Which is an example of evidence of evolution based on comparative biochemistry?

I believe is the fact that sheep insulin can be substituted for human insulin is an example of evolution based on comparative biochemistry. Comparative biochemistry is an evidence of evolution simply because by comparing DNA and RNA we are able to see how closely related organisms are. it is important to note that biochemistry is the study of the basic chemistry and processes that occurs in the cell. 

Try and make the question more clear : )