Few animals display their mood via facial expressions as distinctly as cats.

All scientific knowledge to which man owes his role as master of the world arose from playful activities.

One of the most dangerously vicious circles menacing the continued existence of all mankind arises through that grim striving for the highest possible position within the ranked order, in other words, the reckless pursuit of power which combines with an insatiable greed of neurotic proportions that the results of acquired power confer.

More than any other product of human scientific culture scientific knowledge is the collective property of all mankind.

I believe that present day civilized man suffers from insufficient discharge of his aggressive drive

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.

...he who has seen the intimate beauty of nature cannot tear himself away from it again. He must become either a poet or a naturalist and, if his eyes are keen and his powers of observation sharp enough, he may well become both.