The study of similarities and differences in the proteins and molecules that control life processes.
Some important molecules are highly conserved among species, so slight changes can cause death.
If variations occur outside of these molecules functional region they are called neutral.
So their accumulation is not affected by natural selection and occur at a fairly regular rat.
Scientists can study the DNA base sequence or order of amino acids in a protein and estimate the time at which the 2 species last shared a common ancestor.
