Whallon's population model

Whallon R. 1989. Elements of cultural change in the later Paleolithic. In: Mellars P, Stringer CB, editors, The human revolution: Behavioural and biological perspectives on the origins of modern humans. Edinburgh: Edinburgh University Press. p 433-454.

I was really privileged to have Bob Whallon's course when I was at Michigan. It certainly taught me almost everything I know about population structure in foraging populations, and if not for that knowledge, I would probably not have returned to consider genetic variation from the perspective of population structure. Now I am pursuing topics much closer to Whallon's own interests, in the relation of information theory to group structure in ancient humans. This article, from the Human Revolution volume, is the best statement of Whallon's thinking on these issues.

He introduces the paper with one of the central issues of prehistory: why do so many things appear to happen essentially simultaneously and independently in different regions of the world during the Upper Paleolithic? The case in point is the migration of people to Australia and the New World, and Whallon's explanation is organizational and cognitive (433):

These explanations postulate not only the emergence of new socio-cultural structures as others also have proposed (Gamble 1983), but that these structures, in turn, would have required the development at this time of even more fundamental human capacities for conceptualization and communication.

Whallon builds his argument from a number of assumptions, and these are worth enumerating:

  1. Human population densities are ultimately resource-limited. Beyond some minimum population density, human populations cannot maintain themselves in a geographic region, because of the impossibility of maintaining breeding relations. This point relies heavily upon the early work of Martin Wobst, who attempted to determine the minimum sizes possible for foraging groups under the condition that mates must be available for maturing individuals (Another review available here).
  2. "[S]cales of of geographical movement and contact among hunter-gatherer groups" are themselves conditioned upon the kinds of foraging strategies that are within the cognitive range of a human group. Some environments fluctuate wildly, and may necessitate more in the level of movement and alternation of resource base than would have been possible for humans at a given adaptive level.
  3. Conditions (1) and (2) together imply that some large territories will be simply uninhabitable, because of the constraints on human populations in ecological adaptability and the numbers necessary to maintain occupation.
  4. Some constraints may be overcome by the application of suitable communication and movement strategies. If appropriate strategies became available, they would allow the exploitation of formerly uninhabitable regions.
  5. Low-density populations face informational limits. When extensive movement and a wide geographic range for groups is necessary, it becomes less possible for individuals to have "direct knowledge and immediate, face-to-face contact" with other individuals and groups, including potential mates, trading partners, and competitors.
  6. An essential feature of modern human language is "displacement." This skill is necessary to refer to objects and relationships not immediately present, and thereby forms a substitute to the direct, face-to-face communication that would otherwise be the only way to convey such concepts.
  7. Another essential element of human social life is the ability to synchronize social expectations among groups, at least to a degree necessary to readily facilitate the movement and establishment of individuals into new groups. Whallon contrasts the human situation with the frequently troubled and violent integration of dispersing primates into new groups. In his view, humans have alliance networks to facilitate such social integration, which are themselves dependent on the displacement function of language for the communication of expectations and abstract categories accompanying such human relations. Whallon observes that kinship categores are among this class of abstract relations that exist in all human groups.
  8. Decision-making ability is maximized in human groups when the number of decision-makers is around six (Johnson 1978; Reynolds 1984). Beyond this size there is strong pressure for hierarchicalization of decision-making. </p> </ol>

    Whallon sees several aspects of human societies as outgrowths of this change in communication ability. These include kinship, collective foraging strategies, division of labor, ability to plan for the future, and oral history. This last may be the most important, because Whallon sees it as an adaptation to adjust to temporal fluctuations in resource access. In brief, if people can remember the last time something bad happened (such as a drought) and can remember what they did to adjust, they can communicate that information to their children or grandchildren for use next time similar events happen.

    Moving from a situation in which knowledge of the past is restricted to individual memories to the sharing of such memories through an ability to refer to them and talk about them creates something new: a group memory. Group memory provides entirely new opportunities, and results in the devleopment of a number of cultural mechanisms for information storage, retrieval, and use, whose roles within cultural systems are complex but highly important (cf. Mine 1986). Without going into the details of these, we only will consider briefly here the fact that the fundamental effect of any and all of these mechanisms, beginning with simple verbally-shared individual memories, the basic and possibly earliest form of group memory, is that they increase the time depth of information available to the members of any group significantly beyond the life-span of an individual.
    The most obvious effect of this expansion of the time depth of information available to a hunter-gatherer group is that it allows adaptation to environmental fluctuations with a periodicity greater than the average individual life span (444).

    Whallon gives an estimate of this time span, figuring it to be roughly equal to three to five generations, or 60 to 125 years. He places oral history, myth, and other means of recalling information over long times as elements of this information storage system.

    He also puts together two opposing ideas from the information standpoint that may constrain the size of hunter-gatherer groups.

    It is perhaps in this light that the universally observed number of some 25-30 members (6 nuclear families) in recent hunter-gatherer minimal bands may be seen to have an organizational basis. Both the increasing quality of decisions with the involvement of more decision-makers (Johnson 1978) and the exponentially decreasing risk of group extinction (Wobst 1974: 171-172) would confer advantages to larger groups up to the level of six family units, beyond which it becomes increasingly difficult to maintain both effective decision-making and an egalitarian organization.

    Egalitarian organization is a fundamental aspect of hunter-gather organization that is probably impossible to change, considering the lack of resource hoarding or other means of maintaining power inequities. Larger groups would almost certainly fission if they could do so, rather than allow voluntary resource inequities to perpetuate themselves. Thus, the optimum number of decision-makers might be assumed to be a mental adaptation to the kinds of groups that were typical for extrinsic reasons. Under this assumption, the system would continue indefinitely because of the reinforcement from both mental and ecological realities.

    One of the most interesting emerging ideas here I would call the "information economy." Whallon's model implicitly postulates two stages, with a threshold between them. In the earlier stage information is highly valuable, but it can be obtained only through direct perception or "immediate, face-to-face communication." Whallon allows that this earlier stage may include symbolic communication, particularly of the sort encompassed by Bickerton's (1990) concept of a protolanguage.

    It is in the later stage that information can itself function as a commodity.

    Thus, it would seem that two of the important blocks to human expansion at any given level of technology into environments of low resource density and predictability are defined by communicational and social abilities: the ability to know about mates and resources within the physically attainable region, and the ability to assure access to these once known....On the other hand, the development of the communicational abilities necessary for: (1) the adequate transfer of information, and (2) the creation of the social networks necessary for such information flow, as well as for assurance of access to mates and resources over an adequately large area and sufficient number of local groups, both seem to repose on the emergence of a roughly equivalent level of language competence (440).

    If information can be transmuted between these two symbolic categories--knowing about things and assuring access to things--then information itself may bear a value extrinsic to its own initial generation. This economy is based on a currency whose value is constantly uncertain, since the intrinsic value of any single piece of information may be unknown to sender, recipient, or both. This dynamic establishes a dynamic in which cooperation is much more beneficial than defection, since the value of any single piece of information may be unknown to one who holds it. Only by pooling information maximally will the possible benefits of information be maximized.

    On the other hand, a very intelligent agent may be able to judge the value of information more accurately. And it may become possible to withhold information strategically, exchanging it only for other information (remember that this includes assurances of resource access) of great value. And one might be able to manipulate the symbolic system to generate spurious information that is nonetheless believed to have great value. The attribution of malevolent events to "witches," the propitiation of certain gods, and other concepts of natural forces no doubt fall within this category of information phenomena. Playing the information economy in this way would lead to a selection pressure for manipulation of the symbolic space, as well as for accurate detection of such manipulation or cheating.

    Potential problems

    There are a few weak points in Whallon's scenario. For example (436):

    Inability to obtain adequate information, either in terms of reliability and accuracy or of the area covered, on the existence and location of needed mating partners or subsistence resources, subjects individuals and groups to risks of failure to reproduce at a sufficient rate or of nutritional stress and eventually starvation. As outlined above, such risks and the penalties for failure grow with decreasing resource density and predictability.

    This is intuitively appealing, but ultimately relies on a fallacy about population density. Sure, low-density human populations were faced with resource stress. But high-density populations were almost certainly under just as much resource stress. Compared to other hominoids, humans have a high intrinsic rate of population increase, and we can expect that they were near the maximum possible population density in most of their range. This means that the competition for resources was greater in higher-density regions, not less. And it almost certainly means that whether peripheral populations in marginal regions lived or died had little relevance to the largest proportion of ancient humans. It may be true that habitation of low-resource-density regions required advances in communication and cognition. But when humans lived in both low-density and high-density regions, they probably faced equal or greater resource stress in high-density regions.

    It is natural to focus on the expanding populations in low-density environments, because these new populations are one of the major gross differences in the archaeological record of the latest Pleistocene when compared with earlier time periods. But the most important changes likely occurred in the heart of the long-occupied human range. These changes are more or less invisible, since the important ones involved not artifact types but instead organizational principles. However, we can infer that they happened based on Whallon's argument or another like it.

    Another issue is the degree to which hunter-gatherer populations track their environments.

    One result of these shifts, universally observable today among hunter-gatherers and the source of frequent comment and speculation, is that human population densities would appear more and more of the time to be below the supposed 'carrying capacity' of their environment. The resource 'lows' to which the existence of a shared, group memory allows a population to adapt would be less frequent, with the consequence that periods of resource stress due to fluctuations that reach or exceed a group's abilities to respond effectively would occur at wider intervals. The phenomenon of adaptive responses being tuned to longer-term, larger resource fluctuations, so that field studies and observation (including ethnographic expeditions) normally find populations under non-stressed conditions in which many important adaptive responses are latent and cannot be seen in operation, is well known also in the ecological study of many species (445).

    This passage appears to be making two distinct arguments. The first is that human populations are adapted to long-term resource fluctuations, so that they typically maintain themselves at lower densities than can usually be maintained. Their "adaptations" prepare them for future resource stress, in other words, by limiting their population growth. This argument is simply nonsense from an evolutionary perspective; there is no advantage to anyone's genes in limiting their reproduction in anticipation of population stress far in the future.

    The second argument is more subtle. If humans have successfully adapted to low-resource times by pooling information from previous times with similar ecological stress, then they may be able to maintain a larger population during such times and recover more quickly from them. To the extent that humans are self-limited in resource availability, these information adaptations will tend to smooth resource access over time, minimizing fluctuations (at least with respect to their effect on human resources, if not on the absolute productivity of ecosystems or similar measures). This would not cause humans to be below the carrying capacity, however; it would cause humans to more nearly match the carrying capacity over more of the time.

    I think the "well below carrying capacity" assumption is basically false. The human population has likely been at or close to its carrying capacity until very recent technological changes. Every evidence from history suggests that human populations grow quickly in the presence of enough resources, and such growth rates expressed across tens of thousands of years could not help but fill areas to their maximum population density. The idea that there is a pool of unused resources depends on false logic about what might be accomplished by a larger population, ignoring the consequences of higher exploitation over longer time periods (and thus the feedback between human populations and their environments) as well as the energetic costs of more intensive foraging. If humans expend 3000 calories or more a day to forage as effective hunter-gatherers, there will be diminishing returns to longer and more intensive foraging, in energetic, cultural and social terms.

    The idea that six decision-makers optimizes decision effectiveness is taken from empirical research. But many questions are left unanswered concerning this value. If larger groups were adaptive (because they had significantly longer half-lifes, for example) then why couldn't humans adapt to be better decision makers with eight or ten individuals, instead of six? Is there a fundamental organizational contraint related to time, or argumentation? Or is this a purely mental limit of humans, and some computer might work well with a hundred decision makers or more? Is physical force sitting at the root of this, with some minimum number being necessary to avoid the possibilty of lethal coalitions?

    References:

    Johnson, G. A. 1978. Information sources and the development of decision-making organizations. In C. L. Redman et al. (eds) Social Archeology: Beyond Subsistence and Dating. New York: Academic Press: 87-112.

    Mine, L. 1986. Scarcity and survival: the role of oral tradition in mediating subsistence crises. Journal of Anthropological Archaeology 5: 39-113.

    Reynolds, R. G. 1984. A computational model of hierarchical decision systems. Journal of Anthropological Archaeology 3: 159-189.