J. B. S Haldane, Julian Huxley, Animal biology, 1927
“The one great difference between man and all other animals is that for them evolution must always be a blind force, of which they are quite unconscious; whereas man has, in some measure at least, the possibility of consciously controlling evolution according to his wishes.”
I have found the quote in Lee Alan Dugatkin, The Altruism Equation, Chapter Four, J.B.S: The Last Man Who Might Know All There Was to Be Known.