Chimpanzee Gesture Repertoire

Wild chimpanzees use a repertoire of ~66 distinct gestural signals (Hobaiter & Byrne 2014), each with a specific meaning that receivers understand and act upon. The gestures are intentional — produced with apparent goal-directedness, modified when the receiver doesn't respond, and flexibly deployed across contexts. About 30 of these gestures are shared with bonobos, suggesting the repertoire predates the Pan split ~2 million years ago. Some are shared with humans, raising the question of what communicative substrate we inherited.

What the Signals Are

Chimpanzee gestures are body movements directed at a specific receiver — arm raises, object shakes, touches, posture displays. The system the Wikipedia article describes covers the full communicative suite, which also includes:

Facial expressions:

• Full closed grin (fear — contagious; causes nearby individuals to become fearful)
• Open-mouthed grin (playful)
• Pout (distress/begging)
• Sneer (threat/fear)
• Compressed-lips face (display)

Postural signals:

• Bipedal swagger with waving arms (aggression — size exaggeration)
• Crouch/bob/extended hand (submission)

Tactile/percussion:

• Tree drumming — hands and feet on large trunks to communicate location when traveling; also for intergroup encounters

Vocalization:

• Pant-hoot (4-phase: soft hoos → build-up → climax screams/barks → soft hoos): signals social rank and group cohesion; audible at long range
• Grunts: feeding and greeting contexts
• Pant-grunts: submission signal toward dominant individuals
• Short barks: hunting contexts
• Tonal barks: snake-sighting alarm (predator-specific — categorical)
• Distance calls: food, danger, or other group members

The Gesture Repertoire Specifically

Catherine Hobaiter and Richard Byrne's 2014 study (Bossou, Budongo) documented 66 gesture types in wild chimpanzees, each mappable to a specific meaning or small set of meanings. Key findings:

• The system is meaningful — receivers respond appropriately to each gesture, and senders repeat or modify signals when receivers fail to respond (evidence of intentionality and goal-tracking)
• The meanings are consistent across populations — gestures mean the same things in different communities, suggesting the repertoire is species-typical rather than locally learned
• The gestures are not iconic — most don't visually resemble what they mean; they are arbitrary signals, the closest animal parallel to symbolic reference outside of trained language studies
• ~36 of the 66 overlap with bonobo gestures; a smaller subset may overlap with human gesture

Transmission: Innate or Learned?

Marked innate because the cross-population consistency implies the gestures are species-typical — individual chimpanzees produce the same gestures in the same contexts without having learned them from a specific teacher. This is distinct from the Washoe/Nim ASL sign-language experiments, which involved explicitly taught human symbols.

The species-typical gesture repertoire is better compared to the vervet-monkey-alarm-calls than to the ASL studies — it is a natural, population-wide system. The cultural transmission entry for chimpanzees would be their tool-use traditions (nut-cracking, ant-dipping techniques that vary by population) rather than the gesture repertoire itself.

The Sign Language Experiments

Washoe (Gardner & Gardner, 1960s) acquired ~150 ASL signs and spontaneously taught some to her adopted son Loulis. Nim Chimpsky (Terrace, Columbia) appeared to acquire signs but Herbert Terrace later reversed his interpretation: Nim's sequences did not show syntactic ordering, sentences didn't grow in complexity, and Nim rarely initiated exchanges — the behavior could be explained by prompting and imitation.

The honest position: chimpanzees can learn arbitrary symbols for objects and actions, can combine them in limited ways, but the evidence for anything resembling human grammatical syntax is weak.

Open Questions

• What is the mechanism that produces cross-population consistency — is there a genetic predisposition for specific gesture-meaning mappings?
• Do chimpanzees understand the *relationship* between a gesture and its meaning, or respond via learned association?
• The overlap with human gesture has been used to argue that gesture may be the communicative substrate from which human language evolved — this "gesture-first" hypothesis is contested
• Bonobo (*Pan paniscus*) gesture repertoire shows strong overlap; combining the two datasets suggests ~40 gestures are homologous to our common ancestor