J. Turner & A. Maryanski, Origin of Societies by Natural Selection
Living in trees, vision, language, limbs, teeth, brain.. [16 mins.]
In their book On the Origin of Societies by Natural Selection, published in 2008, Jonathan H. Turner and Alexandra Maryanski wrote:
CHAPTER 1
A Brief History of Primate Time on Earth
Descended from the apes! My dear, let us hope that it is not true, but if it is, let us pray that it will not become generally known. —BISHOP OF WORCHESTER’S WIFE AFTER LEARNING ABOUT DARWIN’S THEORY OF EVOLUTION, Circa 1860
MORE THAN 65 million years ago, a small-bodied mammal crawled or clawed its way into the arboreal habitat. This rather unimposing species initiated the primate line that, today, is composed of prosimians, monkeys, apes, and humans. All present-day primates are, of course, the result of evolution by natural selection as it worked on the basic mammalian anatomy over millions of years to make primates ever-more adapted—to trees and, later, for some species of primate, to open-country savanna when the earth grew cooler and the rainforests began to decline. If we are to understand human evolution and the origins of human society, it is necessary to know more about the evolution of primates as selection pressures produced a distinctive anatomy and neuroanatomy. And, notably, in the case of apes, a rather unique set of behavioral propensities and patterns of social structure.
Many social scientists still downplay evolution, preferring instead to believe in what Leda Cosmides and John Tooby (1992) have termed the Standard Social Science Model. The sociological variant of this model goes something like this: Humans evolved like any other animal, but once the brain became sufficiently large to allow for the production and use of culture, such as language and other symbol systems that the capacity for language allows, the explanation for human behavior and social structure must be understood in non-biological terms. True, there may be some basic needs lodged in human biology say, for affiliation, solidarity, power, and other behavioral propensities, but these needs are conditioned and constrained by culture and social structure to such a high extent that emphasis should be on sociocultural rather than biological bases for human behavior and social organization. Individuals learn how to behave through their socialization into a culture or cultures, and their actions are highly constrained by social structure. This kind of “social constructivist” model pervades sociology, and it has become part of a common defense against, if not outright rejection of, any theory or research on the biology of human behavior. To be sure, this model is certainly in the ballpark, but it is simply too extreme. Humans are animals that evolved like all other animals; and despite the spectacular, if not dangerous, cultural systems and social structures that our large brains allow us to construct, these do not obviate the influence of biology on human behavior and social organization, now or in the distant past.
Yet, we do not need to go to the other extreme and argue that culture and social structure are in some direct way caused by biology and, hence, are to be explained largely by biology—a mistake that early sociobiologists once made. But we do need to be attuned to the fact that human biology not only makes human culture and social structure possible (in ways that the Standard Social Science Model argues), but the viability of culture and social structure over the long term is affected by the biology of humans as an evolved primate. There is nothing very radical or extreme in this conclusion because most of the canonized early figures in sociology made similar assertions that some types of sociocultural formations are more in tune with human biology than others. For example, Karl Marx’s concept of alienation, Émile Durkheim’s views on anomie and egoism, Vilfredo Pareto’s analysis of sentiments and derivations, or George Herbert Mead’s views on self, all imply that there are some fundamental needs driven by human biology that culture and social structure can accommodate, or violate. More recently, even anti-science perspectives like postmodernism posit that the emerging “postmodern condition” violates human needs for the anchorage of self in stable groups and culture. What we propose, along with many others who have been willing to consider the biology of culture and social organization, is this: Let us make this relationship between human biology and sociocultural arrangements more explicit and systematic by exploring the ways that biology, social structure, and culture interact.
In this book, we pursue this goal by trying to understand how and why human society originated and evolved. Humans did not construct society in a manner postulated by early social contract philosophers (e.g., Hobbes, Locke, and Rousseau), nor is society only the result of rational choices as is often posited today. Rather, human society evolved from earlier forms of social structure that became unique to apes. For humans are evolved apes, and we carry with us today amidst the grandeur of our sociocultural creations a basic ape anatomy and a set of behavior propensities that we inherited from our hominoid, hominid, and hominin ancestors. The earliest human society—bands of nomadic hunter-gatherers—did not suddenly emerge; with global climatic cooling over time, this simple societal form represented a response to new kinds of problems faced by our hominin ancestors who were forced to leave the arboreal habitat and adapt to the African open grasslands or die. This shift to a savanna ecology posed profound problems for early hominids, who had evolved in a forest ecology with its stable resources and little predation, to confront an open-country habitat with uneven resources and an abundance of large carnivores. Such habitat-related factors would trigger both biological and social evolution with adaptive changes in anatomy, neurobiology, and in social and organizational arrangements.
As we will argue, the very first institutional systems of human societies—kinship, religion, and economy—were not “natural” for an evolved ape with a penchant for a hang-loose forest lifestyle. Indeed, proto-human society represented from its very beginnings an uneasy necessity that often stood in conflict with humans’ ape ancestry. And, as societies developed from their simple hunting-and-gathering formations into ever-more complex sociocultural systems, this tension between our hominoid ancestry and the structures in which humans were forced to exist remained and, indeed, increased. Our view is that we cannot fully understand human behavior and the colossal sociocultural creations that human hominoids have constructed without first appreciating that the ape in us was not extinguished, nor obviated by culture; indeed, our ancestry continues to place pressures on individuals and their sociocultural creations. To understand the nature of this pressure, we need to go back to the beginning and look at our origins. This approach is not just an exercise in ultimate history; it is also an effort to discover what an evolutionary analysis can offer a contemporary sociological analysis of human societies.
Evolution of the Primate Order
The Arboreal Habitat
There are advantages to living in trees. The most important, perhaps, is that compared to an open-country habitat, it is possible to avoid many predators—although eagles, leopards, and slithering snakes can still find you. Indeed, many primate species have evolved distinct alarm calls to alert conspecifics (and other species) that a particular predator is lingering nearby. Another advantage is that a rainforest has plenty of concentrated, year-round foods if a tree-dweller can eat and digest insects, fruits, and plant matter. These advantages are countered by some new liabilities, however.
The most significant disadvantage of an arboreal habitat is its three-dimensional character. The world for most ground-dwelling animals is flat, although obviously there are hills and valleys to traverse. But ground-dwellers rarely confront death by the pull of gravity, unless they are foolish enough to fall off a cliff. The world of tree-dwellers is more precarious because, at any moment, death by gravity can occur. Another liability is that moving about in trees is more difficult as little is level, and it is necessary to maneuver along rounded trunks or, more precariously, across narrow branches of varying strengths. Thus, a terrestrial species taking up an arboreal niche faces formidable challenges if it is to survive and reproduce.
The ancestral species that became the mothers and fathers of all primates surely possessed some useful characteristics on which natural selection could work to make its descendants ever-more able to survive the challenges of the trees. While no consensus exists on the identity of this stem species (although there are several promising candidates), it was a small mammal (as early mammals were all little), without true primate traits but with a generalized body type: four short legs with fingerlike digits on both paws and feet (probably with hindlimb dominant locomotion) that could grasp or claw branches or rounded surfaces such as tree trunks. To travel across tree limbs, it likely possessed a tail (for balance on narrow supports) and had a heightened sense of visual acuity which would allow it to see its way around the branches of trees. However, the dominant sense modality for this pioneer mammal (as is the case for most mammals), was its keen sense of smell. Since smelling one’s way around trees is not a particularly useful orientation in a three-dimensional world, a dramatic shift would occur in the hierarchy of the sense modalities as the primate order gradually evolved. Why would a terrestrial-living, olfactory-dominant mammal take to the trees? Nobody knows, of course, but an arboreal lifestyle has been linked to greater protection from predators and to the opening of a new dietary niche filled with countless insects, sweet fruits, and especially angiosperms (flowering plants), which became a rich food source around the geological timeline that primates evolved.
While the primate stem mammal was not highly intelligent, it was still a mammal, which made it quite intelligent relative to its body size, and moreover, it had the hemispheric brain of all mammals that could be subject to selection for more intelligence. Its brain was wired for emotional responses, some of which are unique to mammals. At the subcortical level, the older centers for fear and defensive anger would be very active, as they are in all mammals. Equally significant, the anterior cingulate gyrus—a layer of semi-neocortical brain that generates play, mother-infant bonding, and the separation cry responses typical of young mammals—were also active and available for selection. Thus, the existence of discrete areas of the brain producing a simple palate of emotions could be subject to further selection if intensifying emotionality had fitness-enhancing consequences. Yet, by living in the trees, neocortical control of emotions was less essential because most predators lived on the ground, thus allowing for the spontaneous and uncontrolled release of emotions without fear of attracting predators.
The Making of True Primates
When natural selection went to work on converting the basic anatomy and neuroanatomy of the stem mammal that took up life in the trees, it established the primate order. The first true primates appear in the fossil record during the Eocene epoch about 55 million years ago. As the nature of human society was both shaped and constrained by the distinctive traits of primates, we need to begin by gaining some insight into what makes the primate order so special and unique.
The Shift to Visual Dominance. The most significant change to mammalian neuroanatomy was a dramatic shift in the dominant sense modality from olfaction to vision. As noted above, most mammals rely upon smell as their dominant sense for object recognition (often scent-marking their environment), with touch (or haptic) and vision subordinated to the sense of smell. A few mammals like bats, dolphins, and whales are more auditory dominant for locating objects in space and use a system of echolocation to move about their habitats and to communicate. Visual dominance is rare among mammals, although many mammals see rather well, as anyone who has thrown a Frisbee for a dog knows (but you also know that a dog still prefers to rely upon its olfactory bulb for environmental cues, sticking its head out the car window not so much to see as to smell what is there).
In contrast … the higher primates (monkeys, apes, and humans) are endowed with “extreme morphological specializations for high visual acuity.” For natural selection to make the primate visual system dominant, it was necessary to change the juxtaposition of the eyes, by rotating the eye sockets to the front of the face so that the slightly different images viewed separately by each eye overlap and combine, thereby creating the “stereoscopic effect” of solidity or depth perception. To protect the eye, selection also favored a full-post orbital bar (a bony ring) to enclose the eye sockets. It also enhanced primate acuity with a retinal fovea (to see details close-up) and color vision which greatly increased the capacity to identify foods and other objects in a three-dimensional environment. In fact, the higher primates (monkeys, apes, and humans) are unique among placental mammals in their sensory ability for very fine-tuned color discrimination.
In order for vision to become the dominant sense modality, however, the brain also had to be rewired so that sensory conflict among visual, haptic (touch), auditory, and to a lesser extent, smell, would not occur. Where the parietal (haptic), occipital (vision), and temporal (auditory) lobes meet are a series of association cortices, such as the inferior parietal lobe; these association cortices do the work of subordinating touch and sound to vision. The olfactory bulb is subcortical, sitting at the front of the brain below the prefrontal cortex; and while smell is not under direct control by the neocortex, it is dramatically reduced in primates and hence not likely to work at cross purposes with vision. Moreover, if a primate smells something that arouses its interest, it will turn to find the object visually, just as it does for anything that it hears or feels.
This subordination of other senses to the visual thus involved very complex changes in primate neuroanatomy; and for such changes to occur, there must have been intense selection pressures for visual dominance. Visual acuity has obvious value in trees because an animal can readily access the weight-bearing potential of limbs, as well as see where it is going on thick-leaved, curving branches. Moreover, if it is necessary to leap from branch to branch, stereoscopic and color vision is clearly fitness enhancing. We need only imagine an olfactory-dominant primate using its sense of smell to guide movements across narrow, swaying branches to appreciate why all higher primates became visually dominant. …
… [The] creation of the association cortices integrating the sense modalities under vision had another long-term consequence for hominid and human evolution: the capacity for language. As is now well-established, chimpanzees and other great apes (gorillas and orangutans) can use non-auditory ways to communicate with language (via sign language or use of pictograms connected to a computer). While an ape’s vocal tract (the distance between the lips and vocal cords) is similar in morphology to humans and works in the same way, their lips, tongue, larynx, and muscles coordinating these areas are not set up for “talk.” Yet, the neurological apparatus of chimpanzees is so elaborate that when a young ape is socialized in a human speech environment, it is able to comprehend both English words and complete sentences at about the level of a normal three-year-old human child. Why is this so? One answer is that in rewiring the brain for visual dominance, another capacity was created, if the neocortex grew to sufficient size (as it did in apes but not in monkeys). This capacity was not created for human language, per se, but represents what is called a pre-adaptation that has evolved for other reasons (in this case, visual dominance). Yet, once in place, this trait then can be subject to subsequent selection to generate other fitness-enhancing traits (in the case of humans, language). Thus, as the brain was rewired for visual dominance, something else was conditionally piggybacked onto this new wiring: the basic neurological capacity for language. With selection on this capacity, culture and human society became possible.
A visually oriented primate experiences the world very differently compared to other mammals. When a non-visual sensory mode is activated by an environmental stimulus, primates immediately turn to see the object or event that has drawn their attention. The combined sensory inputs are then then integrated to form an impression of what the object is, and this integration will be dominated by visual processing, with haptic, auditory, and olfactory senses adding information to be coordinated with vision. Once the anatomy and neuroanatomy are rewired for visual dominance, a primate relies on this modality both for object recognition and as a communication channel. Even humans who use their auditory system for most communication tasks rely heavily upon their visual system to interpret body gestures in face-to-face encounters. And, when confronted with “mixed messages” stemming from conflicting, simultaneous verbal and visual communication, most humans subconsciously place trust in their visual sense to correctly “read the situation” by making eye contact and interpreting facial expressions. This is the case for all higher primates, including humans, who respond to each other visually by reading gestures of face and body. This holds true for most other objects in the environment; they are literally “visualized” with sensory inputs subordinated to the visual. This shift in the relative power of sense modalities had, and still has, large effects on the nature of human social relations. Thus, a critical step towards human society was taken as evolutionary forces produced this shift to visual dominance, although the full potential of this shift in rewiring the brain, which laid the foundation for language and eventually culture, did not emerge until a few hundred-thousand years ago.
The Primate Body. Natural selection also reshaped the stem proto-primate to generate the primate order. The four limbs and flexible digits were retained but adapted for greater movement in trees. The limbs of all primates are more generalized and flexible than those in other mammals, making it easier to move about on uneven surfaces. Equally significant, natural selection made the pads on the feet and (what became) hands more sensitive at the nerve endings, thereby enhancing the ability to feel the texture and strength of branches. To protect the sensitive fingertips, the mammalian claw was replaced by flattened nails on the digits. And opposable thumbs and toes were evolved for a tighter grip on objects and for swinging across branches. The wrist and shoulder joints of primates are also much stronger and more flexible than in other mammals. These generalized characteristics allowed primates to easily move about the forest canopy and the forest floor. And later, these traits allowed some primates to move into terrestrial habitats, although this movement to a wide-open terrestrial habitat teeming with predators posed real dangers for an order of mammals built for life in trees.
Dentition also underwent modification and became more generalized, allowing primates to eat an omnivore diet of fruits, leaves, roots, plant matter, tree gums, flowers, and occasionally animal protein in the form of insects and small mammals. Such changes in the teeth, jaws, and muscles for chewing made primates the “jacks of all trades” in their foraging habits—a fitness-enhancing strategy enabling them to consume a larger variety of foods in diverse habitats.
Growth of the Brain. One of the hallmarks of primate evolution was the expansion and increased complexity of the brain. The primate brain was not only rewired for visual dominance, it was also altered to make primates more intelligent than most mammals. Brain size in mammals is roughly correlated with body mass, and so the relative size of the brain is measured against body size. In rough terms, brain size is also correlated with levels of intelligence; and so, controlling for body size, the higher primates (monkeys, apes, and humans) have the largest brains of all animals and, hence, are the most intelligent. An increase in brain volume (with a notable expansion in the visual, tactile, and sensory association areas of the neocortex) would be adaptive for tree-dwellers on many fronts but, in particular, it would enhance survival and reproductive success in a three-dimensional environment by enabling rational “cortical-based” calculations on the strength and distance of branches, as well as the safest routes through the trees. …
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The Source has been:
Jonathan H. Turner and Alexandra Maryanski, On the Origin of Societies by Natural Selection (Studies in Comparative Social Science), Routledge 2008
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