by Brian Rivera
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.
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?