To quarrel with the uncertainty that besets us in intellectual affairs would be about as reasonable as to object to live one's life with due thought for the morrow because no man can be sure he will alive an hour hence.

It is better to read a little and thoroughly than cram a crude undigested mass into my head, though it be great in quantity.

The rules of the game are what we call the laws of nature.

Extinguished theologians lie about the cradle of every science as the strangled snakes beside that of Hercules; and history records that whenever science and orthodoxy have been fairly opposed, the latter has been forced to retire from the lists, bleeding and crushed if not annihilated; scotched, if not slain.

Regarded anatomically, the resemblances between the foot of Man and the foot of the Gorilla are far more striking and important than the differences... be the differences between the hand and foot of Man and those of the Gorilla what they may the differences between those of the Gorilla and those of the lower Apes are much greater.

It is an error to imagine that evolution signifies a constant tendency to increased perfection. That process undoubtedly involves a constant remodeling of the organism in adaptation to new conditions; but it depends on the nature of those conditions whether the direction of the modifications effected shall be upward or downward.

The birth of science was the death of superstition.