For humans and nonhuman primates, communication through vocalization is a key factor in social interactions. While human vocalization may sound very different than that of nonhuman primates, much of the signals are used to express similar emotions and feelings. Not only is the intentionality of the signals similar, but also the voiced sounds begin at the “vocal folds of the larynx” for both humans and nonhuman primates (Seyfarth, lec). Thus, even though there are clear differences in the vocalization of humans and nonhuman primates, the anatomy of the vocal apparatus does have similar features in both species.
Production Mechanism
While the source of the sounds includes “vibration” in the same part of the larynx for both humans and nonhuman primates, the larynx is positioned differently in both species. In humans, the larynx is placed at a lower position of the vocal tract than it is in nonhuman primates. Another anatomical difference is found in the thoracic vertebral canal, in which humans have more of an “expanded canal” than nonhuman primates (Seyfarth, lec). Not only do humans have a bigger canal, but they also don’t have air sacs such as nonhuman primates. These air sacs are meant to “allow for higher calling rates and longer bouts” (Seyfarth, lec). This difference alone makes sense because nonhuman primates require to be heard at longer distances to warn their community about potential dangers.

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Acoustic structure & degree of complexity of the signals
While nonhuman primates have obvious environmental differences than humans, both of these species have two aspects of the vocal production system that are imperative to communication. These aspects are called voice pitch and voice timbre (Ghazanfar). When the vibration of the larynx occurs, there is “highly patterned sound source” which creates a frequency (Ghazanfar). After a steady frequency is created, the vocal tract airways on top of the larynx and the sound pass out the lips through air filters in both species. The only difference then is how the filter passes out of an ascended larynx in nonhuman primates and a descended larynx in humans.

Range of meanings that the signals convey
Each signal that is made convey different meanings for both humans and nonhuman primates. However, in nonhuman primates the differences far outweigh that of humans. For example, a field recording found that vervets produced 3 different acoustical alarm calls when it came to dangers from leapards, matial eagles and pythons (Seyfarth). The leapord alarms were “short tonal calls,” the eagle alarms were “low-pitched,staccato grunts” and the snake alarms were “high-pitched” (Seyfarth). In addition, each type of alarm was linked to a difference response and behavior. For example, if monkeys were on land when they heard the leopard alarms they’d run up a tree to be away from potential danger. When the eagle alarm was heard, the monkeys would swiftly look up or hide in a brush where they couldn’t be found. Thus, the “variation in the acoustical structure” from different alarm call sounds was a primary part of explaining why the monkeys responded differently. This shows how emotional states were triggered in the monkeys through different sounds and how behaviors could thus be changed as well.

Intentionality in the use of vocal signals in nonhuman primate environments
When different sounds were heard by different species, monkeys reacted very differently. Changes in behaviors also occurred within animals living in a tight knit social environment in which they may have observed how to behave so as to remain free from punishment from the elders or superiors in their community. This is where the idea of “theory of mind” comes into play. For humans, when a person uses language to try and change another person’s mind this is called theory of mind. In nonhuman primates, manipulative behavior changes can occur through use of deception in vocalizing information. This is why this is a common occurrence in social environments where communication is ongoing and behavior mechanisms set. It’s as if “the presence of one animal can influence what another learns” and this can turn into observational conditionings that last a lifetime for the nonhuman primate (Animal Learning and Cognition). If a monkey, for example, has constantly observed his or her superiors getting first dibs on food or the females in the community, the monkey will learn that this is simply the way everything works. Thus, the monkey will gain a habit to allow the superiors to eat first or get first dibs on choosing a female to avoid punishment or getting ousted from the social environment (Animal Learning and Cognition). Therefore, while some researchers argue that nonhuman primates do indeed have a theory of mind others don’t believe this is true. Instead they argue that behaviors are learned and adjusted to, however if a superior monkey can change the reactions of an inferior monkey even in a lab setting; this fits well with theory of mind.

Conclusion
Both humans and nonhuman primates have similarities in their anatomical vocal tract structure with humans having an ascended position of the larynx. However, these anatomical similarities don’t mean that the signals conveyed represent similar messages. Since nonhuman primates live in an environment that poses many outside threats a lot of communication is done to communicate just this to the community. On the contrary, humans might try and use theory of mind to change someone else’s mind. Nonhuman primates, on the other hand, can use deception to get their way as well leaving the question of what exactly is the intention of all vocal signals in nonhuman primates? Of course, further research will answer this but for now it can be concluded that nonhuman primates do indeed know what they are conveying when they are vocalizing in a much similar way that a human knows when its trying to manipulate someone for his or her favor.

    References
  • Seyfarth, Robert M. “Monkey Responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication.”
  • Ghazanfar, Asif A. “Evolution of human vocal production.”
  • Seyfarth, Robert M. “Anatomy of the vocal apparatus.”