Even when we are quite alone, how often do we think with pleasure or pain of what others think of us - of their imagined approbation or disapprobation.

I think it can be shown that there is such an unerring power at work in Natural Selection, which selects exclusively for the good of each organic being.

The more one thinks, the more one feels the hopeless immensity of man's ignorance.

In my most extreme fluctuations I have never been an atheist in the sense of denying the existence of a God ... I think that generally (& more and more so as I grow older) but not always, that an agnostic would be the most correct description of my state of mind.

It is so easy to hide our ignorance under such expressions as the plan of creation or unity of design, etc., and to think that we give an explanation when we only restate a fact.

I think it inevitably follows, that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct. The forms which stand in closest competition with those undergoing modification and improvement will naturally suffer most.

Even people who aren’t geniuses can outthink the rest of mankind if they develop certain thinking habits.

It has sometimes been said that the success of the Origin proved "that the subject was in the air," or "that men's minds were prepared for it." I do not think that this is strictly true, for I occasionally sounded not a few naturalists, and never happened to come across a single one who seemed to doubt about the permanence of species.