In Chapter Seven, Learning and Conditioning, we read about the problems Keller a

Just as a pig’s natural instinct is to root, a person’s natural instinct is to learn language.
Humans are biologically primed to learn language. 
If a child is exposed to language during an early critical period, language will develop.
Language development is also influenced by operant and classical conditioning.
For example, when words and objects are associated with each other, we begin to respond to both in the same way.  Thus, words can acquire meaning as symbols of objects through classical conditioning.
An example of the effects of operant conditioning on language development occurs when a mother first hears her child utter a sound that, to the mother, sounds somewhat like Mama.  She responds with smiles and hugs, reinforcing the child’s utterance.
Shaping also occurs as reinforcements for closer and closer approximations of correct sounds occur.  For example, when a parent correctly guesses that the sound a child utters means “milk” and gives the child milk, the child’s production of that sound is reinforced.  The next time, the sound may be a little closer to the correct sound, and so forth.
Just as a child learns language, a dog cannot because it is not biologically adapted for the learning of language.