to each other, it helps to examine why chimps, our closest living relative, cannot learn language.
For chimpanzees, competition is the norm, not cooperation. Mother chimpanzees (and other monkeys) don’t allow anyone else to interact with their babies for about six months. In contrast, human mothers allow others (parents and non-parents, so-called “allomothers”) to interact with a newborn baby immediately after birth. This practice, known as collective breeding, seems to have started with homo erectus, an ancestor who lived about 1.8 million years ago.
Infants raised in collective rearing face two problems. In addition to discerning their mother’s emotions and learning to identify with her, collectively-raised infants encounter the same problem when interacting with alloparents. Therefore, infants raised this way are socially challenged in a way that monkeys are not.
Chimpanzees are not only more competitive than humans, but they rarely share any rewards, such as trading a banana for grapes. Collective breeding changed that and made cooperation, rather than competition, the norm.
Human infants not only exchange physical rewards, but also participate in exchanges where the reward is social, for example, when they inform another person of the location of a missing object by pointing at it.
Infants who have good relationships with alloparents were more likely to survive than those who did not. This selection pressure has helped foster the high degree of cooperation which is crucial for developing intersubjectivity and joint attention.
Intersubjectivity refers to exchanges of affect between an infant and the caregiver that often manifest itself in play. Peek-a-boo, a game observed in all cultures, is a good example. Joint attention refers to a relationship between an infant and caregiver in which they share their attention on external objects, for example, an infant denoting a dog.
Intersubjectivity begins at birth, a consequence of the cradle and proximity of the infant’s eyes to those of his mother. The bond they form is then amplified by the joint attention of an infant and his caregiver to objects of mutual interest.
The dynamics of intersubjectivity and joint attention are invisible to the untrained eye. What greater joy for parents than playing hide and seek with their baby or seeing their baby show something and then smile? Such a game is necessary to produce the child’s first words around his first birthday.
Hyper-cooperation, intersubjectivity, and joint attention have collectively created a perfect storm for the transition from animal communication to words. Linguists have neglected this transition in favor of the passage from words to grammar, the most famous feature of the language. It is easy to show that the transition from animal communication to words required more structural changes than words to grammar, in particular, the transition from analog primate calls to discrete digital speech. But grammar could not evolve without words.
The analog signals that animals use to communicate vary in intensity and frequency. In addition, the average number of signals used by a given species rarely exceeds two dozen. On the other hand, the variations of meaning in the language are conveyed by the choice of discrete words, the upper limit of which is enormous. A reader of this blog knows more than 50,000.
The shift from the analog emotional signals that animals communicate to discrete words has been a dramatic evolutionary change. Besides the nature of the signal, emotional signals also differ fundamentally from words in that they are involuntary, un-learned, and one-way. Their only function is to influence the behavior of others, such as asserting dominance, demarcating a territory, expressing an interest in mating, alerting others to a predator, finding food, etc.
Emotional signals are also immutable. Dogs can only bark, cats can only purr, birds can only sing, and lions can only roar.
Words are voluntary, learned and arbitrary. Typically, words are also conversational. A speaker and a listener alternate roles while shar