Final answer:
Studies have shown that apes can learn to use symbolic systems like gestures or tokens to communicate. These studies indicate that apes have the basic ability for protolanguage, a precursor to human language.
Step-by-step explanation:
Studies into apes learning languages have revealed that great apes, such as chimpanzees, gorillas, bonobos, and orangutans, can be taught to use symbolic systems like gestures or tokens to refer to objects and make comments and requests. Researchers have used methods such as teaching sign language or using computer-based language programs with symbol representations to study apes' linguistic abilities. While some skeptics question the validity of these studies, the use of symbolic systems suggests that apes have the basic capacity for protolanguage, a simple set of gestures or utterances that predates human language development.