Developmental and Evolutionary Origins of Language: Insights from the Study of Pointing and Gaze in Infants, Bonobos, and Chimpanzees

The uniquely human ability to acquire language has led to two important and enduring questions: how did humans evolve the ability to communicate through language, and how do human infants acquire this ability so adeptly? Here, I aim to provide new insights into these long-standing questions by exploring how human infants and nonhuman primates use and develop nonverbal communicative behaviors.

Chapter 1 introduces the significance of the empirical studies by outlining the role of nonverbal behaviors in shaping uniquely human communicative skills, along both evolutionary and developmental timelines. In Chapter 2, I take a developmental approach and investigate the role of one particularly important nonverbal behavior, infants’ pointing gestures, in facilitating early language development. I found that pointing has a direct and immediate impact on word learning: in the moment an infant points toward an object, they have a heightened readiness to learn that object’s label. In Chapter 3, I test how pointing relates to learning in a variety of domains, and explores potential motives driving infants’ production of pointing. Results demonstrated that pointing reflects a heightened readiness to learn both labels and functions, and are potentially motivated by requests for objects’ labels. In Chapter 4, I take an evolutionary approach and describe a study assessing another important form of nonverbal communication, gaze alternations, in bonobos and chimpanzees. Like humans, bonobos and chimpanzees gaze alternated more when interacting with an attentive, as opposed to inattentive, communicative partner. However, unlike humans, individuals produced few gaze alternations (bonobos) or only frequently gaze alternated after reaching adulthood (chimpanzees).

Chapter 5 provides an overview and synthesis of the empirical findings, as well as important future directions. Together, the studies presented here confirm that nonverbal behaviors are a critical feature of the communication systems of both nonhuman apes and human infants. By demonstrating how human infants and nonhuman apes use nonverbal behaviors to communicate and learn, the current findings provide unique insights into the origins and development of language.