Final answer:
Apes are able to learn sign language due to their biological capacity for basic vocabulary and communication but not vocal language because they lack the specialized vocal tract. Studies like those involving Koko the gorilla offer insights into the cognitive abilities of great apes and suggest a protolanguage might exist among them.
Step-by-step explanation:
Understanding Language Acquisition in Apes
Apes such as chimpanzees, gorillas, bonobos, and orangutans have demonstrated the capability to learn sign language but not vocal language. This is due to their lack of the specialized vocal tract that humans have, which is required for producing the complex sounds of human speech. Instead, these great apes possess the biological capacity to learn and use a basic vocabulary and combine words or signs to achieve communication goals, indicating the potential for a protolanguage among them.
The vocalizations of wild primates, while sometimes intricate, like the gibbons' morning songs or chimpanzees' pant-hoots, do not exhibit the limitless recombination or the expressive capabilities of human language. Primatologists acknowledge that great apes communicate via gestures, facial expressions, and vocalizations, forming a rudimentary communication system, an early form potentially paving the way for human language development.
Research indicates that apes can master basic vocabulary and some even show the ability to invent new signs, as observed in the renowned case of Koko the gorilla, who was taught sign language by Dr. Francine Patterson. Although such studies prove controversial, with some skepticisms about the interpretation of sign utilization, they nonetheless shine light upon the cognitive capabilities of apes and the evolutionary underpinnings of language.