Monkey See, (Evolved) Monkey Do: A Reminder of Where our Communicative Abilities Came From

Communication is the essence of human life. Unlike many organisms, our day-to-day activities depend upon the ability to speak, listen, and comprehend each other. While animal communication occurs even in the most basic organisms—often through simple chemical or photoreceptive mechanisms—humans have rapidly evolved complex physical and cognitive abilities unparalleled by any other species. Yet we often forget that the processes and structures that drive our social interactions are not unique to humans, consequently perceiving ourselves to be a superior species. Over the past few years, research using comparative anatomical neuroimaging of humans and other primates (2) and behavioral studies of non-vocal communication strategies among primate species (3) has uncovered a surprising number of examples of shared communicative abilities between humans and other primates that reinforce established phylogenetic relationships (1) and serve as an important reminder of the close evolutionary relationship we share with these organisms.

            Since the advent of genomic sequencing, there have been countless studies dedicated to investigating the evolutionary relationship between humans and primates. Although it is often a topic of debate in the non-scientific community, there is strong phylogenetic evidence, as depicted in Figure 1, which shows humans to be most closely related to chimpanzees and bonobos in a DNA comparison of non-hominid ancestral species. For example, scientists uncovered an orthologous transcription factor in both humans and chimpanzees that controls expression of genes in the brain that are associated with human language capabilities (1).

Figure 1. The commonly accepted evolutionary relationships between major primate groups derived from genome sequencing. As shown in the phylogeny, humans share a most recent, non-hominid ancestor with chimpanzees and bonobos. Note: Figure 1 adapted from (1).

Yet while researchers celebrate the discovery of one more piece of the primates’ homological puzzle, most people remain unimpressed by seemingly invisible genetic data.  Remedios et al (2) begin to break down the barrier between common understanding and scientific obscurity through a comparison of non-vocal communicative behavior in humans and other primates. Humans have always displayed strong non-vocal influences in their communication. For example, there are specific universal facial expressions to convey a particular emotion, and we create music and rhythm to capture ideas and sentiments that can be share by others in our culture or society simply by experience. It was found that, like humans, monkeys will drum on surfaces in their environment in conjunction with vocal sounds to create patterns recognized by other individuals in specific parts of the brain. Just as humans vary tone or pitch to convey emotion, different volumes and other acoustic variations could present social information, such as power or strength (2). These uncanny similarities between human and macaque behavior demonstrate the shared trait of behavioral expression in communication among primates, supporting the idea that humans are not as different from other species as we often believe.

            Furthermore, the response to such behavioral patterns was very specific. In individuals exposed to vocalizations and natural environment sounds, macaques showed increased activity in the temporal lobe when listening to vocal sounds. Interestingly, in a review of neurological findings Wilson & Petkov (3) highlighted a comparison of brain images from humans, chimpanzees, and macaques under similar test conditions and noted the tendency for all three groups to have recognition for vocal communication in the temporal lobe. Figure 2 visualizes the location of these areas, showing that primates are not only interconnected at a behavioral level, but also at an anatomical level. Wilson & Petkov (3) also explain that changes in brain images occur when certain vocalizations or noises change in the environment, suggesting there is semantic meaning behind certain sounds. This helps us understand Remedios et al’s (2) findings: different drumming sounds have unique contextual meaning, much like a rudimentary version of human language. A form of constant, reliable, comprehensible communication is essential to survival for humans, so it is logical that our ancestors would need a similar ability, such as the one used by macaques.

Figure 2. A comparison of temporal lobe areas specific to vocalizations, voice identity, and general voice sensitivity in primate brains as derived from brain images of individuals from each group. The results suggest there are analogous areas for species-specific vocalizations in all groups, and for voice identity sensitive areas between macaques and humans, suggesting a shared ancestral ability to use areas of the temporal lobe for vocal communication. Note: Figure 2 adapted from (3).

            While there is still much work to be done to fully understand the similarities between the communication mechanisms in different primate species, it is clear that there are underlying patterns shared by many distinct groups that have an ancestral origin. It is important to be able to visualize these patterns in order to better understand that humans are not above all species, but rather interconnected. As Darwin succinctly wrote, “The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind (1),” reminding us that to live in this world, we must see ourselves as part of the natural community, not above it.

Cited Literature:

1.     Goodman, M & Sterner, K. N. (2010) Phylogenomic evidence of adaptive evolution in the

ancestry of humans. Proceedings of the National Academy of Sciences 107, 8918-8923.

2.     Remedios, R., et al (2009) Monkey drumming reveals common

networks for perceiving vocal and nonvocal communication sounds. Proceedings of the National Academy of Sciences 106 (42), 18010-18015.

3.     Wilson, B. & Petkov, C. I. (2011) Communication and the Primate Brain; Insights from

Neuroimaging Studies in Humans, Chimpanzees and Macaques. Human Biology 83 (2), 175-189.