Boredom is a vital problem for the moralist, since at least half the sins of mankind are caused by the fear of it.
Even in civilized mankind faint traces of monogamous instinct can be perceived.
What science cannot tell us, mankind cannot know.
Mankind has become so much one family that we cannot insure our own prosperity except by insuring that of everyone else.
It is not by delusion, however exalted, that mankind can prosper, but only by unswerving courage in the pursuit of truth.