Final answer:
Chimpanzees and gorillas have been taught American Sign Language to communicate with humans, demonstrating a capacity for a protolanguage. The gorilla Koko learned over 1,000 signs and displayed complex communication abilities, challenging our understanding of language development in primates.
Step-by-step explanation:
In controlled conditions, chimpanzees and gorillas such as the famous Koko have been taught to use various forms of American Sign Language (ASL) to communicate with their human handlers. These primates are capable of using signs and gestures to express their wants and comment on their environment, demonstrating a basic capacity for a protolanguage that may precede human language. Koko, raised by Dr. Francine Patterson, learned more than 1,000 signs, similar to the vocabulary level of a three-year-old human child, enabling her to joke, lie, and even teach other gorillas to sign. The complexities of these interactions point to both biological capacities and learned behaviors, underlining challenges to our understanding of language origins and cognitive abilities in non-human primates.