Final answer:
Captive bonobos, like Kanzi and Panbanisha, show language comprehension abilities akin to a human child, successfully using lexigrams to communicate. Other apes have also learned to use signs or symbols, exhibiting basic language skills. The fundamental difference is the lack of infinite recombination of signs, making their communication systems less complex than human language.
Step-by-step explanation:
Captive bonobos show language comprehension abilities similar to that of a human child. Studies by Sue Savage-Rumbaugh demonstrated that bonobos like Kanzi and Panbanisha could use a computer-based language program with lexigrams to respond to human speech and generate language, exhibiting cognitive linguistic skills. Despite not having the vocal apparatus to speak, these bonobos were able to understand and communicate at a remarkable level, as seen with Kanzi scoring higher in a language competence study than a two-year-old human child.
Promising results also come from studies involving other great apes like chimpanzees, gorillas, orangutans, and notably, the gorilla named Koko, who learned sign language. These studies suggest that primates can learn basic vocabulary and use simple words and word combinations to communicate their desires. Although the great apes don't have the ability to produce language in the wild, they possess certain biological features which enable them to learn human language to a certain extent when taught.
However, it's important to note that the communication systems of nonhuman primates do not exhibit the open-ended, flexible structure of human language. Protolanguages used by these animals often show rule-based construction but lack the infinite recombination of signs found in human language. This indicates a fundamental difference between the communication systems in humans and those in our closest primate relatives.