Dr. Valerie Chalcraft, Research Associate at the Gorilla Foundation, presented this talk at a workshop entitled Gestural Communication in Nonhuman and Human Primates held March 28-30, 2004 at the Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany.

According to the Max Planck institute, the workshop was "...organized with the goal to present a variety of approaches and methodologies used in different fields of research concerning gestural communication and to discuss those issues in the background of the conference Evolution of Language. With respect to the theory of a gestural origin of language it is of great importance to investigate if and to what extent gestural communicative systems can be compared between and within different species of primates, including humans."

Dr. Chalcraft's presentation, "Sign Modulations of Cross-Fostered Chimpanzees and Gorillas," demonstrated that both chimpanzees and gorillas (Koko) who have been taught American Sign Language (ASL) modulate their sign to change the meaning or emphasis in a manner similar to human signers:

The part of the study involving chimpanzees was performed by Dr. Chalcraft as part of her Ph.D. dissertation before coming to the Gorilla Foundation. The part of the study involving a gorilla was extracted from the video records of Project Koko. The chimpanzee study analyzed video records of one chimpanzee cross-fostered by humans in a human environment and exposed to American Sign Language (ASL). Video examples and video data analysis showed that, like human signers, the chimpanzee modulated verbs and noun/verbs to indicate actor, instrument, and location. Video examples and video data analysis also showed that, like human signers, the chimpanzee modulated all types of signs to indicate intensity. Many of the same modulations appear in the video records of Koko and examples were presented.

The photo above shows Koko signing “tickle” on her foot after Dr. Patterson signs “Where do you want me to tickle you?” Just like human signers, Koko incorporates the location “there” (one her foot) in her sign “tickle.”

These observations of sign language modulation in both chimpanzees and gorillas show the continuity of sign language development across species and provide implications for the evolution of language.

Valerie Chalcraft, Ph.D.
Research Associate
Gorilla Foundation / Koko.org

Note: The complete set of multi-media slides used in Dr. Chalcraft's Powerpoint Presentation will be made available on this website. If you would like to be notified by email, just sign up for KokoMail.