Dr. Jules Hilbert: Hell Harold, you could just eat nothing but pancakes if you wanted.Harold Crick: What is wrong with you? Hey, I don't want to eat nothing but pancakes, I want to live! I mean, who in their right mind in a choice between pancakes and living chooses pancakes?Dr. Jules Hilbert: Harold, if you pause to think, you'd realize that that answer is inextricably contingent upon the type of life being led... and, of course, the quality of the pancakes.

The fundamental biological variant is DNA. That is why Mendel's definition of the gene as the unvarying bearer of hereditary traits, its chemical identification by Avery (confirmed by Hershey), and the elucidation by Watson and Crick of the structural basis of its replicative invariance, are without any doubt the most important discoveries ever made in biology. To this must be added the theory of natural selection, whose certainty and full significance were established only by those later theories.