A vital reservoir......................

 Nature was not as hungry to homogenize genetic variation as human eugenicists had presumed.  Indeed, Dobzhansky recognized that natural variation was a vital reservoir for an organism—an asset that far outweighed its liabilities.  Without this variation—without genetic diversity—an organism might ultimately lose its capacity to evolve.

-Siddhartha Mukherjee,  The Gene:  An Intimate History