Compared to equally sized wolves, dogs tend to have 20% smaller skulls, 30% smaller brains^[103], as well as proportionately smaller teeth than other canid species.^[104] Dogs require fewer calories to function than wolves. Their diet of human refuse in antiquity made the large brains and jaw muscles needed for hunting unnecessary. It is thought by certain experts that the dog's limp ears are a result of atrophy of the jaw muscles.^[104] The skin of domestic dogs tends to be thicker than