Final answer:
Nonhuman primates and other animals are unable to use human speech due to anatomical limitations, lack of necessary neural networks, and differences in brain structure. While some primates can use symbolic gestures, they do not possess the required elements for complex, open-ended language. This ability for varied and infinite language appears unique to humans and is tied to our vocal tract anatomy and specialized brain functions.
Step-by-step explanation:
Primates and other animals cannot use human speech primarily because of differences in vocal tract anatomy, brain structure, and the neurological foundation complex speech requires. The human vocal tract allows for the varied production of sounds through the controlled movement of the larynx, tongue, and lips, a feature not present in primates. In addition, while some primates are capable of learning basic signs or gestures that approach the foundational aspects of language, known as protolanguage, they lack the neural networks necessary to produce or comprehend the open-ended and infinitely combinable elements of human language.
Research into the abilities of primates, like Koko the gorilla, indicates that they have some capacity for using symbols and can comprehend a limited set of signs or gestures in a rule-based way. However, this is a far cry from the flexible use of language seen in humans. The mirror neuron system, which allows primates to recognize and imitate actions, provides some insights into the evolutionary building blocks of language. It is hypothesized that initial forms of human language could have evolved from a system of gestures.
Philip Lieberman's research into Neanderthal anatomy suggests that even our close evolutionary relatives lacked the physical apparatus for human-like speech. The ability to produce complex language probably emerged relatively late in human evolution, providing our species with significant advantages in communication and social organization.