Human uses of mammals that "one is well advised to study the behaviour rather than attempting to get at any underlying emotion". Charles Darwin however had accepted the idea of emotion in animals, writing his 1872 book "The Expression of the Emotions in Man and Animals" on the subject. Darwin believed that mammals had social, mental and moral lives. In "The Descent of Man" (1871), he wrote: "There is no fundamental difference between man and the higher mammals in their mental faculties." Biologists remained wary of the idea, even for the great apes, but this led to serious difficulties, as Donald O. Hebb explained
Catholic theology of the body positive image of man by stating his freedom and independence. God is truly free and the freedom of man, even if limited, is an image of God. Not only his freedom, but also his ability to love - God is love - and his immortality, make man an image of God. Regarding the human body, Gregory opines that it is created for procreation. In that, humans are like animals; however, the human body also has the capacity for reasoning and perception. The body has three forms of life: the vegetative, sensual and intellectual. The human body derives its dignity from