Combinatoriality in the evolution of human language
What is the question to ask about the evolution of human language? We know for certain that there is no way to reconstruct an original language or protolanguage by tracing contemporary languages back in time. There have been a number of proposals about how human language originated. Here we focus on how language came to have the form it has, concentrating on phonology, the combinatorial system that combines meaningless speech sounds into meaningful words. While the earliest stages of the phonologies of spoken languages evolved too long ago to be reconstructed, we can learn much from the sign languages that have evolved much more recently among deaf people and in communities with a significant deaf population. The key concept is the contrast between gestures and signs. While gestures vary in all kinds of ways, Stokoe (1960) showed that the signs of American Sign Language (ASL) consist of smaller parts (handshape, movement, and location) that combine to yield different signs. Like spoken languages, ASL and other mature sign languages have combinatorial phonological systems. With a relatively small inventory of handshapes, movements, and locations, many different combinations are possible, yielding a large number of signs. Do sign languages have combinatorial phonological systems from the outset? Sandler et al. (2011) studied a newly developing sign language used by deaf and many hearing people in a Bedouin community in the Negev desert in southern Israel. They argue convincingly that it does not have a combinatorial phonological system like mature sign languages. These Bedouins communicate with gestures, not combinatorial signs. This is evidence of the viability of gestures for communication, at least in a small community whose members all know each other and share knowledge of their surroundings. New sign languages may begin as such gestural systems, evolving into sign language over time. What would cause a gestural system to evolve into a sign language? First a combinatorial phonology yields more consistent and uniform articulation in the community, facilitating comprehension of others’ signing. With gestures, nothing would constrain variation and hence difficulty understanding others. Second, combinatorial phonology makes possible a vast expansion of the vocabulary. The relation between a sign’s meaning and its form can be arbitrary, like the relation between words’ sounds and their meanings in spoken languages. This enables combinatorial sign languages to have signs for any meaning. These two advantages of combinatorial sign languages like ASL over gestural communication are precisely what did not result from attempts to teach ASL to chimpanzees. First, the chimpanzees’ “signing” was judges by ASL signers to be “erratic” – as opposed to the more consistent and relatively uniform signing of human signers. This is explained if the chimpanzees had not learned ASL’s combinatorial phonology that shapes human signing. Second, while a combinatorial phonology makes possible a vast increase in the size of the vocabulary, the chimpanzees’ vocabulary was tiny. This is explained if they had not learned any signs at all, but only a small number of gestures. We conclude that chimpanzees do not have the combinatorial abilities needed to learn a human language. Phonology is only one of several combinatorial systems in human language. Morphology combines meaningful parts of words into complex words, syntax combines words into phrases and phrases into sentences, semantics combines word meanings into the meanings of phrases and sentences. All take advantage of humans’ combinatorial abilities. Chimpanzees’ failure to master ASL phonology is due, we claim, to their not having those abilities. It is our combinatorial abilities that make human language possible. We are a combinatorial species.