If we (researchers) should keep the environment of boys and girls absolutely similar these instincts would produce sure and important differences bet… - Edward Thorndike

Psychology is the science of the intellects, characters and behavior of animals including man. Human education is concerned with certain changes in the intellects, characters and behavior of men, its problems being roughly included under these four topics: Aims, materials, means and methods.

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 to improve man's environment as to improve his nature.

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.