Despite sharing a close genetic relationship and remarkable intelligence, apes cannot speak like humans. This difference stems from distinct evolutionary paths shaping human anatomy and neurological capabilities for complex spoken language. While apes communicate effectively within their own species, their physical and cognitive frameworks prevent human-like speech.
The Physical Limitations of Ape Vocal Anatomy
Ape vocal anatomy presents a significant barrier to human-like speech. Unlike humans, apes lack the specific vocal tract structures needed for the wide range of sounds in human speech. The human larynx is positioned lower in the throat, creating a longer pharyngeal cavity. This elongated vocal tract allows the tongue to move freely and shape sounds into distinct vowels and consonants.
Apes also lack the fine motor control over their vocal cords and diaphragm that humans possess. Human vocal cords make precise movements and tension changes, essential for modulating pitch and creating clear, stable sounds. Many primate species, including apes, have vocal membranes and balloon-like air sacs in their larynx. These structures contribute to loud, high-pitched calls but hinder the precise control needed for articulate speech, resulting in noisy, irregular vocalizations.
Brain Structure and the Capacity for Language
The brain’s neural architecture plays a central role in language capacity. Human brains feature specialized areas like Broca’s and Wernicke’s areas, intricately involved in speech production and comprehension. Broca’s area, in the frontal lobe, is primarily responsible for verbal production and articulation planning. Wernicke’s area, in the temporal lobe, is crucial for understanding written and spoken language. These areas are interconnected by neural pathways, notably the arcuate fasciculus, facilitating communication between language production and comprehension centers.
Apes possess brain regions similar to Broca’s and Wernicke’s areas, but these homologous structures are less developed or interconnected for complex symbolic spoken language. The human arcuate fasciculus, for instance, is significantly stronger and more widespread than in non-human primates. Research indicates a specific subregion within the ventrolateral prefrontal cortex (PFOp), fully developed in humans for vocal control, is only partially developed in chimpanzees and absent in Old World monkeys. This suggests a progressive evolutionary development tied to speech. Human language circuits, including those involving subcortical structures like the basal ganglia and cerebellum, are highly specialized for syntax, grammar, and abstract thought, which are not fully present in apes.
How Apes Communicate Without Speech
Apes employ various natural communication methods without human-like speech, demonstrating their intelligence and social complexity. They extensively use body language, including postures and gestures, to convey messages. Specific hand signals in bonobos and chimpanzees, for example, have clear meanings; scientists identified around 70 such signals in bonobo communities. These gestures are often intentional and shared across different ape species.
Facial expressions also serve as a primary means of communicating emotions among apes, with a repertoire similar to humans. Beyond visual cues, apes use various vocalizations like grunts, hoots, and screeches, though their range of distinct sounds is limited compared to human speech. These vocalizations often express immediate emotional states or alert others to danger. While effective for their social and survival needs, these communication systems lack the sophisticated symbolic and grammatical structure characteristic of human language.
What Learning Experiments Reveal About Ape Language
Scientific experiments teaching apes human-like communication provide insights into their cognitive abilities and highlight unique aspects of human language. Early projects, such as those with Washoe the chimpanzee, focused on American Sign Language (ASL). Washoe learned over 350 signs and combined them meaningfully, demonstrating an ability to communicate with humans through gestures. Koko the gorilla learned over 1,000 ASL signs and understood approximately 2,000 spoken words, even inventing new signs.
The bonobo Kanzi, exposed to spoken English and a symbolic system called lexigrams from a young age, showed remarkable comprehension of spoken words and responded to novel commands. Kanzi’s ability to understand novel sentences and some grammatical relationships, like word order, suggests a capacity for symbolic understanding and limited syntax. Despite these achievements, apes in these experiments did not spontaneously develop complex, grammatical spoken language or the intricate syntax seen in human children. These studies indicate that while apes can acquire a substantial vocabulary and exhibit symbolic thought, they do not naturally acquire or produce human-level linguistic complexity.