"In thinking about what the human animal might have gone through in the evolutionary process, have you wondered how some of the small changes which must have occurred could have had survival value? Haven't you wondered how they could have survived, when, in all of our experimental work every small change we make dies? … How many changes must have occurred in the human eye, occurred and died, before one change came along — an apparently trivial change … that gave the whole animal a significant increase in its power to perceive and hunt down its enemies and find its food. This is the kind of change that survives."