...I feel most deeply that the whole subject is too profound for the human intellect. A dog might as well speculate on the mind of Newton.— Let each man hope & believe what he can.—

After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable: from that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision.‎

He who is not content to look, like a savage, at the phenomena of nature as disconnected, cannot any longer believe that man is the work of a separate act of creation ... Man is the co-descendant with other mammals of a common progenitor.

It is interesting to contemplate an entangled bank clothed with many plants of many kinds with birds singing on the bushes, with various insects flitting about and with worms crawling through the damp earth and to reflect that these elaborately constructed forms so different from each other and dependent on each other and so complex a manner have all been produced by laws acting around us.

Music was known and understood before words were spoken.

Sympathy for the lowest animals is one of the noblest virtues with which man is endowed.

So in regard to mental qualities, their transmission is manifest in our dogs, horses and other domestic animals. Besides special tastes and habits, general intelligence, courage, bad and good tempers. etc., are certainly transmitted.