"There is no fundamental difference between man and the higher mammals in their mental faculties ... The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind. The love for all living creatures is the most noble attribute of man. We have seen that the senses and intuitions, the various emotions and faculties, such as love, memory, attention and curiosity, imitation, reason, etc., of which man boasts, may be found in an incipient, or even sometimes a well-developed condition, in the lower animals."
Charles Darwin (1809-1882), English biologist and naturalist, The Descent of Man