The Following is a brief summary of “Understanding Primate Brain Evolution” by R.I.M Dunbar and Susan Shultz. The researcher begin by describing the original social brain hypothesis, which was used to explain why primates have larger brains compared to their body size when compared to other vertebrates. Throughout this explanation they state that the limiting factor for research into the limit of the social brain hypothesis is the small amount of attempts to to evaluate if the relationship between brain size and group size is truly bound to these variables. Their points to prove throughout the research were to:
- confirm the original findings hold up to not only primates but a wider perspective across the mammalian spectrum, and
- View brain evolution within a broader perspective.
As the social brain hypothesis was extensively tested on primates, research from Perez-Barberia & Gordon (2005) and Shultz & Dunbar (2006) have been able to show that social species have a larger brain. It was also considered that habitat may play a part as those in mixed habitats had a larger brain than that of the mammals in the open or closed habitat. Dunbar and Shultz stated, “that the two traits are under tightly coupled selection; changes in one trait (sociality) are only possible if they are associated with changes in the other trait (brain size)”
Perez-Barberia’s analysis provided a hand for lagging evolution throughout the 3 different habitats but did not find consistent pathways for these findings. Thus providing a “flexibility” or lack of cohesion within the groups.
To evaluate a in greater depth the relationship between brain size and association between species-specific behavioral, ecological, life-history characteristics, etc to the social brain hypothesis, Shultz & Dunbar created an evaluation in which a three-step analysis.
- the univariate analyses in which the different behavioral and ecological traits are measured with how much they associate with measures of the brain size.
- the use of general linear models to test alternative models of the characteristics and how they relate to both brain size and being social.
- They built a test a path model to integrate life history, ecology and social complexity as causes and consequences of brain size.
With this test they found that the brain volume correlates with the sociality of the vertebrates. In primates particularly, it is a strong relationship to the size of the social group but more importantly the act of “social play”.
Along with the size of the brain it was found that the neocortex in some cases also appeared larger within primates. Pointing to the importance of the frontal lobe.
With this information discovered, they have a very small look as to how the brain produces these effects and suggested that as brain size increases, a disproportioned computational power becomes available. Thus allowing for increasingly sophistication in social behavior of the primate or animal in question.
The experiment as a whole is a very grand idea and gave one a closer insight into the wonders of the brain and how ones surrounding can affect characteristics like sociality or brain size. I would want to look more into the genetic mechanics behind this or if they in fact play a part big or small into the outcome of the brain size, learning, or intelligence level.
The following is a brief summary of chapter 3 of the book “The Encultured Brain: An Introduction to Neuroanthropology” edited by Daniel H. Lende and Greg Downey. The title of the chapter is “Primate Social Cognition, Human Evolution, and Niche Construction: A Core Context for Neuroanthropology.” It was written by Catherine C. MacKinnon and Augustine Fuentes. The authors begin their discussion with the background of primatology. In the 1930s up through the 1950s researchers were focused on studies of social behavior and ecology of the nonhuman primates. In 1951, Sherwood Washburn called for a “new physical anthropology” in which research would integrate laboratory and field studies, examine comparative anatomy and functional morphology, and describe the links between ecology and behavior. In the 1960s and the 1970s fieldwork was conducted with chimpanzees, mountain gorillas, and orangutans by researchers such as Jane Goodall, Diane Fosse, and Birute Galdikas. In the field of psychology, Harry Harlow conducted his notorious experiments on the significance of primate mother – infant attachment and social bonding. In the 1970s and the 1980s the focus turned to social biology and evolutionary psychology. Here researchers focused on how human brains gained cognitive components that evolved to solve the reproductive problems faced by our hunter gatherer ancestors.
Primates, including humans, share various general characteristics including; prehensile hands and feet, a reliance on visual and tactile sensory pathways, extended periods of infant dependency and development, and significantly enlarged brain to body size ratios. The expansion of the visual system is seen as being tied to sociality. Primates must be able to read complex social signals and their emotional content. Among primates there is a strong tendency towards sociality and group living. Physical and emotional bonding and social attachment have been determined to be crucial for the healthy development of the central nervous system. Primates employ color vision to help find foods, use their memory in the spatial mapping of resources, and communicate about food sources as well as predators. The authors suggest that our brain and our visual system selectively focus on information which can protect us from potentially dangerous individuals or situations. Advanced cognitive structures allow primates to display a great range of plasticity in foraging behavior and living environments.
Primates also engage in niche construction, which can be defined as the modification of the functional relationship between organisms and their environment by actively changing one or more of the factors in that environment. Through this process primates have significant effects on their environment which then affect their population. For example, responses to the energetic cost of increasing brain size and extended period of child rearing in genus Homo included more cooperation between group members, an increase in the complexity of communication, and increased effectiveness at avoiding predators and an expansion of the types of environments in which they live. This is also seen in other primate species. For example, female capuchins keep track of and maintain large social networks over the course of their lifetimes. Social organization characterized by fission-fusion groups and subgroups common among chimpanzees is another example. It is been observed that some members negotiate rank through aggression while others rely on coalition partners and social bonding. The authors conclude that a highly evolved social cognition is required to keep track of the social networks. The authors suggest that social network analysis can be a fruitful method allowing researchers to examine types of interactions among individuals in a social group. Social network analysis allows for the examination of complex patterns in which primates organize themselves socially.
Primates also share the characteristic of an extended period of dependency after birth. The level of social complexity is correlated to increased sizes of neo-cortices. Among the primates, humans have the least mature brain at birth followed by a period of rapid brain growth, influenced by an environment rich in social stimuli. It is also suggested that an increased consumption of animal protein also brought hominids in close competition with carnivores also resulting in an increase in brain size.
The cultural intelligence hypothesis suggests that humans have a species specific set of social cognitive skills for participating in and exchanging knowledge through particularly complex cultural groups. Among primates, research has found cooperative and altruistic behavior in certain situations with varying results. Chimps have been found that while in adjoining cages they will sometimes give tokens which produce a food reward for both of the animals. It is also been shown in laboratory research that capuchins may value equitable behavior. In conclusion, research suggests that primates display extensive plasticity in sociality and cognitive functioning which results in increasing brain size, social complexity, and evolutionary success via biosocial niche construction.