"I have just finished my 'Origin,' and am now going to be a hermit for the rest of my life."

"He who understands baboon would do more towards metaphysics than Locke."

"What a book a Devil's Chaplain might write on the clumsy, wasteful, blundering, low, and horridly cruel works of nature!"

"The love of experiment and the patient observation of nature are the two great qualifications for a naturalist."

"There is no fundamental difference between man and the higher mammals in their mental faculties."