In nature we find not only that which is expedient, but also everything which is not so inexpedient as to endanger the existence of the species.

A man sufficiently gifted with humor is in small danger of succumbing to flattering delusions about himself, because he cannot help perceiving what a pompous ass he would become if he did.

Every man gets a narrower and narrower field of knowledge in which he must be an expert in order to compete with other people. The specialist knows more and more about less and less and finally knows everything about nothing.

Truth in science can be defined as the working hypothesis best suited to open the way to the next better one.

Man has been driven out of the paradise in which he could trust his instincts.

Man appears to be the missing link between anthropoid apes and human beings.

The instinctive need to be the member of a closely knit group fighting for common ideals may grow so strong that it becomes inessential what these ideals are.