By: Mary moussa Rogers
Clinical Doctoral Student at Mississippi State University
Evolution and the brain
Part of understanding human behavior is understanding the brain and its origins. In order to understand why the brain functions the way it does, it must be determined why and how it developed. The best way to examine how specific biological aspects have developed over time is by taking an evolutionary perspective. Evolution suggests that through the process of natural selection, changes occur in biology that are maintained if they increase or maintain the fitness of an animal (Gould, 1982). Fitness is an animal’s ability to reproduce and for their offspring to reproduce, and thus if a change occurs that increases the fitness of an animal, other animals without that adaptation may reproduce less and thus naturally select out the trait with less fitness (Gould, 1982). Part of what makes humans biologically different as a species is the large neocortex, which is thought to increase the fitness of humans. It was suspected that the brains development was due to its role in technical skills or sensation, but the evidence has begun to point elsewhere.
The complex social structure of humans and their primate ancestors
According to Dunbar and Shultz (2007), the development of the large neocortex is due to the significant requirements of the complex social system of humans. Specifically, they suggest that this developed due to primate sociality. Primate societies are based on “bonded relationships” or strong relationships outside of mated couples (Dunbar & Shultz, 2007). It was also shown that the neocortex size was linked to the size of the primates’ social groups, suggesting that human social groups size had something to do with its complexity and neocortex size (Dunbar & Shultz, 2007). The complex social lives lead by primates can be linked to larger brain size and empirical evidence suggests that all species that pairbond or bond with one mate have larger brains, but also primates bond with their mates and platonically which requires more brain matter (Dunbar & Shultz, 2007). Furthermore, evidence suggests that people with larger friend groups may be more likely to have a higher density of gray matter in specific areas of the neocortex, such as the amygdala (Von Der Heide, Vyas, & Olson, 2014). Other behaviors associated with the complex social groups of primates include male mating strategies, social play, and alliances within primate groups (Dunbar & Shultz, 2007).
Peacocks have twice the autonomy the giraffes and the tigers do
Although Dunbar and Shultz do an excellent job positing evidence for the social brain hypothesis, they fail to fully address the role of consciousness and reproduction. Furthermore, while there is plenty of confirmatory evidence, they fail to address the constraints on their theory (Barrett, Henzi, & Rendall, 2007). In other words, how does having consciousness and close friends improve evolutionary fitness? van Vugt (2012) critiqued that the social brain hypothesis missed some of the more important nuances between the development of a political hierarchy and the social identity that exists today. Furthermore, the neurological evidence supporting the social brain hypothesis is only correlational, positing that we cannot presume one causes the other in determining whether the brain changed before or after changes in social structure (Barrett et al., 2007).
The analogical peacock hypothesis attempts to better address at least one of these critiques, which is what the large neocortex has to do with reproduction and consciousness. According to McKeown (2013), social hierarchy only plays part of the role in the size of the neocortex, the other part largely has to do with how females select male mates. He suggests as social hierarchy became more complex, males had to develop more complex signaling behaviors to let females know they were not only interested, but they had traits that were desirable to the females (McKeown, 2013). This required some “mind-reading” or developing the ability to know what signals were desirable (e.g. creativity) and interpret signals simultaneously. Females too, had to become more complex in their signaling as the number of females to a group increased and thus more “platonic pair-bonding” had to occur (McKeown, 2013). Thus, as the social structure became more complex, so did the desirability of what he refers to as “mental fitness” or factors such as humor, language, and intelligence (McKeown, 2013). Although the social brain hypothesis may seem more parsimonious than the analogical peacock hypothesis, it doesn’t explain some of the expected mechanisms between the neocortex and social structure.
Moving theory forward
In conclusion, the analogical peacock hypothesis seems promising by integrating the empirically supported social brain hypothesis with a more direct link to evolutionary fitness. There are still some critiques it does not address, such as the issue of consciousness and problems with constraints and causality, but it seems to be a step in the right direction. If a peacock is able to expend the resources to produce a tail that attracts mates, a human could be able to fund the brain in order to joke with a potential spouse.
- Barrett, L., Henzi, P., and Rendall, D. (2007). Social brains, simple minds: Does social complexity really require cognitive complexity? Biological Sciences. doi: 10.1098/rstb.2006.1995
- Colrain, I. M. (2011). Sleep and the brain. Neuropsychology Review. 21(1), 1-4.
- Dunbar, R. I. M. & Shultz, S., (2007). Evolution in the social brain. Social Cognition. 317, 1344-1347.
- Gould, S. J., (1982). Darwinism and the expansion of evolutionary theory. Science. 4544(216), 380-387.
- von der Heide, R., Vyas, G., & Olson, I. R., (2014). The social network-network: Size is predicted by brain structure and function in the amygdala and paralimbic regions. Social Cognitive and Affective Neuroscience. 9(12), 1962-72.
- Kaas, J. H., (1987). The organization of neocortex in mammals: Implications for theories of brain function. Annual Review. 38, 129-51.
- McKeown, G. J., (2013). The analogical peacock hypothesis: The sexual selection of mind-reading and relational cognition in human communication. Review of General Psychology. 17(3), 267-287.
- van Vugt, M., (2011). The missing link: Leadership, identity, and the social brain. British Journal of Psychology. 103, 177-179.