I recommend a new reader turn to the chapter on the first year of infancy. Most people who spend time with infants (including their parents) think they are just playing and having fun. That's of course true but virtually no one appreciates the structure and function of that play and how it inexorably leads to language.Peter Hobson, a British psychoanalyst, has provided the best description I know of regarding the path to language: "Those psychologists who believe that humankind became unique by acquiring language are not altogether wrong. But they are not altogether right, either. Before language, there was something else more basic, in a way more primitive, and with unequalled power in its formative potential that propelled us into language. Something that could evolve in tiny steps, but suddenly gave rise to the thinking processes that revolutionized mental life. (...) That something else was social engagement with each other. The links that can join one person’s mind with the mind of someone else—especially, to begin with, emotional links—are the very links that draw us into thought."Those links begin with the practice of cradling and the opportunities cradling provides for social engagement. Among primates, only humans cradle their infants because new-born infants are the least developed. The volume of an infant’s brain is approximately 25 percent of its adult size; in chimpanzees, it’s 45 percent. Similarly, the human skeletal system is poorly developed. As a result, an infant cannot locomote and must be cradled for six months.An important benefit of cradling is the proximity of the infant’s and parent’s eyes, allowing them to share each other’s affect and gaze, one of many quirks of evolution that laid the groundwork for language. In compensation, as it were, for the infant’s lack of mobility, infant and parent can observe and anticipate each other’s behavior to an amazing degree during cradling. How many times have you heard, and likely said yourself, when watching a baby in their parent’s arms, look at how the baby’s eyes are soaking up knowledge-– or words to that effect? Look how she watches other people. She’s like a sponge.Developmental psychologists have shown that those interactions are rhythmic. Parent and infant take turns in expressing affect and in engaging in non-verbal auditory behavior (whimpering, gurgling, and so on). An important feature of those interactions is that they are conversational. After a mother smiles, raises her eyebrows, makes a sound, shakes her hands, and so on, so does the infant. Long before an infant utters her first words, she's engaging in proto-conversations of affect with her mother and others.While playing with an infant, it is commonplace for a parent to engage the infant’s interest in an object by looking at that object, waiting for the infant to gaze at it, and then look back at them and smile. Such examples of joint attention provide the first instance in which an infant and another person share the contents of their minds, in this example, knowing that each one saw a particular object.There are two major implications I would like the reader to draw from my book. The first is the importance of non-verbal experiences that an infant shares with their parents. The other is how to overcome the weakness of Chomsky's theory of the evolution of language.Now that intersubjectivity and joint attention have been well documented by developmental psychologists, we need to learn more about their antecedents. For example, the renowned anthropologist Sarah Hrdy, has suggested that Homo erectus benefited from cooperation instilled by collective breeding, the practice of sharing the care of infants with relatives. Unlike a chimpanzee mother, who won't allow anyone to approach a newborn infant for six months, there is evidence that Homo erectus’ infants were raised by "alloparents" in addition to their own mothers. Satisfying alloparents is presumed to strengthen intersubjectivity which, in turn, facilitates cooperation.Recent advances in technology allow researchers to detect the focus of attention of a parent and their infant over long intervals of time. Such data will, for the first time, allow investigators to measure joint attention precisely in a variety of situations.Chomsky's prominence as a linguist is based on his concept of a Universal Grammar that can generate any of the languages that people speak. Those models have transformed linguistics and have contributed significantly to cognitive psychology. Chomsky’s anti-behaviorist stance has served him well in developing models of grammar. The same cannot be said for his treatment of words. Although Chomsky believes that grammar is innate and that it resulted from a mutation, the same cannot be said of words. Words have obvious behavioral origins, origins that are clearly social. The challenge is to determine those origins. If I were starting out as a graduate student and needed a field of inquiry to study, that would be my focus.Given our current technological sophistication, I anticipate important discoveries about how language not only began but how it has also thrived. Words provide the glue that allows for and preserves learning, intelligence, knowledge, invention, discovery, understanding, wisdom, and love.