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The phenomenon of language is not unique to humans. To some degree, vocal communication is developed in many species. However, the complexity and the variety of human language far supersedes that of even the most developed and complex animals. The reasons for this, as well as the most common prerequisites, are debatable. Most of the scholars ascribe the language to the intricate social structures unique to humans and the inevitability of the emergence of the sophisticated signal system to support the society.
Others point to the evolutionary nature of the phenomenon, citing the evident benefits of the communication means both for the existing socialized species and the purported advantages that were attained by human ancestors as the language developed. In any case, the comparing and contrasting of the vocal communications in humans and non-human primates is the most promising direction for inquiry, as it sheds the most light on the processes that have shaped the language system of humanity.
Production mechanism (anatomy and physiology)
The most influential early approach to the research of human vocal communications was the publication of Darwin’s On the Origin of Species. It allowed viewing the language as a developed trait. The next question was “How did it develop?” This part of the research is complicated by two factors. First, the vocal apparatus is made primarily of the soft tissue, which does not fossilize. Second, the spoken language leaves little to no trace in proto-human culture. Thus, the two main means of tracking are unavailable. The best alternative is to review the tendencies in vocal communications of the nearest species – in our case, primates – and extrapolate the conclusions from the results.
Acoustic structure and degree of complexity
Anatomically, the structure of the vocal apparatus is similar throughout the order of primates, including humans. The crucial components are the larynx, the oral and nasal cavities, also known as “filters”, and the secondary obstacles, like the lips, teeth, and tongue (Ghazanfar and Rendall 457). The basic mechanism for all primates can be described as follows: the air from the lungs goes through the larynx, encounters the vocal cords, which resonate and produce sound. The sound is then further modified by passing through obstacles. Thus, we can say that the mechanism of sound formation is identical in humans and nonhuman primates.
The same can be said about the presence of components crucial for the formation. What sets us apart is the configuration of the equipment. The humans have their larynx sufficiently lowered compared to other species, creating a deeper throat, or pharynx. The oral cavity is also significantly shorter. As the oral cavity serves as a resonant chamber for the modification of vowels produced by the vibrating vocal cords, this change allows for easier manipulation and thus a wider range of sounds. The introduction of the pharynx also contributes to this, essentially creating the second chamber of different qualities.
Furthermore, the velum, which is responsible for separating the nasal cavity, can be locked with epiglottis in non-human primates, limiting their articulation capability. Finally, the primates’ tongue and lips, while well-suited for their primary functions, are underdeveloped for sound modulation. As a result, the acoustic structure of the humans is far more advanced, with the cross-sectional area and length of the pharynx allowing the wide range of correlation of the fundamental frequencies created by resonating of the vocal cords, and the selective frequency suppression properties of the oral and nasal cavities. Both factors contribute to the voice timbre, which, alongside the voice pitch, is often named the main means of conveying a message (Ghazanfar and Rendall 457).
Range of meanings conveyed by the signals
As a result of the relatively simpler vocal apparatus and the resulting narrow range of acoustic variety, we can assume scarcity of the meanings that can be produced via the vocal constructions of the non-human primates. Besides, the sounds articulated by primates are audibly more primitive compared to the much more complex morphemes used by humans. While a morpheme like a word can carry a very specific and defined meaning, which naturally requires a large amount of them to be utilized in a language, signals used by primates only denote general feelings or concepts, like “anger,” “danger,” or “attraction.”
This aligns well with the limitations of their vocal capabilities. However, the research by Seyfarth, Cheney, and Marler discovered an unexpected depth in the range of meanings such signals can convey. The researchers have recorded several types of alarm signals produced by vervet monkeys as a response to the approaching predator or a hazardous animal. Three types of signals were recorded, corresponding to leopard, martial eagles, and snakes.
The initial assumption was that the monkeys were receiving the generalized alarm signal, looked for additional clues to act upon (identified the type of danger visually), and then reacted accordingly. However, the playback of each of the signals has produced the required reaction (reaching for higher ground for “leopard” signal or descending for “eagle” signal) without the actual predator in sight. Additionally, the amplitude modulations applied to recordings showed little change in the response (Seyfarth, Cheney, and Marler 803), which puts the acoustic structure a defining comprehension method.
Social environments of non-human primates
The primary reason for such a complex signal structure is grounded in the complex social structures characteristic for primates. The behavioral models exhibited by them famously include compassion and cooperation.
In some cases, vocal signals play a crucial part in the latter, as shown by the research of the “food calls.” (Hauser 12137) The monkey who has found food is required to announce the finding to the others. The same research has confirmed the tendency of withholding information from the rest of the group for personal gain (basically, a form of cheating) and revealed the raised levels of aggression exhibited towards the cheaters (Hauser 12138). To handle such a sophisticated social structure, the complex signal system, comparable to the rudimentary form of the human language, is necessary (Pearce 327).
Intentionality in the use of vocal signals
The same research also gave insight into the intentionality of the use of vocal signals. It was initially assumed that monkeys tend to adhere to a certain behavior, with the strict division into cheaters and non-cheaters. However, it was discovered that almost every member of the group has withheld information at least once (Hauser 12139). This means that they decide to announce the food finding or be silent depending on the situation (e.g. the proximity to the group and the odds of being discovered). This, again, puts them on a level comparable only to that of humans.
To conclude, the vocal structures used by non-human primates are sufficiently simpler than those used by humans primarily because of the anatomical construction of the vocal apparatus. Despite these limitations, non-human primates make use of the available range of acoustic signals in a conscious way. Their messages are intentional, recognizable, and diverse enough to account for the majority of phenomena relevant to their environment and social structure. Thus, their signals can be deemed similar to the simple form of human language.
Ghazanfar, Asif, and Drew Rendall. “Evolution of Human Vocal Production.” Current Biology 18.11 (2008): 457-460. Print.
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Hauser, Marc. “Costs of Deception: Cheaters are Punished in Rhesus Monkeys (Macaca Mulatta).” Proceedings of the National Academy of Sciences 89.24 (1992): 12137-12139. Print.
Pearce, John. Animal Learning and Cognition: An Introduction, New York: Psychology Press. 2013. Print.
Seyfarth, Robert, Dorothy Cheney, and Peter Marler. “Monkey Responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication.” Science 210.4471 (1980): 801-803. Print.