Tickle me Nim. Do primates speak language?

Interspecies communication could be a powerful means of studying the roots and evolution of human language. ALR (ape language research) has been instrumental in this pursuit. Apes are unable to produce spoken words (comparable to human speech) due to anatomical differences. Humans have a smaller tongue and the vocal cords are located lower in the vocal tract, giving humans a greater ability to modulate sounds.

In 1979, a paper was published on a male chimpanzee (Pan troglodytes) named Neam Chimpsky (Nim). Nim was raised in a human environment and was communicated with through ASL from the age of 2 weeks. He was taught ASL with a strategy of observation and hand modeling. When the correct sign was given, Nim was rewarded with either the requested object, action, or some other reward. Unlike previous ALR studies, multi-sign combinations such as more tickle and tickle more were reported as more tickle, since they contained the same information and order did not increase the amount of information contained.

When Nim’s multi-sign combinations were compared to children’s utterances at similar ages, the MLU (mean length of utterance) was similar at 26 months, but Nim’s MLU did not increase, while the children’s MLU continued to increase. Nim displays word ordering rules concurrent with those exhibited by a two-and-a half-year-old child, but is unable to create sentences with the complexity of a typical developmentally normal four-year-old. Table 1 contains Nim’s most frequent two, three, and four word combinations. Since Nim, ALR has continued to refine data collection and explore different methodologies. Some of the most promising work has been completed with a bonobo chimpanzee (Pan paniscus) named Kanzi.

Table 1: A listing of the most frequent sign combinations used by Nim. FQ = Frequency of utterances out of more than 2700 combinations.