“Such simple instincts as bees making a beehive could be sufficient to overthrow my whole theory.”

“If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.”

“The very essence of instinct is that it's followed independently of reason.”

“To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I confess, absurd in the highest degree...The difficulty of believing that a perfect and complex eye could be formed by natural selection , though insuperable by our imagination, should not be considered subversive of the theory.”

“Besides love and sympathy, animals exhibit other qualities connected with the social instincts which in us would be called moral.”

“Hoe al die absurde gedragsregels en al die absurde geloofsovertuigingen ontstaan zijn weten we niet; ...: maar het is opvallend hoe een geloof dat in de vroege levensjaren voortdurend werd ingeprent, als het brein nog ontvankelijk is, welhaast de status van instinct verwerft; en de essentie van een instinct is dat het wordt gevolgd, zelfs tegen de ratio in.”

“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.”