The following proposition seems to me in a high degree probable—namely, that any animal whatever, endowed with well-marked social instincts, the parental and filial affections being here included, would inevitably acquire a moral sense or conscience, as soon as its intellectual powers had become as well, or nearly as well developed, as in man. For, firstly, the social instincts lead an animal to take pleasure in the society of its fellows, to feel a certain amount of sympathy with them, and to perform various services for them.

...I believe there exists, & I feel within me, an instinct for the truth, or knowledge or discovery, of something of the same nature as the instinct of virtue, & that our having such an instinct is reason enough for scientific researches without any practical results ever ensuing from them.

I never gave up Christianity until I was forty years of age.

Not one change of species into another is on record ... we cannot prove that a single species has been changed.

The most important factor in survival is neither intelligence nor strength but adaptability.

Freedom of thought is best promoted by the gradual illumination of men’s minds which follows from the advance of science.

Thus we have given to man a pedigree of prodigious length, but not, it may be said, of noble quality.