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

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

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.

All living beings have received their weapons through the same process of evolution that moulded their impulses and inhibitions; for the structural plan of the body and the system of behaviour of a species are parts of the same whole.... Wordsworth is right: there is only one being in possession of weapons which do not grow on his body and of whose working plan, therefore, the instincts of his species know nothing and in the usage of which he has no correspondingly adequate inhibition.

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

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.

Most people have forgotten how to live with living creatures, with living systems and that, in turn, is the reason why man, whenever he comes into contact with nature, threatens to kill the natural system in which and from which he live.