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

I believe that animals have descended from at most only four or five progenitors, and plants from an equal or lesser number.

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.

The young and the old of widely different races, both with man and animals, express the same state of mind by the same movements.

In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.

I do not believe, as we shall presently see, that all our dogs have descended from any one wild species; but, in the case of some other domestic races, there is presumptive, or even strong, evidence in favour of this view.