He begins by quoting science writer Tom Seigfried who states that: It’s true that humans, and humans alone, evolved the complex set of voice, hearing and brain-processing skills enabling full-scale sophisticated vocal communication. Yet animals can make complicated sounds; parrots can mimic human speech and cats can clearly convey that it’s time for a treat.
Many animals possess an acute sense of hearing and are able to distinguish random noises from intentional communication.
Much of the physiological apparatus for hearing and speaking is found in all land-dwelling vertebrates — the tetrapods — including mammals, birds, amphibians and reptiles. “Humans share a significant proportion of our basic machinery of hearing and vocal production with other tetrapods,” Fitch writes in the Annual Review of Linguistics. Even so, only humans have language, Egnor argues. Here's part of his reasoning:
[Animals] can make and respond to signs—gestures, grunts and the like. A dog, for example, can respond appropriately to simple words directed at him (“Sit!” “Fetch!”). But all animal communication is symbols, that is, signals that point directly to an object. In this case, the object is a simple expected action the animal is to perform immediately.Language is a tool for abstract thinking and only human beings can do that. The gap between animals and human beings is not just a narrow evolutionary jump. It's a chasm.
What animals cannot do is communicate using abstractions. They cannot use designators, — words employed abstractly as language. For example, a dog can be trained, by reward and punishment, to stay when told, “Stay!”
He associates the sound “s-t-a-y” with a behavior and performs the behavior. But he doesn’t know what you mean when you say “Let’s stay a bit longer on the beach,” “He extended his stay in Peru,” or “The judge issued a stay of the eviction order.”
Animals can only think concretely. Their thought is of particulars—the particular bowl of food, thrown stick, or warm bed. They don’t contemplate nutrition, exercise, or rest. Humans can think abstractly, without any particular physical object in mind. For example, a vet might tell her client during an office visit, “Tuffy here needs to lose about 1.5 kg. I suggest a lower calorie kibble and more exercise—if possible, before bedtime.”
She can explain it to her client but not to the dog because it’s all abstractions about times, places, things, and concepts. Of course, he might recognize his name, “Tuffy,” and raise his ears slightly to see if he is being told to do something concrete.
Concrete thought needs no language because the concrete thinker focuses on a perceived object. Tuffy thinks of his bowl of food. If he were to think of nutrition, an abstract concept, he would need abstract designators as objects, not only to express his thought but even to think it.
In short, animals don’t have language because they don’t have abstract thought and thus have neither the capacity nor the need for abstract designators—words as language.