drift within species?

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First, just because all versions of cytochrome C do basically the same job, it does not follow that there are no functional differences between them. For example (based on zero knowledge of the details of this particular protein), two versions might function best at two different temperatures. So more than drift might be involved -- but most of the observed differences probably are due to drift.
  —sfs

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So if they are functionally different and even some differences are not due to neutral drift, can Cytochrome C be used as evidence for common descent?

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I don't understand what the issue is here? Could you explain what the perceived problem is?

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I was under the impression that the various versions of Cytochrome C were used as evidence of common descent. That they display a kind of nested heirarchy.If there is no evidence that Cytochrome C does in fact undergo neutral drift within species then this may question whether it ever really neutrally drifts at all, and hence whether it can be used as evidence for common descent.I may misunderstand some things here but if you have the time I will try to pay attention to any help you can give.

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To make something that has been implied already clearer the rate at which cytochrome-C changes is slow - it is less frequent than speciation.

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That is not to say that it does not vary within ANY species but it does mean that we might have to look hard to find an example - and there may not be one at the current time.

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What about sharks? Haven't they been around for an awful long time?
They should have been around for long enough to display variation.It certainly does seem a very weird coincidence if these varaitions only are within species if we take animals like sharks into account doesn't it?This is is what you seem to say is true that there may not be any real varaitions within species compared to those between species.

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Hopefully this is helpful, let me know if you have questions.

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Firstly thanks for all the replies.I was looking at a creationist site so i wanted to check the ideas there.http://www.evolutionisdegeneration.com/...ption.htm#6.4.2.9gAs you can see

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The fact that a protein like cytochrome c differs between non-related species, but is the same within one species, shows that the non-related species do not have a common ancestry. The point of the different versions of cytochrome c is that they all do the same thing: transport electrons. Natural selection can thus never choose one version over another, because they all do exactly the same thing. A term has also been thought up for that: neutral drift. But it is then strange that different versions of cytochrome c are not also found within the same species (such as perhaps the sharks, which have not changed in millions of years)! It could be called extraordinarily coincidental, if not to say miraculous, that these neutral changes always and only take place around the diverging of two species. What does that indicate? Either the non-related species have no common ancestry and each species received their own variant of cytochrome c, which then theoretically (or by genetic manipulation) could change. Or cytochrome c, in combination with the protein with which it reacts, does not permit any mutations, which means that the non-related species do not have a common ancestry. (This was concluded earlier, but now we see it confirmed in practice.)

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This creationist seems to argue that Cytachrome C indicates common descent is not true, but it is difficult for me to know whether what he writes is correct as I am an amateur in this area.