by Jennifer FortunatoIn Dunbar and Schultz, they discuss the topic of how and why the brain has evolved to be larger, compared to body size, in mammals. They initially discuss ecologically and ontogenetically important reasons for why this may have occurred, for example foraging and efficient energy use respectively. They then go deeper into the social aspect of why the brain has gotten larger in mammals, and a few other species including birds. They consider social complexity, pair bonds, and the microbiology of the brain to try to explain why the brain has gotten larger in these species than needed to maintain the body.
Dunbar and Shultz’s analysis of social complexity involves discussion of the importance of living in a social group and the challenges that come with it. For example, the authors examine how group cohesion and brain size relate to one another. Group cohesion mechanisms such as technical innovation and food acquisition via social learning comes with survival and increased effectiveness in reproduction. This group cohesion correlates with a larger brain size. Another beneficial aspect of social groups is minimizing predation risk. They argue that the selection pressure to minimize predation risk by being social will increase brain size due to those who have larger brain having higher fitness. The authors also extend their analysis beyond primates to other related species such as birds, bats, and ungulates (hoofed animals). They recognized that there are some mixed results in attempts to apply sociality as a reason for increased brain size in these other animal species. Dunbar and Shultz briefly discuss the hypothesis that sexual selection is a driver of larger brain sizes but conclude that there is no evidence for this. They then go on to discuss pairbonds as an important factor in brain size evolution. Anthropoid, or human like, primates have, according to multiple data sources, a positive correlation between brain and social group size. An issue that the authors came across was what bondedness actually entails as they determined it is an emotional state rather than one that can be quantified. Dunbar and Shultz argue for the idea that higher vertebrates, such as primates, have a more complex version of social bonding than other species. They do so by analyzing how social relationships in primates differ from those of other species because the social interaction to benefit the group will benefit the individual’s fitness down the line. Microneurobiology is the last point that Dunbar and Shultz discuss. They shortly discuss the function of hormones and genes in the role of brain growth. The authors dismiss these two aspects as an important role in brain growth and sociality. They relate these mechanistic approaches to developmental approaches to analyze brain size. Though an informative article in articulating possible solutions for the problem of brain size and brain growth, I do have a few criticisms. Dunbar and Shultz focus on entirely on sociality being a fundamental driver for the increase in brain size. However, sociality could be a by-product of ecological and life history constraints (Brooks et al. 2017, Armitage 1981). This would indicate that it is these constraints that actually influence brain size rather than sociality itself. Also, in direct contradiction is a later article by DeCasien et al. (2017) that argues that primate brain size is predicted by diet and not sociality. This furthers the argument for increased brain size being more related to ecological factors than sociality. Dunbar and Shultz also discuss the importance of having a large brain in comparison to body size as an important feature of mammals and birds and how that relates to sociality. However, they fail to take into account both invertebrates, such as ants, and very large mammals, such as whales, whose brain sizes are considerably larger or smaller respectively. Both ants and whales have complex social structures but have completely different brain size to body ratio with ants having 14% and whales having less than 1% of their body weight being their brain (Seid et al 2011, Koch 2016). This seems to go against Dunbar and Shultz’s argument that having a larger brain is a strong correlate with sociality. Overall, this article brings up good points about the evolution of social brain in primates, though it does leave out an entire group of social insects. Dunbar and Shultz have brought up a multitude of avenues of study for neuroanthropologists. For example, analyzing how bondedness can be quantified in non-human primates. Another line of study could be the integration of molecular, behavioral, and phylogenetic data of how the social brain has come to evolve both in size and other aspects. As neuroanthropology is an integrative field, the integration of multiple techniques from psychology, biology, and anthropology can be utilized to understand the evolution of the size of brain in a social context. References:
7 Comments
Elisabeth Nations
1/22/2019 09:00:30 pm
I think the concept of encephalization being intrinsically linked to social complexity rings true. It certainly stands to reason that increased brain size and increased social complexity would help fend off predation, which would then encourage the further increase of both those factors. I am a little skeptical about Dunbar and Schultz's ideas about encephalization's relationship to pairbonding. It's logical that pairbonding might be easier with greater brain capabilities, as a close monogamous relationship might take more work so that those two creatures can live and work harmoniously. What I don't understand is how pairbonding and monogamy would contribute to the evolutionary drive for bigger brains; it doesn't seem as though pairbonding would have much more of an effect on reproductive success and fitness than polygamy, or some other sort of social structure.
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Elisabeth Nations
2/26/2019 05:18:28 pm
I had originally been skeptical of the claim made in this paper that pairbonding played a large role in encephalization, but now that I reflect on our class discussion I appreciate this essay a little more. This paper discussed pairbonding mostly as a sort of monogamous reproductive relationship, but if we think of pairbonding as simply forming close relationships with other creatures, then the argument for pairbonding leading to encephalization is much more persuasive. After all, forming a complex network of social relationships is incredibly adaptive, given that these relationships can make it easier to find food, fight off predators, and successfully reproduce. Although this blog post brings up some interesting points about how this theory may or may not apply to other species, I think that the uniqueness of anthropoids being able to track relationships over long periods of time and to form vast social networks of both friends and adversaries makes it pretty evident that social complexity and relationship-building does lead to encephalization.
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Vanessa Marshall
1/22/2019 09:23:55 pm
For someone who does not have an extensive background in primates, evolution, or brain development, I really appreciated how Dunbar and Shultz laid out the historical, current, and newest theories about why large brains evolved. I was a little confused by the interplay of ecological and social problems -- it seems that they influence each other and separating them experimentally seems near impossible. The qualitative vs quantitative relationships between brain size and sociality and social group size, respectfully, confused me as well. Do you have any insights as to why they made this distinction? I agree with Elisabeth about not quite grasping why monogamy (as opposed to polygamy) is emphasized in the paper. Perhaps it is a correlation that was noted, but causal relationships have not been explored or documented yet. I wish that the short section on microneurobiology had been developed as well as the rest of the paper, because as a microbiology student, these interactions really interest me.
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Kaitlyn May
1/23/2019 04:58:05 am
I also appreciated how well Dunbar & Schultz presented current research on how and why human brains evolved to be large. The relationship between encephalization and social complexity can easily be understood as an evolutionary advantage, even for someone without a strong background in the field. This discussion, however, made me consider current levels of sociality, and how this has changed even within our generation. In today's social media age, although sociality has seemingly increased via the explosion of social media platforms, many social psychology researchers argue that we live in a markedly isolated, unsocial age. I am curious how an anthropologist would define this shift, if at all.
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Moe Prince
2/27/2019 07:44:47 am
The theory that makes the most sense for why primate brains developed so much more than other animals has to do with their social network. Becoming a more difficult prey also contributes greatly to this. I found this article super interesting due to the fact that there is still some mystery behind it.
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Vanessa Marshall
2/27/2019 09:58:54 pm
The idea of group cohesion as a result of technology and foraging via social learning, which then selects for larger brains still interests me as a likely theory for the continued development of large brains. As primates evolved to be more socially complex, and the gut changed to require less, but higher quality foods, more free time became available. And being socially complex, the responsible neural networks need to be fulfilled in some way. I think sports as culturally significant rituals developed because of or at least partially due to a need for constant group cohesion. Since reading this Dunbar and Shultz article, we also read and discussed capoeira as a musculoskeletal exercise that changes neural networks and is affected by culture. I think there must be a bidirectionality here that feedback loop reinforces these cultural sports (rituals) as a method of continual group cohesion. If a social group is not constantly diffusing tensions and creating social bonds, then are the previous bonds disappearing? I would think so. Neural networks are constantly reinforced by social interactions, and thus continual group cohesion has been enabled by sports which continues the evolutionary selection for larger brains.
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1/24/2022 02:00:28 am
I found this article very interesting, thanks for sharing
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AuthorThis blog is group authored by Dr. DeCaro and the students in his ANT 474/574: Neuroanthropology. Archives
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