Biological anthropologists posit that we share a common ancestor with the other great apes (gorillas, chimpanzees, bonobos, and orangutans) about five to eight million years ago. As nonhuman primates do not produce language in the wild, the biological and cultural features that promoted language must have emerged after that. However, studies aimed at teaching human language to nonhuman primates have revealed that individuals of these species are able to master basic vocabulary and use simple words and word combinations to obtain the things they want. So the great apes must have some biological features that enable them to learn human language in a partial and limited way. You may have heard of Koko, the gorilla famous for learning to use sign language. Sign language is used in such studies because nonhuman primates lack the distinctive vocal tract required to make the sounds of human language. Researcher Penny Patterson taught Koko to use about a thousand signs, roughly the vocabulary of a three-year-old child (Patterson and Linden 1981). Patterson reported that Koko could comment on things that were not currently present in her environment, such as personal memories. According to Patterson, Koko could joke and lie and teach other gorillas to sign. She could even invent new signs. Many of these claims are disputed by other researchers. Some point out that the evidence is largely anecdotal and relies on the interpretation of Patterson herself, hardly an objective observer. Though controversial, Patterson’s path-breaking work with Koko provided a wealth of data and opened up new possibilities for understanding the language abilities of nonhuman primates. Figure 6.5 Koko learning to play the guitar. Koko became famous for learning to communicate with humans using roughly 1,000 signs taught to her by researcher Penny Patterson. (credit: “ODCnewBegin9” by FolsomNatural/flickr, CC BY 2.0) Human-reared chimps, gorillas, bonobos, and orangutans have all been taught to use gestures or tokens to refer to things in the world around them, often combining those signs in a rule-based way to make comments and requests. Even though many linguists are skeptical of these studies, the use of symbolic systems in cooperative interactions to achieve goals does seem to indicate that great apes have the basic capacity to generate some sort of protolanguage. Protolanguage refers to a very simple set of gestures or utterances that may have preceded the development of human language. But do apes display these abilities due to some innate capacity or because we have taught them symbolic systems? Perhaps learning a symbolic system has changed the brains of these individual animals in distinctive ways. Figure 6.6 Chimpanzees use gestures and facial expressions as well as vocalizations to communicate with one another. (credit: “Chimpanzees” by foshie/flickr, CC BY 2.0) Many primatologists conduct research on the vocal and gestural forms of communication used by primates in the wild, looking for those biological features that might underpin the human capacity for language. Wild chimpanzees, for instance, produce a wide range of calls, including hoots, pant-hoots, pant-grunts, pant-barks, rough-grunts, nest-grunts, alarm barks, waa-barks, wraas, screams, and soft panting play sounds (Acoustical Society of America 2018). Primatologists have listened closely to these calls. Some argue that chimp vocalizations are not much like human language, as calls are fairly fixed and limited in their meanings. Chimps may use a rough grunt to indicate a food source, but they do not seem to have specific grunts for specific food types. Monogamous pairs of gibbons, a smaller species of ape, are known to perform elaborate morning duets. Gibbons have an array of predator calls as well. Research comparing duets with predator calls suggests that gibbons compose their songs to convey specific information, each note carrying a certain meaning (Clark et al. 2006). While impressive, the ability to manipulate notes to convey a limited range of meanings is still a far cry from the infinite productivity of human language. The limitless recombination of signs that produces the flexible, open-ended quality of language is missing in the communication systems of wild primates.