Dunbar et al. Archeological basis for Social Brain Hypothesis
Coevolutionary cognitions of materials and emotions enabled larger group sizes..
The Source:
Clive Gamble, John Gowlett and Robin Dunbar, ‘The Social Brain and the Shape of the Palaeolithic’ [British Academy Centenary Research Project], in Cambridge Archaeological Journal 21:1, 115–35, 2011
[dict. Encephalization: evolutionary increase in the complexity or relative size of the brain, involving a shift of function from non-cortical parts of the brain to the cortex.]
Stage and gradient: the shape of the Palaeolithic as deep history
… Here, we explore the relationship between [Dunbar’s] social brain hypothesis (SBH) … encephalization [and] the emotional bases of social life and the archaeological data.
We argue that a coherent exposition can only proceed by examining the material and emotional resources which underpin social interaction. These have not been considered before by archaeologists since they lie outside traditional concerns and structures of inference. The exploration presented here consists of a review of relevant data organized in three temporal movements, with particular attention paid to a disconnect between the cognitive and material evidence 1.5 Ma–400 ka years ago.
[Ma = 1 million years, ka = 1000 years]
Social complexity and encephalization
For many years, scholars have sought to explain the particular and unusual characteristics of human evolution; among which our extraordinary encephalization ranks highly. Most hypotheses, however, have tended to assume the benefits of a large brain, taking it as self-justifying. In contrast, the social brain hypothesis (SBH) approaches the issues analytically and comparatively, recognizing that the evolution of a large and expensive brain would need to be driven by strong evolutionary pressures.
The hypothesis that hominin social lives drove encephalization derives from the observation that a very close link exists between the intense social lives of primates and their large brains, expressed by a strong correlation between community size and neocortex size. Furthermore, it is only amongst primates, including humans, that a quantitative relationship exists between social group size and relative brain size. It is therefore suggested that this relationship must also have held for hominins and that it can be tested archaeologically.
The essence of the SBH is that, in order to survive, all species have to solve certain core ecological problems (in the case of primates, principally predation risk), and that primates do this socially rather than by individual trial-and-error learning.
The SBH has now been extensively tested against alternative hypotheses, and has consistently been shown to be the only functional explanation for brain evolution within the primates. Indeed, a more detailed path analysis has demonstrated that most of the alternative explanations, which typically focus on ecological and life-history variables, are constraints that need to be solved in order to allow brain size to increase for social reasons. …
… In the case of modern humans, as for chimpanzees, social group here refers to the community rather than the overnight camp or band, or any of the other layers in the extended social network identified …
Although the social brain hypothesis has commonly been viewed as a statement about social group size, it is important to emphasize that, in fact, the hypothesis is about social complexity.
Community size is an emergent property of that underlying complexity — if only because the number of dyads [two elements] and triads [three elements] increases proportionally as total group size increases [e.g. ‘family’ units].
A key issue here may be that dispersed social systems in which some members are encountered only infrequently may be especially demanding cognitively, because at any given moment virtual group members (i.e. those not physically present) have to be factored into the calculations about the relationships and behaviour of the individuals with whom one happens to be at that particular time. The implications of the social brain hypothesis are therefore that larger communities create problems for integrating the various social layers, such that managing interaction adds significantly to cognitive load. While earlier hominins may have had fewer levels to integrate, their ability to manage cognitive load will always have impacted on other adaptive constraints such as fission and fusion. …
Several fundamental questions emerge from this discussion of social complexity. First, if the structure of these grouping layers remains proportional as community size increases, what are the implications for the size and structure of hominin communities and their constituent sub-units? Second, what implications do these have for the structure of social relationships (kinship, friendships, alliances) and the way these are regulated, both formally in terms of rituals and obligations, and informally in terms of personal interactions? Third, when and why does language become essential, and is its substantive function to facilitate the production of technology or social integration?
These issues, in turn, have implications for the evolution of advanced social cognitive competencies such as theory of mind and the higher orders of intentionality, sometimes referred to as mentalizing or mind-reading (the ability to understand another individual’s mind states) that in living animals appear to be unique to humans. Mentalizing is the ability to understand, or have beliefs about, the mental states of other individuals, and it forms a recursive hierarchy of levels known as the orders of intentionality. This begins with first-order intentionality (the capacity to have a belief, or to know that something is the case), a state that is probably common to all mammals and birds. Second-order intentionality (the capacity to have a belief about someone else’s belief) is acquired by humans at about age 4–5 years, and is a trait that, if shared with any other animals, is probably shared only with great apes, and hence would, in all likelihood, have been shared by all australopithecines. Modern humans seem to have an upper limit on their social cognitive capacities at fifth-order intentionality. The higher orders beyond level two are, among living animals, unique to humans, and must have been acquired successively over the time span of the genus Homo. Presumably, the technical, social and cultural differences between ourselves and other members of the animal kingdom must be related to these differences in cognitive function.
These capacities are intimately related to our ability to engage with the world of the imagination, and seem to be crucial to our ability to indulge in story-telling, religion and even science. Second-order intentionality (formal theory of mind) is minimally necessary to allow us to step back far enough from the world to be able to ask how and why it could be the way it is. Without being able to ask this question, we could not imagine that the world might be otherwise than as we actually find it; as a result, we would not be able to construct the fantasy worlds of story-telling or organize our social arrangements into the purely conceptual structures such as kinship that make it possible for us to coordinate our societies. Although the rise of cognitive archaeology [ref. Renfrew] has played a significant role in introducing the concepts of cognitive psychology into the discipline during the last decade, this has tended to focus mainly on mainstream instrumental cognition. The implications of social cognition as such have yet to be explored.
Asking questions about cognition has important implications for our understanding of human evolution. To what extent, for example, is the ability to detach oneself from the immediacies of the physical world (a requirement for the basic level theory of mind or second-order intentionality — minimally needed to operate effectively in a human social world) necessary to be able to visualize the end product of a tool in the raw material of a core? Indeed, this capacity to detach oneself from the immediacy of the world is, in all probability, necessary to construct tools designed to facilitate the extraction of resources. And if, minimally, only second-order intentionality is needed for tool manufacture, what is it that we do with the higher orders, given that they seem to be neurally (and hence energetically) very expensive to maintain? Since social cognition can be viewed as a hierarchical sequence of mentalizing states, exactly when did the different levels come into play and how did they limit what could be done?
Therefore, explaining major aspects of human evolution through the social brain is not for us an exercise in biological reductionism. Rather, we assert that explanations have to work at all levels…
Drivers and amplifiers of change
… we identify a pathway that leads from evolutionary drivers to social complexity via four closely interlinked components: cognition, forms, materials and emotion … to investigate how amplification resulted in change. Our emphasis on amplification addresses the timetable of when, and the question of how, change happened. …
… The conventional strategy has been to move directly between social cognition and social forms to infer, for example, what new adaptations would be needed to support an evolved Theory of Mind or what the acquisition of language would solve with regard to cognitive load. Up until now this approach has largely by-passed the archaeological evidence.
What is distinctive in [our approach] is the introduction of materials and emotions as the core of resources around which hominin social lives have always been scaffolded. Materials and emotions provide the proximate means to negotiate and modify social interaction and as such underpin all hominid and hominin societies. They are the basis of the ‘bonds that bind’. Their prominence in the model recognizes that human cognition is distributed, involving a co-evolutionary relationship between people and things. Therefore, it is not possible to identify simple correlations between a change in social cognition and the forms it took, or to account for biological and cultural solutions by new adaptive circumstances. The co-evolutionary process outlined here cautions against such simple cause and effect relationships when it comes to social and technological competences. The reason is that in hominin systems of distributed cognition, materials and emotions have always filtered evolutionary changes driven by either environmental or sexual selection.
Social and technological competencies
… By technological competencies we refer to the skills of hominins to turn materials into mechanisms that facilitated larger community sizes. The domestication of plants and animals is an obvious example from late in the story; an earlier example would be the way innovations such as hafted projectiles [e.g. knife, axe, or spear with a handle] increased yields. Technological competence also extends to symbolic artefacts that have the purpose of encoding information to make larger social networks possible. These competencies are subsumed under social forms … Archaeologists have devoted much effort to timetabling the appearance of such competencies and inferring from them changes in hominin and human behaviour.
Social competencies cover a wide range of complementary skills that deal with issues such as integration, negotiation and categorization of individuals, groups and communities. … [Dwight Read] argues that the shift from experiential to relational-based forms of social organization was the key transition in human evolution. Experience can produce significant social categories such as aggressive males, in contexts where support is uncertain for those interacting with them. With the move to the conceptual production of relations, social integration is no longer determined solely by the epiphenomenon of experientially-based social interaction. It moves instead to a pattern of social trust based on … sanctioned predictability.
The result has been expanded fission-fusion, systems of kinship and marriage and extended absence from groups and communities. These have traditionally been areas where the lack of obvious archaeological proxies has led to their neglect. Many social competencies draw on emotions for their inspiration …
The distinction we draw here between these two [social and technological] competencies is perhaps too stark. But it demonstrates well how proxies are used in the big picture of human evolution. Instead of either competence leading the way towards an explanation, they work in tandem as co-evolutionary partners in a system of mutual influence. The social brain model does not prioritize any one of these explanatory schemes over any other. Rather, it recognizes that the model for evolutionary change … deals in multiple pathways, as will now be explored.
Dividing the continuum
The long sweep of human evolution has to be divided for effective analysis. Here we refer to our divisions as ‘Movements’ to avoid the conceptual baggage that comes with labels such as period, stage or transition. Movement used in a musical sense provides an appropriate metaphor for the shape of the Palaeolithic: its use underscores both continuity and development where themes are repeated and new elements introduced during its course as the tempo changes. … Here we use movements to examine the evolution of social complexity.
… When applied to the continuum of the hominin past since the appearance of stone technology we arrive at the following three broad movements.
The evolution of Homo, c. 2.6–1.6 Ma with a focus on 2.3 Ma, when Homo rudolfensis and Homo ergaster brain size indicates that the primate limit to social complexity had been exceeded and with encephalization some 50 per cent higher than in the australopithecines. Community sizes of around 50 are found among chimpanzees and other social primates (e.g. baboons) [indicating] that this was the upper limit for small-brained Australopithecines. During this movement community size for Homo expanded to 100.
The appearance of large-brained hominins, 1.5–0.4 Ma with a focus on 0.6–0.4 Ma, when large-brained hominins including late Homo erectus, Homo antecessor and Homo heidelbergensis point to community sizes of between 100–120.
Global distribution and population increase, 300– 25 ka with a focus on 60–40 ka, when encephalization after 400 ka predicts community sizes of 120–150 for both Homo neanderthalensis and Homo sapiens. The focus of this movement is the commencement of Homo sapiens’ global population dispersal.
Three movements
Emotion, intentionality and even society are terms that most Palaeolithic archaeologists either ignore or treat cautiously. They study materials, but rarely with an aesthetic approach where the sensory properties are given as much importance as their utility in cutting and pounding.
Here we use the SBH to examine alternative information from familiar archaeological evidence in order to examine the evolution of social and technological competencies and, by so doing, to better understand the process of amplification that led to complexity.
The first movement: the evolution of Homo c. 2.6–1.6 Ma
The move to bipedalism, an essential element of the hominin body form, was completed before the earliest appearance of stone tools at 2.5 Ma. It is also the case that climate became both drier and cooler in the Early Pleistocene (GSA timescale now sets the base of the Pleistocene at 2.558 Ma), possibly triggered by tectonic uplift in the Tibetan plateau that resulted in greater correspondence between the East Asian and Indian monsoons, although significant northern hemisphere glaciation had not yet commenced.
The appearance of Homo with brain sizes in the range 600–900 cm3 is dated to around 2.4 Ma with finds of Homo rudolfensis, and then of Homo habilis. Further species of small-brain hominin include Homo georgicus in Asia, slightly older than larger-brained examples of Homo ergaster in Africa and Homo erectus from Asia.
A significant feature of the first movement is captured by the Out of Africa 1 model. Currently, no australopithecines have been found outside Africa suggesting that Homo expanded into other parts of the Old World with a flake and simple core stone technology … [and] for the moment the earliest history of Homo is best seen in Africa. Low-latitude savannahs and bushlands with seasonal water regimes that affected both prey and plant abundance are currently the best known …
Material
The importance of meat in the diet of early Homo has been widely discussed in the taphonomic debates of the last 30 years. Hominins were very familiar with this material and inferences of hunting and scavenging have been based on the evidence of cut-marks and bone breakage. While the methods used to acquire meat, marrow and fat are important because they impact on dietary security and raise issues of sharing, reciprocity and social bargaining, the most important demonstration from a social-brain perspective is that a shift to higher-quality foods had taken place. Such a move … was a consequence not only of the energy demands of larger brains but also corresponding reduction in gut length and hence its processing power. Therefore meat and animal protein generally formed a novel material … and … [show] these early hominins occupied a broad array of habitats with a diversity of [meat and plant] high-energy resources. However, not all of these food materials were readily accessible to a small-gut hominin and required the evolution of social and technological competencies.
For example, it has been proposed that fire for cooking would facilitate encephalization, gut reduction and the move to animal protein. Roasting meat breaks down protein and starch molecules making them more digestible and so acts as an external stomach that would have compensated for the trade-off in the size of expensive tissues between gut and brain. However, evidence for fire in the first movement is still restricted, although intimately associated with hominin activities and roasting in hearths is not seen until the last half million years, beginning in the second movement.
Currently the earliest stone tools are 2.5 Ma old from Gona in Ethiopia, while cut- marked bones from Dikika, Ethiopia, show that stone technology was used by Australopithecus afarensis 3.39 Ma years ago. Tool manufacture and use by the African great apes and New World monkeys suggests that the antiquity of tool use could be a much older phylogenetic trait in hominids. While often regarded as flakes and hammers produced by simple percussion, studies of 2.3 Ma Oldowan assemblages from Omo have revealed more complex conceptual patterns and an understanding of the properties of stone far removed from an anvil-on-anvil interpretation of [earlier] Oldowan technology. In particular, the hominin knappers [stones shaped by striking to make tool or weapons] displayed rational reduction choices through the sequential planning and understanding of core geometry. Stone was associated with meat and bone, as shown by cut-marks, and with wood …
The greater complexity of even earliest hominin stone technology is also revealed by raw materials. When faced by a choice of different stones, the hominins at Gona deliberately selected particular raw materials to make their tool. This appreciation of materials applied to those in the immediate vicinity of these hominins, but after 2 Ma stone raw material was transported over distances greater than 1 km and by 1.6 Ma this reached 13 km … [and] the sheer quantities of stone on some sites speak for the extent of shared endeavour in hominin behaviour.
The picture that now emerges of the appreciation and use of the properties of stone from 2.6–1.6 Ma is far more sophisticated than previously believed. This is clearly shown by the use of a prepared core technology (PCT) that is present in some form in the earliest assemblages, although once thought to appear only with the much later Levallois technique. These oldest stone materials are now closer to the conceptual frameworks of later large-brained hominins and much further away from the percussive stone tool-making abilities of chimpanzees with which they were once compared.
Emotions
The use of materials outlined above points to social interaction that concentrated on what was immediate in the hominins’ environment. At a larger social and spatial scale, there would have been pressure from the location of resources to redistribute sub-units within the expanded communities of hominins which the SBH predicts (c. 70–100 individuals). On larger landscapes with fluctuating resources, a more flexible organization would have been a necessity. Moreover, the dynamics of such fission and fusion created challenges for social interaction that presented selective pressures for communication and the ability to handle the higher cognitive load associated with larger communities. During the first movement, the trend to colder, drier climates would have increased these selective pressures through potentially longer periods of fission in search of scattered resources and fusion around key resources such as seasonal waterholes.
The distributed cognition of these hominins is amply demonstrated by their involvement with a range of materials, stone, bone and meat as well as those we can assume they came into contact with such as water, plants, the ground they walked on and perhaps the trees they slept in. In other words, the core of social life involving the interdependence of materials and the affective response to their properties was present and well developed, as their PCT [prepared core technology] shows.
Besides materials, hominins had their emotions with which to forge social bonds. The lack of suitable archaeological proxies for emotions has led to their neglect in human evolution. However, we can infer from the limited evidence for contact distances beyond a day’s foraging that the creation of social bonds was achieved through regular face-to-face interaction among local sub-units that were subject to periodic fission–fusion.
Social grooming remained physical, producing strong emotional responses that created and confirmed bonds between individuals. Furthermore, the encephalization of these hominins strongly suggests they had reached at least level 2 intentionality (see above). In this they would recognize the feelings of those with whom they interacted, and appreciate that they did not necessarily share the same perspective. The extent of such sharing and common interests had to be evaluated through the outcomes of social activities based on conceptual relationships rather than simply categories of experience. Here, the sequential planning of PCT [prepared core technology] and the selection of specific stones provided those tests for a hominin Theory of Mind since they made explicit the relationship between materials, emotions and other hominins.
There is little here to suggest the amplification of hominin emotions to meet the challenges of social complexity, larger communities and greater cognitive load. However, amplification had occurred through their involvement with materials, in the manner described above, and for which archaeological proxies such as stones exist. We suggest that amplification of materials in the core of social resources was sufficient for this movement to larger community size and greater encephalization to proceed. This was not independent from emotions but rather a co-evolutionary process where a greater involvement with materials played a leading role in adapting to a selective pressure.
Finally, the first movement emphasizes the varied use of archaeological proxies to support an evolutionary argument. If social competencies drove the movement to larger community size, then greater fission and fusion explains longer raw material transport. There is, however, only limited evidence for such transfers in the first movement. Hence stone tools, as an instance of how materials were elaborated into social forms, remains a more persuasive interpretation of the proxy data as an example of amplification. However, another interpretation might give equal weight to social and technological competencies and, in this example, factors such as group defense and social competition would provide selection pressures for a change to stone tools and vice versa. It is therefore important to acknowledge that evolutionary pathways are always multiple rather than to strictly interpret the proxy data in a linear fashion to support a preferred option.
The second movement: the appearance of large-brained hominins c. 1.5–0.4 Ma
This movement has two distinct phases. It begins with innovation in stone technology in the form of large cutting tools (LCT): bifaces [stone implement flaked on both faces], cleavers and picks made on large flakes.
But following these innovative instruments, there is little further change until 0.8 Ma. However, during this plateau of technological innovation, hominins achieved full bipedalism as shown 1.5 Ma years ago by the Ileret footprints, while the contemporary Nariokotome boy from East Turkana exhibits a fully evolved hominin body form and a brain of 880 cm3.
The later phase sees the appearance of large- brained Homo that represents a significant increase in encephalization. But, on this timescale, such increases were the culmination of a slow gradient … Estimates of group size using archaeological data … strongly suggests that increases in community size of up to 120 postdated this 0.5 Ma Homo heidelbergensis locale and so came late in the second movement.
The 0.6–0.4 Ma focus in the second movement is marked by greater amplitude and duration in the climate cycles of the Middle Pleistocene [Sahara and Arabia] …
… Throughout the second movement, hominins were an Old World species. They inhabited more of this landmass than in Movement 1, as shown for example in the earliest occupation of Spain at 1.2 Ma and latitude 52°N in the British Isles by 700 ka. In Europe [there are] postulated two colonization phases: before 0.6 Ma with thinly spread occupation in southern Europe and ‘visitors’ in the north of the continent, and after 0.6 Ma more permanent occupation throughout the continent.
The limits of their occupation in East and Central Asia are less well known, but they extended as far north as the extreme seasonal conditions of Siberia and the high-altitude plateaux of Mongolia and Tibet allowed. While these environments would have had the resources to support hominins, at least during favourable parts of the glacial–interglacial cycle, it is likely that the impact of such seasonality on fission–fusion presented insuperable challenges to integrating sub-units into larger communities and regional populations.
Above all, the second movement raises the issue of a mismatch between the expectations that larger social communities would be paralleled by innovations in materials, concepts and social forms, not to mention geographical expansion. …
Materials
The mismatch is, however, more apparent than real. There are a number of innovations associated with the use of materials. Stone technology sees a significant conceptual development in the imposition of a long axis on tool forms as well as knapping large flakes. In constructing form around the axis, the makers show an ability to control several variables almost simultaneously, within a framework of sequential operation which serves to reduce cognitive load. This management of four or five variables requires a level of processing (a mind’s-eye view) perhaps closely similar to that required in high levels of socially-orientated intentionality.
These biface [stone implement flaked on both faces] technologies (LCT) covered much of the hominins’ Old World distribution and were made either on large flakes or on nodules, particularly flint. Furthermore, this innovation is matched at times by greater symmetry in tool forms, particularly among Acheulean bifaces. Such symmetry has attracted comment from a cognitive perspective as well as interpretations of sexual selection and has been compared to the attention skills found in strong emotional bonding between dyads [consisting of two elements e.g. mother-child].
Contexts also became more varied. For example, the symmetrical, single reddish-brown quartzite biface is, to date, the only artefact found with the c. 600-ka-old Sima de los Huesos hominins. Its placement among the bodies suggests an appreciation of colour as well as form and by its very distinctiveness is regarded as a symbolic artefact possibly equivalent to a grave-good. The repeated discard of ovate bifaces took place at the 500 ka locale of Boxgrove, and in particular around a waterhole feature. The structured character of this activity is regarded … as a social mechanism by which individual actions contributed to increased group cohesion and flexibility.
This phase is also notable for the appearance of flaked bone tools. These are known from Olduvai Bed II, while much later bone bifaces are relatively common at some European locales. Wood working is a feature of this movement too, beginning with the polished plank at Gesher-Benot-Ya’aqov, 780 ka and the 400-ka-old spears at Schöningen and Clacton. Schöningen has a range of worked pieces including a fire charred ‘spit’ or stave and several pieces with end-notches probably intended for hafting stone flakes. The rarity of bifaces to the east of the long-established Movius line in Asia has led to suggestions of a bamboo-based technology whose properties as a container for liquids and a source of instruments in the form of knives and darts. This hypothesis remains plausible although numbers of artefacts including bifaces are increasing in the region.
Evidence for composite concepts is also compelling in evidence for the control of fire at locales such as Gesher-Benot-Ya’aqov, the Taman peninsula, and later at Beeches Pit, Schöningen and Qesem Cave. The large hearths in particular, as found at Beeches Pit and Schöningen, demonstrate significant scales of resourcing — movements of 50 or 100 kg of wood — and indicate aspects of division of labour and forward planning. They represent essentially a shared technology. These hearths bring together a number of materials (fuel, plants, nuts and meat as well as hominins) and transform them into cooked food, burnt ground and places for social interaction.
At any place north of 40°N, hominins would encounter a significant deficit of daylight hours in winter. Modern humans are almost invariant in their sleep-time at any latitude, indicating the great extent to which fire-lit time has substituted for natural light as a social-technical mechanism. The same can be postulated for the Neanderthals: given their heavy dependence on a meat diet, and the time and resources necessary for cooking large animals, fireside time would have been vital for them.
These hearths are indeed also accompanied by evidence for hunting herd animals, such as horses at Schöningen, while elsewhere in non-hearth locales such as Boxgrove a range of archaeological evidence points to the effective hunting of single large mammals (rhinoceros and elephant respectively). Stable-isotope data are poor for this movement, but among northern hominins the expectation would be for a preponderance of meat in the diet as predicted by the degree of encephalization, while roasting technologies would have played an important role in exploiting highly productive underground storage organs in low latitudes.
The role of raw material in conditioning the shape of artefacts, especially ovate and pointed bifaces has received attention. The flaking properties of different local stone materials — quartz, quartzite, flint, basalt — were appreciated across a (LCT) [large cutting tools] world that extended from South Africa to England and India. Meanwhile, simpler industries continued further East beyond the Movius line, although not exclusively so. Raw-material sources still indicate a predominantly local pattern with very little being transported beyond 20 km from its occurrence in the landscape. However, in marked contrast to Movement 1, all regions with LCT have evidence for a few instances of distances up to 100 km which indicates augmentation of spatial scale irrespective of latitude and ecology.
Emotions
With predicted community sizes of up to 120, we should expect selection for mechanisms to amplify the emotional basis by which lasting social bonds were forged. One selection pressure for this is clear. With larger community sizes less time was spent together as dictated by fission and fusion to balance population to resources.
Furthermore, the effect of the long-term trend to colder and drier conditions would increase seasonality and further extend fission–fusion by which hominins adapted to the changing ecology.
The alternative would be to inhabit only those environments which had a density and reliability of resources that kept the intensity of interaction at established levels. But even so the increased numbers in the community placed pressure on existing methods of social interaction such as physical grooming.
Two responses to this pressure have been suggested which would have amplified the emotional content and context of interaction that sustained and defined social bonds. The first … was selection for language as a means to integrate larger numbers and to augment physical with vocal grooming. This new form of integration was advantageous when it came to balancing the hominin time budget for interaction, finding and consuming food, travelling and sleeping. A second suggestion is the use of controlled fire, which becomes common during the late focus of the second movement. [It has been] shown how fire extends the hominin day while also providing an affective context in which to interact socially. If, as seems probable, these two social forms, language and fire co-evolved then they serve as an example of how amplification occurred by simultaneously drawing on materials and emotions from the core of social resources.
However, these were not the only social forms to emerge as solutions to the problem of how to integrate more sub-units into a larger community. Music, which can be made without instruments, is one obvious means by which the emotional strength of interaction between individuals can be enhanced through chanting and related practices involving dance and performance. In this case, the hominin body is its own proxy for the production of musical sound, while the patterns at archaeological locales such as Bilzingsleben suggest they involved more complex performances at hominin gatherings than simply the activities of animal butchery and stone knapping.
Music may well have preceded language both as a means of communication and as a way of amplify- ing emotions during social interaction. … And this is where a social-brain perspective provides a framework to go beyond speculation and establish the links between emotion and materials, some of which may produce durable proxies. The evolutionary question is how these resources were drawn on together to solve problems of cognitive load that arose from social interaction in larger communities.
Hominin emotions … were under selection to support stronger social ties since this is how complex social life evolves. An important connection to make is therefore between those higher levels of intentionality and the amplification and modulation of emotion. Higher levels of intentionality did not make hominins mind-readers, but the higher levels of intentionality would need to embrace an awareness of others’ emotional states. In other words, hominins had to become aware of conceptual emotional states that formed the basis for managing social relations.
Emotions are notoriously difficult to describe and classify, but a useful distinction can be drawn between the primary emotions that all animals have — fear, anger, happiness, sadness, disgust, surprise — and which do not require a theory of mind since they have basic survival value, and second-order, or social, emotions such as guilt, remorse, greed and shame that do need a theory of mind to carry social weight. Social emotions arise only in someone who possesses, minimally, theory of mind and level 2 intentionality. This is because the individual needs to recognize another person’s point of view, especially if that person is not present yet still influencing social conduct. This distinction is comparable to [a] transition from experiential to relational-based forms of social organization. Such advanced emotions are relational concepts that act as moral devices to control the actions of individuals and groups and organize behaviour that can take place away from others. Of course, such devices can be ignored, but as all free-riders know the penalties for being caught can often far outweigh the temporary benefits of breaking the rules. For species as deeply dependent on sociality for their survival as hominins, social exclusion can have devastating consequences for an individual’s survival.
The second movement might therefore appear to present a chronological mismatch between brain and community size and the response, as measured archaeologically, in terms of new social forms especially innovations in material culture. Or, at least that is the story which the archaeological proxies appear to tell. However, this timetabling mismatch tells us more about our expectations and dependence on traditional proxies than about the pattern of human evolution.
Instead, we argue here that the second movement saw some innovations in terms of materials but above all in emotions. The co-evolutionary partners, materials and emotions, do not have to work in equivalent ways as our earlier discussion of social and technological competencies indicated. Indeed, the lack of innovation in materials could indicate that in the second movement the emotions were the resource most subject to selection for amplification. This outcome was expressed through mechanisms such as music, performance, language and codes of conduct employing second-order, social, emotions.
Movement 2 therefore differed in terms of the evolutionary response to encephalization by amplifying emotional resources in novel ways to cope with factors, such as cognitive load, arising from greater social complexity.
By contrast, in movement 1 materials played a more significant role in the process of amplifying the basis of social bonds.
The third movement: global distribution and population increase 300–25 ka
This movement also has two sections. It begins with a steady addition of technological innovations, many first observed in Africa, and then during the focus of 60–40 ka a marked increase, particularly in Europe and western Asia, in the quantity and diversity of seemingly novel materials and material culture. This late focus has attracted much attention as evidence for a human revolution in culture and cognition allied with a major geographical expansion.
With the exception of Homo floresiensis, the trend to large-brained hominins continued during the third movement. Predicted community sizes for Homo sapiens and Homo neanderthalensis were in excess of 120 and with an upper limit of 150, twice that of primates and australopithecines.
The climate record during this movement has been used to provide a background to the anatomical and genetic evidence for an Out of Africa 2 dispersal by Homo sapiens. The timing of this population event is still unclear. It has been linked to [climate change] with a presumed, but undemonstrated impact on Asian hominins and conditions which resulted in a population bottleneck for African Homo sapiens. Such bottlenecks are indicated by the genetic data but, apart from ‘molecular clock’ estimates, remain undated by independent scientific methods. The presence of a similar bottleneck in Neanderthals would suggest that the causal events took place at a much earlier date. Instead, the arrival of Homo sapiens in Australia at least by 50 ka forms a benchmark from which the date of the African dispersal, as shown genetically, is estimated.
The Australian evidence also points to a major feature of the third movement, and one that continues after our time frame closes at 25 ka, namely global colonization by a single hominin species. This pattern of dispersal into previously unoccupied continents and oceans was not instantaneous but formed a gradient of population dispersal that began, as indicated by archaeological evidence for the Aterian, as early as 120 ka when a humid corridor existed through the Sahara. In southern Africa, two pulses of dispersal … occurred between 80–60 ka. The pace then accelerated with the crossing of the Wallace line to Sahul 50 ka ago and continued until the arrival of voyagers on New Zealand and Easter Island in the last 1000 years.
Population dispersal to new continents began in … 60–24 ka … when continental shelves were exposed, ice sheets had advanced in the northern hemisphere and global temperature was lower. These were not full glacial conditions but a complex of warmer and colder phases. The lack of extreme conditions, either full glacial or interglacial, makes it difficult to identify a simple environmental cause (Jacobs et al. 2008).
Neural changes have been put forward to account for the changes in the 40 ka human revolution and in particular the mutation for the FOXP2 ‘language’ gene. However, analysis of the Neanderthal genome has revealed the human form of the gene, suggesting that it dates back at least to the last common ancestor of Homo neanderthalensis and Homo sapiens, estimated at some 500–700 ka, while anatomical evidence of a Neanderthal hyoid from Kebara Cave confirms their capacity for speech production.
One solution to the different ages between South, East and North Africa, the Middle East and Europe and Australia for the appearance of the commonly cited proxies of modern behaviour (e.g. use of shellfish, shell beads, ochre and microliths) have stressed the importance of demography. By estimating ancestral population size, and assuming demography determines the maintenance of cultural complexity … the different timings of the human revolution are explained by the moment that the size of any one regional population passed a critical threshold. How, or why, this threshold was repeatedly broken among Homo sapiens is unclear. However, genetic diversity in Neanderthal mtDNA from a wide geographic sample suggests that their effective population size was much smaller than that eventually achieved by Homo sapiens.
Materials
During the third movement there was experimentation with a range of new materials and social forms. Three materials, from a long list, serve here as an example of these innovations, shellfish, ochre and ivory, while new social forms include the elaboration of surfaces, beads and composite tools.
Shellfish were exploited at Pinnacle Point 160 ka ago. The significance is twofold. First, utilizing these highly productive resources is associated with greater harvesting and processing costs and therefore indicates an intensification and broadening of dietary breadth. Second, they are a pointer to the use of ecologically rich coastal areas that could promote and sustain larger local populations… Moreover, stable-isotope data from the second movement reveals significant use of freshwater aquatic foods among Homo sapiens populations, but not Neanderthals, in Europe.
Shell was widely used for decorative ornaments, as well as tools in island Southeast Asia, and includes ostrich eggshell as well as species of small marine mollusca. The former are chipped and ground while the latter are pierced for suspension, as at Skhul Cave 130 ka. Perforated Nassarius shell beads are found in South and North Africa by 80 ka.
Ivory beads are also common towards the end of movement 3 in the Upper Palaeolithic of Europe as at the Vallon de Castelmerle … Furthermore, they are often associated with burials and interpreted as evidence for headgear and clothing, as at Dolní Věstonice. Ivory was fashioned into items as varied as spears and flutes. These social forms were produced by a variety of techniques including soaking, steaming, cutting, gouging, drilling and polishing.
Ochre use appears at Kapthurin 280 ka and is present at … Pinnacle Point, 160 ka ago, at Sai Island and well established at Blombos Cave in deposits dated to 80 ka. The evidence includes many hundreds of pieces some of which show net-like engravings. Ochre can serve a variety of purposes. However, one use is clear and that was the alteration and elaboration of surfaces. These included clothing, bodies and rock walls as recorded in burials and the earliest cave art. This interest in adding and changing the surfaces of both containers and instruments is found with materials other than stone: bones and ivory were incised, engraved and carved.
Of particular interest is the evidence for composite artefacts and hafting. While examples … have been mentioned from the second movement, hafting technologies are found more widely in African sites by c. 285 ka … hafting has important conceptual implications as evidenced by understanding the properties of materials and how they can be combined. Hafting is a creative act and Barham points out that it involves comparable forms of recursive analogical reasoning that underpins complex language … The technical processes that involved combining materials in novel ways provides a set of proxies for early language capacity that matches the predictions from encephalization and community size. …
Microliths … are by definition small stone fragments hafted to form a variety of composite tools … [The] earliest pieces come from Twin Rivers (225 ka) and Pinnacle Point (160 ka). The large crescent forms associated with the later Howieson’s Poort and the move after 40 ka to highly standardized, smaller geometrics once again point to a gradient in technological change throughout the third movement. Size and weight reduction undoubtedly had adaptive advantages in the development of more efficient hunting technologies. But equally, the greater numbers now being produced of these highly standardized artefacts show how important they were as materials that linked hominins through ever-wider webs of contact and at differentiated scales of interaction.
Unsurprisingly, therefore, raw material movement expands considerably during the third movement. This applies in particular to Homo sapiens and the larger sets of materials and artefacts after 60 ka. Movements of shells, amber and stone regularly exceed 100 km, with some materials found over 1000 km from source. … Geometric microliths during the third movement focus 60–40 ka are frequently moved over long distances, especially in the case of obsidian in East Africa… [In] Europe … distances above 100 km are exceptional before the European Upper Palaeolithic at 40 ka. …
Emotions
Explaining innovation in the appreciation and use of materials, and their translation into social forms such as composite artefacts, music, art and religion has been the major preoccupation of palaeoanthropologists. Cognitive changes have been inferred from the appearance of this cultural complexity; a complexity that is also seen as a marker that society had changed fundamentally. The SBH adds to this model in important ways. In the first place, the prediction for community sizes of 150 applies to all equally large-brained hominins in the third movement.
As we have discussed above, community size is a proxy for social complexity which we define as the cognitive challenge presented by the integration of smaller units into these larger wholes. It appears then that there was more than one evolutionary pathway to meet these challenges. The archaeological evidence shows that large-brained Neanderthals, anatomically modern humans and modern humans (however awkward these terms may be) exhibited different strategies in different places at different times. …
Secondly, a focus on interaction and cognition in the social-brain model brings the emotions into play as a key resource in forming the bonds that bind (Fig. 1). While emotions have only weak or no material proxies for archaeologists to study, their affect is relevant to the distinction we have made above between social and technological competencies. Together with the properties, or affordances of materials, emotions underpin this co-evolutionary relationship that is then subject to selection. There had to be a capacity to amplify both the use of materials and the range of emotions for cognitive change to proceed and community size to increase. The evolution of language provides an example of one such capacity and the various stages by which it is believed to have developed can be understood by a model that puts the question: what drove encephalization?
We have made the case for movements 1 and 2 that the amplification of emotions and materials proceeded at different paces. In movement 1 the pace was set by the hominins’ engagement with materials, while in movement 2 emotions were further amplified in the context of an advanced theory of mind. The third movement saw both developmental pathways.
Before 50 ka, the small spatial scale, as revealed by raw-material transfers, and the modest innovations in technology among hominins in Africa, Europe and Asia, of which hafting may be the most significant, have to be set alongside continuing encephalization throughout the movement. While effective population sizes may well have been small, these estimates ignore the organization of anatomically modern humans and Neanderthals into larger social communities. Irrespective of the size of their meta- populations they would still have had to deal with issues of cognitive load and the demands of social interaction, stemming from increased numbers of social partners and sub-units in the community rather than the population.
Several solutions can be proposed.
Keeping the time and distance between social interactions to a minimum allowed by the pressures of fission and fusion would preserve the emotional force that arises in situations of co-presence. The psychotropic responses to social laughter, singing and crying demonstrate that force. Furthermore, innovations in social forms would be selected that boosted the impact of meetings and gatherings. Examples would include communal hunting, mortuary rituals, colouring the surfaces of the body and the structured use of hearths for conversation, eating and socializing. None of these are exclusive to the third movement, but all of them, as the archaeological evidence reviewed here shows, were amplified.
Selection for more complex language, that formalized those second-order emotions and expressed a theory of mind through other means than by material metaphors, would be favoured. The cognitive demands of encephalization were therefore met by emotional amplification to expand social competencies within the community.
The alternative, and the solution increasingly adopted during the third movement by Homo sapiens, was to explore the variety of technological competencies. This was achieved through a wider engagement with the possibilities for amplification afforded by materials in combination with emotions, and we have touched on several of these innovations. The larger community was no longer the problem for hominin social cognition. Rather, by turning the problem outwards, under the selection pressure to expand population range, social interaction over distance and time became the test. The requirement was to extend relationships while at the same time preserving the emotional basis on which they were based. In other words, to project what could be achieved by face-to-face contact into a wider social world of separation and infrequent contact.
The social form that met this challenge was a relationally-based system of social organization, typified by kinship. The unintended consequences of such a relational system led to a global distribution for Homo sapiens but this could not have been achieved without the amplifying effect of materials. Among these technological competencies was the importance attached, towards the end of the third movement, of intensely fragmenting stone to produce microliths and the transfer of raw materials over greater distances. The conceptual change … that led to relationally-based organization based on inclusive categories is matched by the shift after 60 ka towards artefact forms of container design: boats, baskets, clothes and houses. These artefacts now contained bodies, materials, people and their relationships in ways that served as analogues for innovations in kinship based social organization. Social and technological competencies co-evolved to facilitate not only the larger community sizes but also population growth and dispersal seen so dramatically in the peopling of Australia, the near-Pacific and the Americas.
Conclusion: towards an aesthetics of the Palaeolithic
… To illustrate the co-evolutionary relationship between the central elements … we have discussed new social forms as varied as social laughter, music, composite-hafting and the control of fire. Archaeological evidence is abundant for the complexification of social forms through activities such as fragmenting, accumulating, containing and wrapping that change during the three movements of the Palaeolithic. As a result we have been able to reexamine the disconnect in the second movement where the implications for social complexity of large-brained hominins is apparently not met by a surge in new conceptual traits and technology. We conclude that the three movements are different archaeologically because of the varied emphasis placed on materials or emotions to solve the adaptive problems of ever larger brains. …
Tell your friends and colleagues about Social Science Files
Social Science Files displays multidisciplinary writings on a great variety of topics relating to evolutions of social order from the earliest humans to the present day and future machine age.