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.

Historians will have to face the fact that natural selection determined the evolution of cultures in the same manner as it did that of species.

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.

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

All the advantages that man has gained from his ever-deepening understanding of the natural world that surrounds him, his technological, chemical and medical progress, all of which should seem to alleviate human suffering... tends instead to favor humanity's destruction.

Philosophers are people who know less and less about more and more, until they know nothing about everything. Scientists are people who know more and more about less and less, until they know everything about nothing.

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