>What Yockey did was substitute hydrophobics for hydrophobics, hydrophyllics
>for hydrophyllics. These are unlikely to alter function. Then he calculated
>the useful ones.
I realize what Yockey did. At our present state of understanding of the
effects of amino acid substitution on protein shape, and thus function (it
is not until this year that we had serious tools for tackling this
question), I would say that estimations based on Yockey's criteria are
meaningless. Having said that, I would quickly add that an unspecialized
protein like cytochrome c probably can take a lot of hits and still be
viable. Maybe even enough hits so that every human being who ever lived
could have a different viable cytochrome c. But the fact that we all have
about the same molecule says that there is an optimum form for each
organism and that is the basis for the observed differences. Studies on
mice living in the vicinity of Chernobyl showed that they all were running
around with variants of cytochrome c, so there must be a gob of the
possible number that are viable in any case.