Evolutionary change at the molecular level, especially regular gradual change in DNA which may indicate the relative timing of genealogical divergences.

the process of making discrete changes in genes to improve the functional characteristics of proteins and enzymes.

Molecular evolution is the process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960's as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure and function of nucleic acids and protein. 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.