by Samuel ScopelIn Chapter 3 of The Encultured Brain, which focuses on social cognition in primates, the authors cite evidence suggesting that expansion of the visual system is characteristic of the primate brain. While improved vision is beneficial for a number of reasons, such as locating food, predator avoidance, etc., none of these are unique to the lives of primates, and primates are not particularly noteworthy for their visual acuity within the larger mammal family. One explanation proposed by a number of studies is that sociality contributed to this expansion. Recognizing visual cues, such as body or facial gestures, and evaluating these cues within their larger social context requires significant visual processing capacity.
In “Signals use by leaders in Macaca tonkeana and Macaca mulatta: group-mate recruitment and behaviour monitoring,” the authors examine the interplay between visual cues and coordinated social movements. In primates that live in groups, there are often specific areas designated for a given activity such as foraging or resting. To retain the benefits conferred by performing activities as a social unit, movement between these areas must be done as a group and requires consensus among the individuals composing the group. In this study, Sueur and Petit examine the visual cues utilized by the individual initiating the movement as well as how those cues are modulated based on the members of the group that chose join. In Tonkean and rhesus macaques, the primate species observed during the study, the individual wishing to initiate a collective movement will begin moving in the desired direction and pauses and back-glances cue other group members of the intent. The authors monitored how the frequency of both these cues affected the actions of fellow group members, and how the number and identity of the joiners affected the behavior of the initiator. In general, pauses and back-glances decreased significantly when the desired individuals joined the initiator in both species. The authors grappled with whether pausing was a direct cue to specific group members to join the effort or an expression of uncertainty on the part of the individual initiating the movement. If pausing was an expression of general uncertainty, then pausing should decrease with the number of contemporaries joining the movement regardless of who the joiners were. Interestingly, the authors observed that pausing only decreased when certain members joined the group, suggesting that the pause signal was intended to recruit specific group members to join the action. The only substantive difference noted between species was that Tonkean macaques tended to emphasize recruiting affiliated individuals and rhesus macaques decreased pauses when kin-related individuals joined. The authors hypothesized back-glances were mainly used to monitor the number/identities of the group members joining the collective effort. One limitation noted by the authors was the semi-free ranging conditions in which these observations were performed. The distances between individuals was lower and general visibility higher than what would be found in natural populations. Other behavioral factors, such as calls, may play a more significant role in natural conditions. This study highlights just one example of how visual indicators contribute to social efforts and facilitate group cohesion. It stands to reason, given the number and variety of activities in which primates take part in a social context, that the expansion of the area of the brain responsible for visual processing observed in primates would provide a selective advantage. While this study alone is insufficient evidence for this proposition, one could imagine how sociality could function as a positive feedback loop driving evolution of regions of the brain that are critical for operating within it. Primates that are more effective at coordinating social activities (ie resource management, group defense, etc.) would lead to fewer individuals being lost to predation or other miscellaneous selective pressures that are more evident in species that can only operate in a solitary capacity. This would, in turn, lead to a more pronounced emphasis on the refinement of inter-individual communication and the physical structures or processes associated with it. Paper: Sueur, C. & Petit, O. Signals use by leaders in Macaca tonkeana and Macaca mulatta: Group-mate recruitment and behaviour monitoring. Animal Cognition 13, 239–248 (2010).
4 Comments
Zach Obaji
1/23/2019 03:53:47 am
I enjoyed reading your blog post, and I found the additional reading on signals and their use by signal leaders to be quite interesting. I am a bit confused by your first paragraph where you mentioned that Mackinnon and Fuentes may have focused too much on the expansion of the visual system. Later you claim that an explanation backed by studies points to sociality. However, on page 79, the authors talk about Cognition and Sociality. Nevertheless, the additional reading supplemented the chapter very well. The study's use of temporal analyses to determine whether the function of behaviors differed between the species was cool. The pauses and back-glances were especially interesting to read, and the alternative explanation claiming that these pauses could have been caused by uncertainty for going alone or hesitation was really neat. This study could have involved human primates for all we know; it is remarkable how close we are to non-human primates. If the study had involved human children, I bet there would be much hesitation. Random and weird, I know. Great work with this!
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Daniel Quillen
1/23/2019 09:37:52 am
I found this post fascinating in respect to how visual processing could have been a driving pressure for the evolution of larger brains in primates. Humans have multiple visual processing areas in the brain the main one being the visual cortex. The VC connects to almost the entirety of the brain and their is a specific lobe that's function is exclusively facial recognition in the amygdala. It seems that in order to survive in a complex society it would be imperative to process the facial and body language cues from other members of your society promoting larger brain development in visual processing.
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Zach Obaji
2/27/2019 06:10:35 pm
Earlier in the semester, it was difficult to fully grasp the correlation between social cognition and neuroanthropology. As the semester progressed, it is now easier to comprehend how large of a role social cognition plays in the discipline. After learning more about primate brain evolution, I was fascinated reading about the brain's extensive neural networks and its role in processing social interactions in primate brains. The neural circuity role in social plasticity as an adaptive mechanism was interesting to read about. The chapter provides an example to this by explaining how capuchin monkeys are able to discriminate after looking at photos of other monkeys.
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1/24/2022 02:02:21 am
Great article source to read. Thank you for sharing this.
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AuthorThis blog is group authored by Dr. DeCaro and the students in his ANT 474/574: Neuroanthropology. Archives
April 2019
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