People seem always to have understood that humans are just another kind of animal and not necessarily better than the rest.

Richard Ryder argues that early Christian views created a sense of human-nonhuman separation within the assertion that men and women could not be animals since humans were created in the image of "God" who had given only "their kind" an immortal soul.  Such views explain why a good deal of recent animal rights discourse has sought to challenge this absolute separation and remind human beings that "we" too are animals.  However, even long before Darwin, it appears that there was recognition and acknowledgement that humans were indeed "animals," although "developed" ones.  Ryder, in Animal Revolution, states that "classical literature, Epicureans and writers such as Lucretius, Cicero, Diodorus Siculus and Horace had suggested that humankind had only slowly developed from the animal condition." Aristotle, despite his insistence that humans, animals and nature were held in a “natural hierarchy of value,” never claimed that a human being should not be regarded as an animal.…

Read it all:  http://human-nonhuman.blogspot.com/2010/11/start-with-god.html