cytochrome c and natural selection

[hatsoff]

In one of her anti-ID lectures, Eugenie Scott mentioned a protein called cytochrome c, which is apparently very useful in cladistics. Among other things, she explained that we should expect the same molecular divergence between all the modern organisms in two branching clades. For example, cyt c in amphibians and mammals should all be equally removed from fish, since they are part of the same branching clade from fish.

This puzzles me on two counts:

1) What is cytochrome c, that it can evolve into a different molecule which we still classify as cytochrome c? Do the different versions of cyt c have different functionality?

2) If different versions of cyt c have different functionality, then that means natural selection acts on cyt c, which in turn means (as far as I know) that we cannot expect cyt c to have similar rates of evolutionary change between different clades.

My understanding is that only if molecular variations in cyt c have no impact on functionality would I expect equal molecular divergence among all organisms in a particular clade, because only then would evolution be random, and subject to the law of large numbers when comparing molecular variation. If cyt c changes are selected by nature, then that means different clades will be subject to different environmental pressures, resulting in different rates of change and therefore different amounts of total molecular divergence.

Any help would be much appreciated.

[David George]

http://en.wikipedia.org/wiki/Cytochrome_c
This can answer your first question.

Its not a real necessity for the Cytochrome c to evolve since its such a good protein that it got "stabilized" .
I am not too sure of the molecular divergence question.I need to work on it more to know about it.

You can really appreciate cytochrome c if you align the amino acid sequences in a program like CINEMA.You can get the amino acid sequences from NCBI and align them and see one of the most conserved proteins in a colourful format.
Even cytochrome b looks pretty conserved.
So may be its common to some cytochromes also.