Original: Some of the key topics that spurred development of the field have been the evolution of enzyme function, the use of nucleic acid divergence as a "molecular clock" to study species divergence, and the origin of non-functional or junk DNA.
Simplified: Some of the key topics have been the evolution of enzyme function, the use of nucleic acid changes as a molecular clock to study species divergence, and the origin of non-functional or junk DNA.