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One of the most useful advances has been the development of molecular biology.
In this field, scientists look at the proteins and other molecules that control life processes.
While these molecules can evolve just as an entire organism can, some important molecules are highly conserved among species.
Changes that do not affect functionality are called "neutral substitutions" and their accumulation is not affected by natural selection.
As a result, neutral substitutions occur at a fairly regular rate, though that rate is different for different molecules.
Glycerol (5-10%) increases the density of a sample so that the sample will layer at the bottom of a gel’s sample well.