By: Patricia cartwright
Writing about the quirks of human nature.
Evidence supporting SBH:
Despite the evidence refuting the SBH, it prevails as a widely-cited explanation for brain evolution for several reasons. First, the hypothesis has received increasing empirical support that has found the size of the neocortex to be strongly associated with indices of social complexities (Dunbar & Shultz, 2007). For instance, the relationship cited by Dunbar between neocortex size and group size of various mammals has been replicated by other researchers in the field (Finlay & Darlington, 1995; Byrne & Corp, 2004). Secondly, given the expensive energy costs associated with utilizing higher cognitive brain functions, it is a well-reasoned argument that there is some beneficial social advantage that has driven brain evolution (Dunbar et al., 2007).
Critiques and counterpoints: In extant literature, the SBH is widely favored as an explanation for the evolution of large brains in humans and primates, over traditional explanations based on ecological or developmental problem solving (Dunbar & Shultz, 2007). The traditional explanations of the evolution of the human brain had a tendency to narrowly emphasize the need for specific abilities such sensory and technical competencies (e.g., way-finding or mental mapping and scavenging) as the reason behind the human brain expansion (Dunbar et al. 2007). Although the SBH is more comprehensive in nature than traditional explanations, it contains several shortcomings that should be brought to light.
The SBH, for instance, cannot adequately account for grade shifts or why certain species such as Orangutans and aye ayes possess unusually large brains. This is particularly surprising given the simplistic structure and nature of their social hierarchy and environments (van Schaik et al. 2012). Moreover, the SBH does not provide an explanation for why mammalian lineages have significantly smaller brains but possess equal socio-cognitive abilities and function in equally complex relationship dynamic societies (van Schaik et al. 2012). Likewise, when looking at other species such as small-brained fish, the SBH is not able to account for the ability of this species to exhibit socio-cognitive abilities that match that of primates (van Schaik et al. 2012). Moreover, in Tim Ingold’s critique of the SBH, he points out that the data supporting the SBH has been selective and confirmatory in nature. Although the SBH may not be able to adequately explain brain size for all mammalian lineages, it may be the best explanation we have for humans and primates.
The Magic Number
One of the two final counterpoints to be considered is the argument that the complexities of social relationships may be due to the evolution of mammalian intelligence, rather than the demands an increase in social group size brings. Intelligent individuals bring their own challenges, so it is reasonable to argue that this relationship may be flipped. A second and final counterpoint to be considered is with Dunbar’s number. This theory posits that 150 is the cognitive limit of people that one person can maintain stable relationships with. Since Dunbar’s research on this theory, Dunbar’s number has been found to have an upper limit, which does not necessarily invalidate Dunbar’s number but it calls it into question (Kanai et al. 2012; McCarty et al. 2001; MacCarron et al., 2016).
Most theories tend to test one research question before ascertaining whether alternative, equally plausible explanations could also make the same predictions (Dunbar & Shultz, 2007). |
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