In chapter four, Greg Downey and Daniel H. Lende discuss the human brain and the many theories that talk about how and why humans have evolved differently than other primates. It begins by discussing the correlation between brain and body size in many animals and how humans have a disproportionately large brain compared to the body. While other mammals have developed better systems for eating and reproduction, human's brain size has caused potential problems in both highly necessary features of survival. The disproportionate aspects of our brain doesn't stop at its total size however, and can be seen even in the size of the different parts of our brain especially the neocortex. The chapter goes on to discuss how the connections in the brain create many of the differences we see both physically and that create some of our abilities culturally. Changes in environment can greatly affect the connections that developing brains make and with humans developing so much outside of the womb there are many differences between people. Humans are a very social species which has helped develop the distinctive way that our brains work. Children are dependent on others to take care of them and this long time of dependency gives humans the chance to teach offspring more and provides opportunities for more diversity. Our ability to pass down our knowledge allows us to build on it. This along with our ability to empathize and work with each other has shaped how our brain has developed.
 
With my background mostly centering around culture and religion, this chapter makes me think more about childrearing and the way that has a lasting impact on all humans. I'm interested in what ways environment and culture can create and change different connections in the brain and how drastic these differences can be especially when looking at those who have experienced trauma or abuse.

In “Evolution of the Primate Brain,” Falk seeks to answer the question of “how humans came to be the largest-brained primate but also the most intelligent species on Earth” (Falk, 2014 pg. 1496). To best answer this question, we must study the evolution of the primate brain and the adaptations made early in primate brain evolution and how those early adaptations have influenced brain physiology of primates and humans. This is done by direct and comparative methods. The direct method is to study endocasts, or casts of the interior of braincases. These can be physical, fossilized endocasts and virtual endocasts created by 3DCT data, both allowing for the study of living and extinct species of primates (pg. 1498). The comparative methods are used to study living species and include histochemical, immunocytochemical, positron emission tomography (PET) scans, and functional magnetic resonance imaging (FMRI) scans. Using these methods, researchers can learn about neurons, including their types, sizes, densities, distributions, and connections, and about functional processing in the brain and how it works in terms of movement, sensation, sleep, preparation for action, thinking, and emotions (pg. 1499).

Apparently, there is some division among paleoanthropologists regarding the importance of absolute brain size and brain reorganization. Specifically, the argument is about which is superior. Falk provides in-depth analysis of both areas. In the sections devoted to the evolution of primate brain size, Falk discusses how to best interpret primate brain size, which is quite the undertaking due to the wide variation among primates. This wide range of brain size makes comparative study between primates difficult, so relative brain size, or RBS as it is referred to as in Falk’s paper, is used. RBS is a ratio between brain and body size. Falk discusses the methods that comparative studies use to eliminate the effects of allometric scaling on the brain. The quotients mentioned are the index of progression (IP) developed by Bauchot and Stephan and Jerison’s encephalization quotient (EQ). It should be noted that EQ heavily depends on the group being studied for baseline data and can easily overestimate the EQ of smaller-bodied species and underestimate the EQ of larger-bodied species (pg. 1501, 1503).

In later sections further delving into brain size of primates, Falk discusses studies done by Leigh that investigated two life-history strategies and their effects on infant brain grown and also two hypotheses that attempt to explain why primates (humans are included in this too) are able to grow large energetically expensive brains (the maternal energy hypothesis proposes that the mother’s basal metabolic rate during gestation determines neonatal brain mass and the expensive-tissue hypothesis says that encephalization is able to occur because of an evolutionary “trade-off” where amount of brain tissue has increased while the mass of other energetically expensive organs, like the heart, gut, liver, and kidneys has decreased) (pg. 1503-04). It should be noted that both hypotheses do not hold for bats and so their broader application in mammals is questionable.

Falk also gives an overview of encephalization in hominins, providing the detailed Table 1 on pages 1506 and 1507. Table 1 lists cranial capacities for Hominins as evidence to show the encephalization of hominin brains, but Falk says on page 1505 that “error may be introduced, however, because fossil endocasts are rarely whole and, thus, usually require partial reconstruction.” Later he writes “Although many workers have estimated EQ’s for fossil hominins, these estimates must be taken with a grain of salt because of the difficulty of determining surrogates for body mass” (Falk 2014, pg. 1507). Few intact femurs of hominins provide few accurate measures for determining body mass and size and therefore RBS.

Falk also discusses neurological reorganization because many believe that “size along is not enough to account for the observed diversity in primate behavior and that circuitry, neurochemistry, and subsystems must have been reorganized within brains to accommodate evolving behavioral repertoire” (pg. 1509). On page 1514 he mentions a study done by Semendegeri which dispels the idea that humans have abnormally large frontal lobes, which are larger due to allometric scaling, not because humans have better cognitive abilities (pg. 1514). It is also important to note that Neurological reorganization was not isolated to one area but was instead spread across multiple structures in the brain, dispelling the idea of a “mosaic evolution” evolution of the brain (pg. 1512). This is supported by the fact that high-order cognitive tasks engage areas of the brain across the cortical mantle and are not focused on one specific area (pg. 1512). Falk also mentions the role of mirror neurons in manual and orofacial communication in apes and humans and emphasizes the role of cortical asymmetries that are related to unique human behaviors like the tendency of right-handedness, symbolic language, and humanlike abilities for music, art, and technology (pg. 1516).

​Given that this is a Neuroanthropology class, the question of how this relates to Neuroanthropology and to the human brain should be at the forefront of our minds. This article seeks to answer the question of how humans came to be not only the largest-brained primate, but also the most intelligent - without ever having defined what, for the purposes of this paper, qualifies or quantifies the term “intelligence” or reaching any real conclusions. This is a valuable paper filled with information about endocasts and direct and comparative methods and the incredible range in primate brain size and the theorized ways that primates were able to support such an energetically expensive organ, but the answer to the ultimate question, how humans came to be the largest-brained primate and most intelligent animal, remains unanswered. We have theories and suggestions that seem to have merit because of the genetic closeness of humans and primates, but we do not have any concrete data that confirms these hypotheses.
 
Paper: Falk, D. (2014), Evolution of the Primate Brain. Handbook of Paleoanthropology, 1495:1518.

​Friederici (2017) provides a comprehensive review of research exploring the evolution of language. By reviewing structural and functional neuroanatomical differences between the primate and mature human brain, as well as comparisons between the phylogenesis and ontogenesis of language-relevant brain structures, Friederici provides a relevant timeline of the neural basis of language evolution while highlighting the specific aspects of language and neural structures which underpin this ability.
 
Friederici begins with a brief overview of the differing ways in which researchers define language. This then moves into a complex discussion of the computational mechanisms for human language. Though this section may be a bit daunting to those who are not well-versed in the language literature, Friederici does an admirable job breaking down difficult topics. Essentially, some researchers define language as all aspects of communication (facial expressions, hearing language, processing, etc.) while others focus specifically on the computational mechanisms behind how language is built. It is this construction aspect, and the complications of advanced grammar, that separates nonhuman primates from humans.
 
Friederici then begins reviewing studies of the neural mechanisms of human language. These studies overview differences in acquiring grammar systems in human and nonhuman primates, as well as the neurobiological bases of these grammar types. These studies conclude that the ability to master phrase structure grammar is uniquely human. Moreover, these studies highlight the neural mechanisms of language processing. Friederici first overviews the role of the posterior portion of Broca’s area (Brodmann area [BA 44]) in not only syntactic hierarchy building, but in the evolutionary pathway of language. Next, Friederici discusses the role of the inferior frontal gyrus, posterior temporal cortex, and the white matter fiber bundles connecting them to processing syntactically complex sentences.
 
The paper then moves into a review of cross-species comparisons of language. To date, there is no evidence that other species can process and learn hierarchically structured sequences. Friederici begins by noting that the posterior temporal cortex is larger in the left than the right hemisphere of both the human and chimpanzee brain, reflecting the left lateralization of language. In contrast, Broca’s area demonstrates distinct differences between cytoarchitecture, asymmetry, and developmental trajectories of human and nonhuman primates. Moreover, the dorsal pathway, a crucial pathway for the language ability in adult humans, is much weaker in nonhuman primates than in humans. These differences are postulated to reflect the behavioral trajectories in child language development as well as the lack of these behaviors in nonhuman primates. Friederici concludes that the differing asymmetries may be crucial to understanding the evolution of language.
 
Friederici (2017) provides an in-depth review to the neural circuits underlying the evolutionary pathway towards human language. Although does an excellent job reviewing a large body of relevant studies, the author neglects to include studies which indicate abilities of nonhuman primates to acquire human language skills, such as those in which chimpanzees learn to use American Sign Language (ASL). Although these studies typically admit limitations in the nonhuman primates abilities, they are still noteworthy to the evolution of language. Still, what Friederici does do nicely is provide a comprehensive understanding of the exact piece of language which is distinctly human—the ability to process and learn hierarchically structured sequences.
 
Reference: Friederici, A. D. (2017). Evolution of the neural language network, Psychonomics Bulletin and Review, 24, 41-47.

​In Chapter 3 of The Encultured Brain, which focuses on social cognition in primates, the authors cite evidence suggesting that expansion of the visual system is characteristic of the primate brain. While improved vision is beneficial for a number of reasons, such as locating food, predator avoidance, etc., none of these are unique to the lives of primates, and primates are not particularly noteworthy for their visual acuity within the larger mammal family. One explanation proposed by a number of studies is that sociality contributed to this expansion. Recognizing visual cues, such as body or facial gestures, and evaluating these cues within their larger social context requires significant visual processing capacity. 

In “Signals use by leaders in Macaca tonkeana and Macaca mulatta: group-mate recruitment and behaviour monitoring,” the authors examine the interplay between visual cues and coordinated social movements. In primates that live in groups, there are often specific areas designated for a given activity such as foraging or resting. To retain the benefits conferred by performing activities as a social unit, movement between these areas must be done as a group and requires consensus among the individuals composing the group. In this study, Sueur and Petit examine the visual cues utilized by the individual initiating the movement as well as how those cues are modulated based on the members of the group that chose join.

In Tonkean and rhesus macaques, the primate species observed during the study, the individual wishing to initiate a collective movement will begin moving in the desired direction and pauses and back-glances cue other group members of the intent. The authors monitored how the frequency of both these cues affected the actions of fellow group members, and how the number and identity of the joiners affected the behavior of the initiator. In general, pauses and back-glances decreased significantly when the desired individuals joined the initiator in both species. 

The authors grappled with whether pausing was a direct cue to specific group members to join the effort or an expression of uncertainty on the part of the individual initiating the movement. If pausing was an expression of general uncertainty, then pausing should decrease with the number of contemporaries joining the movement regardless of who the joiners were. Interestingly, the authors observed that pausing only decreased when certain members joined the group, suggesting that the pause signal was intended to recruit specific group members to join the action. The only substantive difference noted between species was that Tonkean macaques tended to emphasize recruiting affiliated individuals and rhesus macaques decreased pauses when kin-related individuals joined. The authors hypothesized back-glances were mainly used to monitor the number/identities of the group members joining the collective effort. 

One limitation noted by the authors was the semi-free ranging conditions in which these observations were performed. The distances between individuals was lower and general visibility higher than what would be found in natural populations. Other behavioral factors, such as calls, may play a more significant role in natural conditions. 

This study highlights just one example of how visual indicators contribute to social efforts and facilitate group cohesion. It stands to reason, given the number and variety of activities in which primates take part in a social context, that the expansion of the area of the brain responsible for visual processing observed in primates would provide a selective advantage. While this study alone is insufficient evidence for this proposition, one could imagine how sociality could function as a positive feedback loop driving evolution of regions of the brain that are critical for operating within it. Primates that are more effective at coordinating social activities (ie resource management, group defense, etc.) would lead to fewer individuals being lost to predation or other miscellaneous selective pressures that are more evident in species that can only operate in a solitary capacity. This would, in turn, lead to a more pronounced emphasis on the refinement of inter-individual communication and the physical structures or processes associated with it.

Paper:

Sueur, C. & Petit, O. Signals use by leaders in Macaca tonkeana and Macaca mulatta: Group-mate recruitment and behaviour monitoring. Animal Cognition 13, 239–248 (2010).

In this chapter Katherine MacKinnon and Agustin Fuentes provide a biological and evolutionary context for the discussion of human cognition and niche construction. This context is based on primate studies that shed light on the internal working of primate social life and cognition. By seeing the social organizational and behavioral range exhibited by other primates, it is hoped that the reader would get a better baseline to understand what is uniquely human and what is shared across the taxonomic order. This is spelled out as one of the key questions in the chapter “…how does taking a broader look across the Primate order provides a useful framework for understanding the role of an evolved social cognition?”
 
To better get a sense of the distance at which other primates stand it might be helpful to become familiar with the scientific classification of primates. Humans belong to the genus Homo, the Homini tribe (along with chimpanzees), the Homininae subfamily (along with gorillas), the Hominidae family (along with orangutans) all previous forming “the great apes”, the Simiiformes infraorder (including old and new world monkeys – gibbons, baboons, and spider monkeys) more commonly called just “monkeys”, the Haplorhini suborder (along with tarsiers), and finally the Primates order (along with lemurs). While it should go without saying that humans are not descendants from any of the current primates (but rather humans shared a common ancestor with them), it should be noted that the more proximal two species of primates are in this taxonomic tree, the more genetically similar they are. Therefore, humans are closer genetically to the chimpanzee in their Homini tribe than to orangutans in their Hominidae family. While the chapter provided insight into social and cognitive patters in a variety of different primate species, being aware of this taxonomic can help situate these findings.
 
The framing of the chapter is not simply to learn facts about primate biology or about studies with these groups of primates. Rather, the hope is to develop a framework for understanding evolved capacities found in humans. For example, given that we can see sociality as a pervasive feature of primate evolution present in most primate species, it makes sense to inquire about the type of cognition necessary to successfully live and thrive in a social environment. Then we can ask to what degree this cognitive ability is shared across other species and to what degree it varies across different instances of the same species. This is also a key piece of the framework this chapter hopes to develop. How much variation (of a given biological feature, behavior, or behavioral practice) do you find within and across species? All primates seem to have a large brain in proportion to total body weight (with a convoluted neocortex) however there is also much variation in brain size within the order from the mouse lemur to the modern human. This, to reiterate, would help situate and gain insights from human brain to body ratio.  The socio-ecological variability found across primates provides a powerful lens through which to investigate human evolutionary origins. The authors summarize this perfectly stating: “Ecological pressures, the social landscape, and other elements in an individuals’ life history elicit responses govern by the parameters set by physiology, environment, and experience.” This statement already highlights how flexible and dynamic one’s own understanding of primate evolution needs to be if we are to extract useful lessons to apply to our understanding of humans.
 
The chapter also presents some of the history and chronology of primatology. One of the key pieces of this history is the grounding of human cognition in a Neo-Darwinian theory in the 1970s and 1980s that extended to questions of human morality, aggression, and personality. Another key piece of this history is the shift in theory that comes about with the increase in the number of studies and the number of species studied (from only great apes to hominines). This shifts forces a move away from generalized “primate patterns” to observed a variety of behavioral adaptations. But amongst the biological features shared across primates we find reliance of visual pathways, extended periods of infant-dependency, enlarged brain-to-body size ratio, and sociability and group living.
 
Two specific methodological/theoretical tools for examining primate groups are mentioned: niche construction and social network analysis. Niche construction defined as the modification of the functional relationship between organisms and their environments by altering factors of the environment specifically highlights the complexity of primate evolution brought about by the high degrees of interactions (via feedback loops) between primates and their environment. As expressed in the book, extended period of child rearing brings about different group dynamics that increases predation avoidance. This in turn forces predators to adapt to different pray further reducing pressure of predation, which then allowed for increase niche construction through range exploration, social interactions, and foraging opportunities. Part of the niche of primates includes the social group, which is nested under multiple layers of complexity. Social network analysis is a way to understand this complexity by keeping track of the interactions between individuals, the patterns of their relationships, and the population characteristics of the social niche.
 
One final characterization of the chapter is the discussion about brain growth in particular with its relation sociality. The extended period of dependency characterizes primates from other mammals. A newborn wildebeest would be able to stand and walk just after 7 minutes of being born. It would reach full sexual maturity after only 4 years. This is in stark comparison to newborn humans who would take longer than a year to be able to walk and more than a decade to reach sexual maturity. But it seems to be the ability to navigate through and manipulate the social dynamics of the group what primate brains seem uniquely adapted to do.  The evidence for this is that not just brain volume, specifically neocortex volume, correlates with sociability (not just group size but the complexity of relations). Of particular importance is the mother-infant relationship given that the extended dependency period seen in primates poses a cost primarily to the mother (which in turn might have driven alloparenting).
 
How does all of this inform Neuroanthropology?
 
While the chapter does a lot to balance primatology history, methods, with case examples in its short length, it can seem at times unclear how it contributes to neuroanthropology. For example, it is not clear how we should judge the particular studies referenced in their relevance for understanding human behavior. If some lab experiments are faulty in their design how could we learn to distinguish a valid study with captive primates? What differences would we expect from those studies with primates in the field? To better be able to realize the information that primatology can provide it would also be advantageous to understand the ways in which early Homo (Homo erectus, Homo habilis, etc.) species vary. While all of these species are extinct and do not lend themselves to study like primatology, the discussion about the emergence of bipedalism, the arms race between the pelvic bone and brain size, the use of fire, and the increase in brain size have much to contribute to our understanding of human nervous system evolution. Additionally, there are some (if not many) negative aspects of social human behavior that we can also find reflected in primate evolution. Conflict, aggression, group violence, and infanticide, are all primate behaviors, which vary starkly from chimpanzees to their close cousins bonobos, for example. This comparison shows chimps being more violent and aggressive than bonobos, a violence recognizable in human history.  It would have been interesting to see how it varies across other primates as well.
 
The authors also state in the conclusion that “what we share socially and cognitively, not where we differ, that can inform neuroanthropology.” But it is not clear what is not shared and how to tell the difference. Furthermore, it seems odd to limit the contributions of primatology to neuroanthropology to only shared features. The study of cephalopods (such as the squid and octopus) has much to say about the development of nervous systems in general (but also for the human nervous system) particularly because of how different it is from that of the human. It seems that the chapter’s conclusion leaves an unclear link between primatology and neuroanthropology. While it highlights the importance of how sociality can create feedback loops that fundamentally modify the environment (allowing the extension of caring beyond kin), it remains unclear how this process “…changes the selective equation” in terms of genes and phylogeny (in particular as to how it would affect the primate evolutionary branch of humans). If evolutionary biology is to inform the development of humans, it is not enough to say that some primates evolved the capacity for great sociality, but rather a link must then be made as to how that capacity could have been inherited by modern humans.
 
Questions?
​
What are the first human specific behaviors that come to mind? What are some non-human primate specific behaviors that come to mind? What makes them be one or the other (are they learned or physiological)?
 
What are the ways in which primatology inform Neuroanthropology?
 
The author states “If we remove the exclusivity of neo-Darwinian views of evolution, add the ideas of [developmental systems theory], niche construction, and social and symbolical inheritance and place them in the context of ethnographic knowledge, archeological histories, contingency in human behavior and individual agency, we can derive better anthropological answers.” What are “better anthropological answers”? Better than what? 

In 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:

• Armitage, K.B. Oecologia (1981) 48: 36. https://doi.org/10.1007/BF00346986
• Brooks, K. C., Maia, R., Duffy, J. E., Hultgren, K. M. and Rubenstein, D. R. (2017), Ecological generalism facilitates the evolution of sociality in snapping shrimps. Ecol Lett, 20: 1516-1525. doi:10.1111/ele.12857
• DeCasien, A.R., Williams, S.A., Higham, J.P. (2017), Primate Brain size is predicted by diet but not sociatlity. Nature Ecology and Evolution, 1:112
• Koch, Christof. “Does Size Matter--for Brains?” Scientific American, Springer Nature America, 1 Jan. 2016, www.scientificamerican.com/article/does-size-matter-for-brains/.
  
• Seid M, A, Castillo A, Wcislo W, T: The Allometry of Brain Miniaturization in Ants. Brain Behav Evol (2011); 77:5-13. doi: 10.1159/000322530