Selective breeding can alter man's capacity to learn, to keep sane, to cherish justice or to be happy. There is no more certain and economical a way … - Edward Thorndike

The intellectual evolution of the race consists in an increase in the number, delicacy, complexity, permanence and speed of formation of such associations.

If we (researchers) should keep the environment of boys and girls absolutely similar these instincts would produce sure and important differences between the mental and moral activities of boys and girls.

The statements about human nature made by psychologists are of two sorts,—statements about consciousness, about the inner life of thought and feeling, the 'self as conscious,' the 'stream of thought'; and statements about behavior, about the life of man that is left unexplained by physics, chemistry, anatomy and physiology, and is roughly compassed for common sense by the terms 'intellect' and 'character.'
Animal psychology shows the same double content.