why do we maintain human speech as superior? According to Fudge (2002):


Descartes argued that language was evidence of reason, and because animals could not speak it is proved 'not merely that the beasts have less reason than men, but that they have no reason at all' [1637]. Not noise, not the ability to communicate, but the ability to communicate through language is what distinguishes human from animal. With this powerful philosophical argument in mind, experiments on the possibility of animals learning to communicate with humans through different types of language – sign language, symbolic language – were clearly looking not only at animal capability, but also at the border between animals and humans. If a chimpanzee can be said to 'speak' using his hands, where does the difference between the species lie? Where is our power then? (p. 118)