Intelligence is based on how efficient a species became at doing the things they need to survive.

On the theory of natural selection we can clearly understand the full meaning of that old canon in natural history, “Natura non facit saltum.” This canon, if we look only to the present inhabitants of the world, is not strictly correct, but if we include all those of past times, it must by my theory be strictly true.

The more we know of the fixed laws of nature the more incredible do miracles become, - that the men at that time were ignorant and credulous to a degree almost incomprehensible by us, - that the Gospels cannot be proved to have been written simultaneously with the events, - that they differ in many important details, far too important as it seemed to me to be admitted as the usual inaccuracies of eye-witnesses; - by such reflections as these... I gradually came to disbelieve in Christianity as a divine revelation.

As for a future life, every man must judge for himself between conflicting vague probabilities.

Only picture to yourself a nice soft wife on a sofa with good fire, & books & music.

There is no fundamental difference between man and animals in their ability to feel pleasure and pain, happiness, and misery.

we are always slow in admitting any great change of which we do not see the intermediate steps