For more than 150 years, the assumption that language is a singular event has hampered progress in explaining its evolution. Another obstacle was the inability to recognize that certain social interactions, uniquely human, are necessary for the evolution of language.
These problems have recently been addressed by recognizing that words need to evolve before grammar and by uncovering the nonverbal emotional and cognitive relationships between an infant and the caregiver. As I explain below, these relationships are known as intersubjectivity and joint attention.
Source: Julia Margaret Cameron / Wikipedia
Darwin argued that the theory of evolution could explain the transition from animal communication to language by the principle of natural selection. The idea was that “language differed in degree and not in kind” from animal communication. It remains to discover the degree – “the innumerable gradations” which separate them.
Some of these gradations have been discovered in recent years. But their nature suggests that language differs in nature from animal communication. Along with Darwin, Alfred Wallace, who published the first article on the theory of natural selection, wondered how natural selection, which assumes the survival value of a new ability, could account for “higher intelligence. Of the man. Compared to apes, Wallace couldn’t understand why natural selection would produce anything other than a slight increase in mental capacity. Language, let alone digital literacy or music, is hardly necessary for survival.
Because Wallace assumed language was a singular event, he didn’t realize that words had to evolve before grammar. If he had, he might have recognized how consistent a theory of the evolution of words would be with the principle of natural selection.
Before words could evolve, some of our ancestors had to become more cooperative than the apes. This increased cooperation was necessary for intersubjectivity and joint attention to evolve. To see how the verbal and nonverbal components of language relate 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 fo