The term hunter-gatherer refers to an adaptation in which people subsist almost entirely on plants and prey they take in the wild. Except for some less self-reliant groups in the late twentieth century, hunter-gatherers produce nearly all the food they consume with gear of their own making, acquiring relatively little by means of trade. Therefore, the size, distribution, and density of hunter-gatherer populations are conditioned by the environments those peoples inhabit and the knowledge and technologies at their command and have varied dramatically over time in response to changes in both factors.
From the Pleistocene to the Holocene
The boundary between the Pleistocene (Ice Age) and Holocene (modern) epochs, about 11,600 b.p. (i.e., years before the present time), marks a major divide in this variability. The populations of archaic human hunter-gatherers of the Pleistocene (notably Homo habilis, H. erectus, and H. neanderthalensis) were presumably low as a consequence of their limited skills and intellectual abilities. Hunter-gatherer populations may have grown larger and denser after the emergence of anatomically modern humans in Africa (about 150,000 b.p.) and certainly did so after the appearance of the essentially modern behavior repertoire that signals the Upper Paleolithic (about 40,000 b.p.). However, despite essentially equal technological and intellectual abilities, Upper Paleolithic hunter-gatherer populations of the late Pleistocene never grew as large or dense as their Holocene counterparts. This was due to climate.
In comparison to the comparatively quiescent Holocene, Pleistocene climate changed frequently and abruptly, often going from nearly glacial to nearly interglacial conditions within a decade or two. Compounding this situation, atmospheric concentrations of carbon dioxide, which is essential to plant growth, were so low during the last 50,000 years of the Pleistocene that overall plant productivity and seed yields were only two-thirds of those in the Holocene. This combination of chaotic climatic change and low environmental productivity severely limited the opportunities of Pleistocene hunter-gatherers to develop stable, intensive adaptations capable of supporting large populations. As documented in the Middle East (Natufian culture) and Japan (Jomon culture), when rising carbon dioxide levels increased environmental productivity near the end of Pleistocene, a few hunter-gatherer groups developed more intensive and plant-dependent adaptations that supported larger and more sedentary populations. Rapid climate change, however, continued to limit these tendencies until the Holocene.
Responses to Climatic Change
Some hunter-gatherers responded almost instantly and in revolutionary ways to the onset of the stable, productive Holocene climatic regime. Jomon (Japan) hunter-gatherers intensified the use of plants, shellfish, and fish to support large, permanent settlements in a heavily populated landscape. Some hunter-gatherers in the Middle East, in contrast, shifted to part-time agriculture and began to compete for resources and space with the remaining hunter-gatherers, who were forced either to retreat and displace other hunter-gatherers or to work harder to glean more costly resources from shrunken territories.
Though its timing varies, this pattern of hunter-gatherer intensification eventually was repeated everywhere during the Holocene. The behavioral details differ depending on local resources, but the trend is always toward maximizing the rate at which these resources are acquired per unit of space, producing more nucleated, sedentary, and densely settled populations. This form of maximizing is a response to competition. Without competition, hunter-gatherers usually maximize the rate at which resources are acquired per unit of time by minimizing the amount of time expended in their acquisition.
Time-minimizing hunter-gatherers are highly mobile, quickly leaving locations where resources have begun to diminish in search of others where returns are higher. Population growth increases the chances that another group has depleted these other prospective locations. This reduces the potential rewards of moving and increases the tendency to stay put and maximize the total amount of resources acquired from a smaller area by adding more costly roots, seeds, and small prey to the diet. In this way, the larger trajectory of hunter-gatherer intensification in the Holocene (including incipient agriculture) may be interpreted as a response to global population growth made possible by global climate change. The hunter-gatherers observed by anthropologists are representative of only the end of this trajectory, not of hunter-gatherers in general.
To illustrate this point, the population densities and maximum social group sizes of ethnographic hunter-gatherers are an order of magnitude larger, and their median and minimum territory sizes an order of magnitude smaller, than is likely for any time in the Pleistocene or early Holocene (Table 1). Ethnographic fertility and mortality more closely approximate values that seem reasonable for the late Pleistocene–early Holocene, although Pleistocene infant mortality probably was higher and total fertility probably was lower. In any case, the rapid population growth of some Eurasian hunter-gatherers almost immediately after the onset of the Holocene suggests that Pleistocene hunter-gatherers were capable of the same thing when rebounding from environmental disasters, growing rapidly at annual rates that may have ranged between 1 percent and 3 percent during short periods of optimal climate.
The Timing of Population Changes
The timing of hunter-gatherer intensification varies greatly within the Holocene. In contrast to their counterparts in Eurasia, where intensification occurred relatively early, hunter-gatherer populations in southern Africa, Australia, and much of North and South America remained relatively low well into the Holocene, rising rapidly to historically observed numbers only 3,000 or 4,000 years ago. Technology and environment seem lesser obstacles to these transformations than is the development of social
conventions enabling the holding of land and hoarding of resources, without which individuals are insufficiently rewarded for the extra labor they must invest to intensify resource production. The many cases of late Holocene intensification make it clear that hunter-gatherer populations are probably always close to the limits imposed by environment, technology, and behavior but that the force of population growth is not a major source of innovations that breach those limits. (If it were, intensification would occur uniformly early.)
Simulations by Gary Belovsky (1988) and Bruce Winterhalder and colleagues (1988) show how hunter-gatherers and their resources are linked in a dynamic feedback cycle that makes population growth self-correcting. When resources are abundant, hunter-gatherer populations rise until resources are depleted, which causes the population to fall. As the population continues to fall, resources rebound, starting the cycle again. The whole cycle takes something like 90 years. Thus, hunter-gatherer populations are resource-limited but not static, and groups under the same limits may vary substantially in size, depending on which stage of this cycle they are in. These simulations also suggest that because intensive harvesting prevents resources from rebounding, hunter-gatherers who limit their foraging efforts will often maintain higher population densities than will hunter-gatherers who do not.
Belovsky, Gary E. 1988. "An Optimal Foraging-Based Model of Hunter-Gatherer Population Dynamics." Journal of Anthropological Archaeology 7: 329–372.
Bettinger, Robert L. 2001. "Holocene Hunter-Gatherers." In Archaeology at the Millenium, ed.G. Feinman and T. D. Price. New York: Kluwer/Plenum.
Binford, Lewis R. 2001. Constructing Frames of Reference: An Analytical Method for Archaeological Theory Building Using Ethnographic and Environmental Data Sets. Berkeley: University of California Press.
Keeley, Lawrence H. 1988 "Hunter-Gatherer Economic Complexity and 'Population Pressure': A Cross-Cultural Analysis." Journal of Anthropological Anthropology 7: 373–411.
Kelly, Robert L. 1995 The Foraging Spectrum: Diversity in Hunter-Gatherer Lifeways. Washington, D.C.: Smithsonian Institution Press.
Winterhalder, Bruce, W. Baillargeon, F. Cappelletto, R. Daniel, and C. Prescott. 1988. "The Population Ecology of Hunter-Gatherers and Their Prey." Journal of Anthropological Archaeology 7: 289–328.
Robert L. Bettinger