that social neuroscience focuses on the dynamic interactions of the mind “with the biological systems of the brain and body and the social world in which it resides” (p. xiii). More specifically, Cacioppo and Decety (2011) define social neuroscience as the “interdisciplinary field devoted to the study of neural, hormonal, cellular, and genetic mechanisms, and to the study of the associations and influences between social and biological levels of organization” (p. 3). In short, social neuroscience examines the reciprocal or two-way relationship between physiology and social behavior (Matusall, Kaufmann, & Christen, 2011). Social neuroscience’s ability to map social behavior onto specific regions of the brain permits inferences about the functions of those regions in the enactment of social behavior (Ochsner, 2007). Such mapping allows researchers to deepen their understanding of how the brain creates social behavior (Ochsner, 2007). Given the special status that social behavior has in the brain, one can argue that the brain is fundamentally a social brain that has evolved at least partially in response to specifically social pressures and affordances (Grossmann, 2015; Lieberman, 2010, 2013). Let’s now turn to a brief discussion of the origins of the social brain.
Dualism: The philosophical position that the mind and body are separate
Mind/Body Problem: Challenge of determining how the mind and the body are related
Social Neuroscience: Interdisciplinary field devoted to the study of neural, hormonal, cellular, and genetic mechanisms, and to the study of the associations and influences between social and biological levels of organization
Think Again!
1 What is the mind/body problem?
2 How does the notion of the embodied mind resolve the mind/body problem?
3 What is social neuroscience?
Origins of the Social Brain
Our brain can be seen as possessing a tripartite structure that consists of the reptilian, mammalian, and neomammalian or higher brains (Hirth, 2010; MacLean, 1973). The reptilian brain is, in evolutionary terms, the most ancient part of the brain and one that we largely share with lizards and similar species. The mammalian brain refers to structures of the brain, such as the amygdala, hippocampus, and thalamus, that play a central role in fear, aggression, hunger, thirst, and sex. The core functions of the mammalian brain revolve around basic physiological survival needs. Finally, the higher brain consists of the neocortex or outer layer of the cortex that we commonly associate with our most advanced brain functions, including reasoning, planning, personality, and language. The neocortex comprises a much larger portion of the brain in humans than in other species. Although this tripartite model is overly simplistic, it is useful as a quick sketch of the evolutionary origins and structure of the brain.
One of the most interesting questions regarding the human brain is how it evolved to its current size and complexity. In order to answer this, scientists have tried to identify the conditions and pressures that led to the appearance of the larger brain in our primate ancestors. A number of theories have been offered to explain this evolutionary advance, but I’ll discuss two types of explanations: ecological and social (R. Dunbar, 1998; Gamble, Gowlett, & Dunbar, 2014). Ecological theories hold that the larger, more intelligent brain is a consequence of features of the nonsocial environment, such as climate or geography. One theory is that as primates increasingly relied on fruit for sustenance, they needed to be able to maintain mental maps of the locations of various fruits and keep track of when they were likely to ripen (R. Dunbar, 2011; Harvey, Clutton-Brock, & Mace, 1980). Such detailed and extensive mapping would have required considerable cognitive ability, and those who were better able to remember where food was located—presumably those with slightly larger brains—would have been more likely to survive and reproduce.
HUMAN EVOLUTION Conceptual image depicting the stages in the evolution of humans. At lower center is an amphibian creature rising from the water. These evolved into the first land vertebrates 360 million years ago. Clockwise from this are proconsul (23–15 million years ago) depicted as an African ape with both primitive and advanced features; Australopithecus afarensis (4–2.5 million years ago), which displayed a bipedal, upright gait walking on two legs; Homo erectus (1.5 million years ago) used fire and wooden tools; and Homo sapiens or modern man, who appeared 300,000–200,000 years ago).
Christian Jegou Publiphoto Diffusion / Science Source.
An alternative ecological hypothesis states that greater intellectual capacities were necessary to be able to extract the most nutritious components from food sources, such as nuts and seeds (Parker & Gibson, 1977; Walker, Burger, Wagner, & Von Rueden, 2006). Thus the more intelligent individuals would able to maintain their own health and strength as well as those of their mates and offspring, and consequently, their gene pool was more likely to be passed along. The premise of both these theories is that nonsocial pressures were the primarily drivers of the increase in brain size.
In contrast, the social brain hypothesis holds that greater intelligence was required to monitor increasingly complex social networks (R. Dunbar, 1998, 2011; Humphrey, 1976; Stevens & King, 2013). That is, with larger communities comes more frequent interaction with greater numbers of people, and in order to successfully negotiate all of the social relationships among members of a community, an individual needed to be able to predict the consequences of his or her behavior and the behavior of others. Furthermore, larger communities required more hierarchy, alliances, and cooperation and the need to keep track of them all. In other words, successful navigation of these complex social networks required greater social intelligence (Humphrey, 1976).
Dunbar (1993, 1998; R. I. M. Dunbar, 2014) provided an empirical test of these competing models by seeing how well variations in diet or community size predicted social intelligence. As an index of social intelligence, Dunbar used what he called the neocortex ratio, which is the quotient of the neocortex volume divided by the volume of the rest of the brain. Higher neocortex ratios reflect enhanced ability for complex reasoning, planning, and greater social intelligence. By plotting the neocortex ratios of various nonhuman primate groups against appropriate comparison measures—percent of fruit in the diet or group size—it became clear that trends in group size fit much better with the data and therefore more adequately explained the origin of our sophisticated brains (see Figure 2.2). In other words, there is a positive correlation between neocortex ratio and group size, but no correlation between the ratio and fruit consumption. The human brain, as you can see, is truly social, both in terms of how it processes information and in the way that it evolved (Mercer, 2013; Vugt & Kameda, 2014).
Figure 2.2 Origin of the Social Brain
Source: Gamble, C., Gowlett, J., & Dunbar, R. (2014). Thinking big: How the evolution of social life shaped the human mind. London: Thames & Hudson.
Neocortex Ratio: Quotient of the neocortex volume divided by the volume of the rest of the brain
Think Again!
1 What is the tripartite brain?
2 What is the ecological perspective on the origins of the big brain?
3 What is the social brain hypothesis?
Self-Reflection 2.1
When
