When learning evolution in high school, we generally examine the morphological results of the changes in the genetic code (Galapagos' finches beaks, for example.). Evolution of molecules is an especially fascinating topic as it brings evolutionary principles closer to the chemical source of diversity. In the classroom lesson section there are suggestions for using online databases of molecular sequences for various organism's protein chains to explore evolution of insulin across taxa.
Long before mammal evolution, or even vertebrate evolution, insulin evolved. It appears to have been a chemical messenger
among
bacterial cells indicating food was available in the general area. It later became the molecule responsible for regulating organismal blood sugar.
Different species do not have identical amino acid sequence, but the location of disulphide bonds, both ends of the A chain, and other features allow the protein molecule to assume the same conformation so it can perform the same job.
Diversity is generated by variations in the genetic code. Amino acids in the protein molecule may substituted as a result of mutations to the DNA. While these are subtle differences in the insulin molecule, the functional regions remain unchanged. However, in the case where these mutations caused the insulin to be nonfunctional, the organism did not live to pass on this mutation. In other cases, the mutation resulted in a change that did not have a deleterious effect on the function of the molecule. In this case, the mutation remained with the organism and may be passed on to the next generation.