The amino acid sequence of a protein is unique to a species and is similar among the species that share common ancestry. The more conserved the sequence between any two organisms, the higher the likelihood that they originated from a common ancestor.
There is a lot of redundancy in the amino acid sequence of a ubiquitous protein like Cytochrome C and there are about 10^93 different possible sequences for it. This implies that all the different organisms can theoretically have different amino acid sequences, if there is no evolution.
A comparison of human and chimpanzee's amino acid sequence of Cytochrome C show that the sequence is exactly the same. A comparison of human cytochrome with that of other mammals show a difference of only about 10 amino acids. Statistically, this would be almost impossible (probability of 1 in 10^29) without shared ancestry. This also shows that compared to other mammals, chimpanzees are our closest relatives. The fact that we are different from chimpanzees, even though we originated from the same ancestor, is simply a result of evolution.
The comparison of amino acid sequences, thus, supports the evolutionary hypothesis.