Introduction

Humans have the ability to effortlessly acquire thousands of words, which are each associated with a wide range of semantic references. Other species share this ability to a limited degree. Chimpanzees who have acquired the ability to communicate by means of manual sign language or other manual systems have 150 word productive vocabularies and can coin new words. They appear to think in terms of words, signing the names of objects as they look at picture-books (Gardner and Gardner 1980). Chimpanzees, both “common” (Gardner and Gardner 1980) and bonobos (Savage-Rumbaugh et al. 1986) can comprehend distinctions in meaning conveyed by the syntax of simple sentences and aspects of the morphology of ASL. Although present-day chimpanzees are not identical to the common ancestor of humans and apes who lived some six or seven million years ago, they in many ways are living hominoid fossils and any capacity present in chimpanzees most likely was present in our common ancestor. Likewise, any aspect of human linguistic ability that is absent in chimpanzees is a “derived” feature that evolved in the course of human evolution.

The derived properties of language that will be discussed here are speech and syntax. Chimpanzees cannot talk, although they could form many of the phonetic distinctions that convey human language (Lieberman 1968). Non-human primates lack the neural capacity that allows humans to produce a potentially limitless number of words from a finite set of motor gestures.