Language Evolution and Computation Bibliography

Vocalizations are a pervasive feature of nonhuman primate social life, yet we know surprisingly little about their function. We review studies supporting the hypothesis that many primate vocalizations function to facilitate social interactions by reducing uncertainty about the signaler's intentions and likely behavior. Such interactions help to establish and maintain the social bonds that increase reproductive success. Compared with humans, songbirds, and a few other mammals, primates have small vocal repertoires that show little acoustic modification during development. However, their ability to modify call usage is extensive and tuned to variation in the social context, including the historical relationship between caller and listener and the caller's assessment of how a listener is likely to respond. We suggest parallels between the decision to vocalize and neurophysiological studies of other, nonvocal social decisions between interacting monkeys. The selective factors driving the early stages of language evolution may have come from the need to make decisions about when and how to call within the context of social challenges.

The production of vocalizations by monkeys and apes is often described as highly constrained and fundamentally different from human speech. We review recent field studies of baboons and bonobos that suggest greater flexibility. Calls function to reduce the uncertainty inherent in social interactions. Vocal production, like individuals’ responses to calls, is subtly tuned to variation in the social context, including a caller’s assessment of how a listener is likely to respond. We suggest parallels between the decision to vocalize and laboratory, neurophysiological tests of social decisions. We also discuss implications for theories of language evolution.

This article describes the primate social cognition as a precursor to language. The goal of phylogenetic reconstruction is to group similar animals together. One method of phylogenetic reconstruction is based on measures of distance, and arranges species into a phylogeny such that each is grouped with those with which it shares the greatest number of characters. Other methods rely on parsimony, generating the phylogeny that requires the fewest evolutionary changes in character states. Among primates, both methods yield a branching tree structure in which humans are grouped more closely with apes, less closely with Old World monkeys, and progressively less closely with New World monkeys, prosimians, and non-primate mammals. This phylogeny is consistent with both distance and parsimony such as morphological and genetic evidence to indicate both that there is less-evolutionary distance between humans and chimpanzees/bonobos than between humans and any other primate and also that a phylogeny that groups humans and chimpanzees/bonobos together is more parsimonious than a phylogeny that does not. Non-human primates use acoustically different vocalizations in different social contexts, suggesting that the mechanisms underlying call usage have a strong genetic component, although perhaps not as strong as the mechanisms underlying call production. The theory of mind spurred individuals not only to recognize other individuals' goals, intentions, and even knowledge as monkeys and apes already do but also to share their own goals, intentions, and knowledge with others. The evolution of a theory of mind thus spurred the evolution of words, grammar, and the vocal modifiability that these traits required.

Primate vocal communication is very different from human language. Differences are most pronounced in call production. Differences in production have been overemphasized, however, and distracted attention from the information that primates acquire when they hear vocalizations. In perception and cognition, continuities with language are more apparent. We suggest that natural selection has favored nonhuman primates who, upon hearing vocalizations, form mental representations of other individuals, their relationships, and their motives. This social knowledge constitutes a discrete, combinatorial system that shares several features with language. It is probably a general primate characteristic whose appearance pre-dates the evolution of spoken language in our hominid ancestors. The prior evolution of social cognition created individuals who were preadapted to develop language. Several features thought to be unique to language --like discrete combinatorics and the encoding of propositional information-- were not introduced by language. They arose, instead, because understanding social life and predicting others' behavior requires a particular style of thinking.

If we accept the view that language first evolved from the conceptual structure of our pre-linguistic ancestors, several questions arise, including: What kind of structure? Concepts about what? Here we review research on the vocal communication and cognition of nonhuman primates, focusing on results that may be relevant to the earliest stages of language evolution. From these data we conclude, first, that nonhuman primates' inability to represent the mental states of others makes their communication fundamentally different from human language. Second, while nonhuman primates' production of vocalizations is highly constrained, their ability to extract complex information from sounds is not. Upon hearing vocalizations, listeners acquire information about their social companions that is referential, discretely coded, hierarchically structured, rule-governed, and propositional. We therefore suggest that, in the earliest stages of language evolution, communication had a formal structure that grew out of its speakers' knowledge of social relations.

Cheney and Seyfarth enter the minds of vervet monkeys and other primates to explore the nature of primate intelligence and the evolution of cognition.

TABLE OF CONTENTS
1. What Is It Like to be a Monkey?
2. Social Behavior
3. Social Knowledge
4. Vocal Communication
5. What the Vocalizations of Monkeys Mean
6. Summarizing the Mental Representations of Vocalizations and Social Relationships
7. Deception
8. Attribution
9. Social and Nonsocial Intelligence
10. How Monkeys See the World