Why can comparisons of protein similarity between species can reveal the degree of genetic kinship?

If descent with modification is correct, the protein structures are passed on from one generation to the next. The closer the protein structures are to the protein structures of another species the closer the genetic relationship can be be assumed to be.

There was great excitement in looking at the protein structures in order to determine the evolutionary descent and relationships. However the research has not worked out. The protein structures of cytochrome C and others shows groups of related species all equal distant from each other. ( Denton Evolution a theory is Crisis)

Another example is the protein structures of pigs and humans. The heart values of pigs have turned out to be the closest to the protein structure of humans. Apes and Chimps that were thought to be the best sources of organ replacements for humans due to supposed genetic kinships cause massive rejections and are no longer used.