FORAGING SYSTEMS & "ORIGINAL AFFLUENCE"
Eric A. Smith, Dept. of Anthropology, University of Washington
http://courses.washington.edu/anth457/foraging.htm

[Note: Read "Intro" plus "Original Alluent Society?" sections for Oct. 21st class; read section on "Foraging Strategies" for Oct. 23rd.]
Intro
A significant amount of research in ecological anthropology is devoted to studies of hunter-gatherer (H-G) populations, also known as foragers; this is out of all proportion to the number & size of such populations [see bottom panel of "Man the Hunter" map]
This preoccupation with such a rare mode of subsistence has 2 explanations:
1) Up until about 10,000 yrs ago, when crops & herd animals first domesticated, all humans lived as foragers; depending on when you mark boundary between humans & pre-humans, we have been foragers for 75% to 99% of our history [see map, top panel]
2) Beginning with Steward in 1930's, H-Gs have been viewed as more closely adapted to local environment, hence more subject to ecological analysis, than other kinds of human populations (though of course there are dissenters from this view...)
Despite this continuous interest in foragers, anthropological & ecological views of them have undergone marked shifts (see Kelly 1995: ch 1 reading)
Until about 30 yrs ago, H-Gs were seen as culturally impoverished, ecologically vulnerable
This stereotype stemmed from Victorian notions of cultural progress (from "savagery" to "barbarism" to "civilization"), which viewed contemporary foragers as survivals from earliest stage, living lives that were "nasty, brutish, and short" and too hard-pressed by the constant struggle to stay alive to develop culture beyond the most rudimentary forms
 
THE ORIGINAL AFFLUENT SOCIETY?
A few studies in 1960s (Richard Lee w/ !Kung San, various researchers w/ Australian Aborigines) gathered detailed quantitative data on contemporary H-Gs, leading to rather sudden abandonment of old view and adoption of new orthodoxy in H-G studies, a trend that crystallized with the Man the Hunter conference & book (Lee & Devore 1968)
The new view established by these studies includes several tenets:
1) H-G have as much or more leisure time than agriculturalists
2) Food supply is abundant, and population regulated below Cc
3) Composition of residential groups (camps, local bands) is flexible, and land ownership is absent (no "territoriality")
4) Bulk of food supply comes from gathering plants (primarily women's work)
The anthropologist Marshall Sahlins went so far as to label H-Gs the "original affluent society", with a "zen economy" where scarcity has been banished not by boosting production, but by reducing economic wants to a minimum (Sahlins 1972, as discussed in Kelly 1995 and Winterhalder 1993 readings)
This new view of H-G has become the orthodoxy in anthropology, effectively inverting the previous "nasty, short & brutish" stereotype
However, the empirical basis for the new orthodoxy was rather slim (a handful of studies with actual data, and even those based on just a few weeks of data collection), and there are some weaknesses in its theoretical basis as well, raising doubts that it provides an accurate portrayal of H-Gs at all times and places
Let's consider the four tenets of this new orthodoxy (listed above), and examine the logic & evidence behind each of them
 Work Effort
The old stereotype that foragers work incessantly to meet bare minimum of food needs, and that work effort is thus simply a function of getting enough to survive, has been laid to rest by empirical evidence from several populations
This evidence shows that foragers often work shorter hours than the average ethnographer, averaging some 6.5 hours per day  (see Hames 1992 time allocation graph)
However, there are some problems with concluding that foragers live a life of relative leisure
1. How do we define work?
In time allocation studies, work is typically defined as activities that secure livelihood conducted outside of home
This overlooks activities that are necessary for subsistence which take place within the home or camp (food processing, tool mfg. & maintenance)
One study showed that including such tasks can as much as double total "work" time (Hawkes & O'Connell 1985, on mongongo nut processing among !Kung San)
Focus on direct subsistence tasks (especially food production) also leaves out other activities essential to survival and reproduction, such as childcare or maintenance of social relations
In sum, there is no clear agreement on how to define "work" in a general, non-ethnocentric manner; the best we can do is to specify what activities are included in our tabulation, & why
2. Is there a clear trend?
Can we conclude from the available time allocation data that foragers generally work less than people in other modes of subsistence?
There are two reasons to doubt this (if by "other" modes, we mean "all other")
First, available cross-cultural evidence indicates that swidden horticulturalists (from Amazonia and from New Guinea highlands) work less than H-Gs (see Hames graph again)
On other hand, intensive agriculturalists (pre-industrial or industrial) work much more than either H-Gs or swiddeners, while average work time declines somewhat in advanced industrial society (ditto)
Second, there is problem of sample size: quantitative data on time allocation only available for a handful of forager societies (n=4 in Hames' compilation, though this has doubled in the last dozen years), and no data at all for sedentary foragers with complex socioeconomic systems (e.g., Native California, Northwest Coast, prehistoric Woodland culture in E. No. America, upper Paleolithic Europe, northern Japan)
For the 4 H-G groups in Hames' sample, daily mean work effort ranges from 5 to 9 hrs, a range which overlaps with several groups in other subsistence modes
Even passing acquaintance with statistics would caution us about drawing any firm conclusions on time allocation trends from these data
 Resource Supply and Demand
Second major tenet of "new orthodoxy" is that H-Gs regulate their population densities below the "carrying capacity" of environment in order to avoid overexploiting their resources and degrading their environment
Besides the theoretical problems with this argument (some of which have been discussed in previous lecture notes), it is empirically problematic for two reasons:
First, evidence indicates that many foragers are nowhere near overharvesting resources (for example, among the !Kung, Lee [1979] notes that millions of mongongo nuts -- the !Kung staple -- rot on the ground every year, and Hill [1983] has calculated that !Kung annually harvest <1% of large herbivore biomass in their area, whereas sustainable yield = 10-20%, depending on the species)
Second, Nancy Howell's detailed demographic study (Howell 1979) suggests that the low birth rate of !Kung nevertheless results in an annual population growth rate of ~0.5%, which although low is still positive (and as we know from population ecology, could not persist long without resulting in skyrocketing exponential population expansion); other detailed demographic studies of H-G populations lacking market involvement and external medical resources have also revealed positive growth trends (e.g., Blurton Jones et al. 1992 on Hadza; Hill & Hurtado 1996 on Ache)
Theory and evidence (e.g., Blurton Jones et al. 1994) suggests that main limits on forager population density may not be food abundance per se, but rather the tradeoffs between foraging effort and other factors (parental care, avoidance of mortality risks, etc.)
In other words, rather than simply look at how much food is out there in the environment of a given forager population (the "Cc" approach critiqued by Dewar 1984 reading), we need to pay attention to the costs of harvesting this food (in time, risk, etc.), and how the marginal benefits of foraging compare to those from alternative activities (see below for explanation of the concept of "marginal" benefits & costs)
In addition, in most environments the resource base likely fluctuates greatly from season to season and year to year (due to variation in climate, etc.)
If so, H-G equilibrium population size might be adjusted to leanest period over 1-2 generations, not to average abundance of resources
Hence, over short time-spans it will often appear that a larger population could be supported, but since humans have relatively long generations and cannot demographically track short-term fluctuations in abundance of resources, this idea of "underexploited resources" (Sahlins 1972) may be quite illusory
A more empirical critique notes that if H-Gs did indeed maintain their populations consistently below carrying capacity (as determined by food availability), they would have little need to buffer fluctuations in resource abundance; but in fact all foragers employ one or more means of buffering such variation:
1) food storage; the rarity of such storage in many H-G groups has been used to support the "original affluence" view, but this overlooks the fact that storage entails significant labor costs (and sometimes social costs), and is only practical when resources are so dense that populations can be seasonally sedentary (e.g., NW coast), or maintain a systems of caches (e.g., some parts of Arctic)
2) exchange between groups; this has high transport costs, but is common for relatively rare items, and for a wide range of resources among more sedentary groups (e.g., Native California), especially where water transport is used (e.g., NW Coast)
3) moving people around to match shifting resource availability is widely used, and effective whenever resource fluctuations are spatially uncorrelated (due to game movements, patchy rainfall, etc.)
4) physiological storage (feasting on abundances, accumulating fat reserves) is universal
Existence of these buffering mechanisms implies that food is often scarce relative to demand, if not necessarily relative to survival (though famine among foragers is not unheard of, particularly in arctic/subarctic climes)
Here is what Kim Hill & Magdalena Hurtado (1996:319-20) say about "original affluence," on the basis of their detailed long-term observations of foraging ecology and reproductive ecology in two H-G societies (the Ache of Paraguay, and the Hiwi of Venezuela):
...the concept of the "original affluent society" (Sahlins 1972) as a characterization of hunter-gatherers is flawed. The Ache eat better than almost any other group of foragers ever studied (Hill et al. 1984), and they weigh considerably more than well-known groups such as the !Kung, yet data clearly indicate that they do not get "enough food to meet their needs." More food is shown to impact positively on fertility of both sexes and may also increase child survival... Since individuals consistently voice a desire for high fertility, and high survivorship, and such a preference would be favored by natural selection under many conditions, there is no basis for the assertion that the Ache obtain all the food they need. Regardless of how many hours they work at acquiring food, neither the Ache nor members of any other foraging society can be shown to meet their food needs in any biological sense. Indeed, neither the Ache nor any other traditional people with whom we have worked in the past two decades agrees with the proposition that they obtain all the food they need. Instead, they emphatically insist that they are hungry and would prefer more food...
The "original affluent society" myth suggesting that our ancestors easily met their daily needs before we became greedy and began to desire more than that which is necessary is an idea that tells us more about late twentieth century anthropological thought than it does about the lives of foraging peoples. The "original affluent society" concept has no basis in empirical reality or biology, but it is also a cruel hoax because it leads members of modern societies to avoid the empathy or guilt that they should feel when considering the plight of people living under difficult conditions. Indeed, after seventeen years of working with foragers in three different countries and hearing the complaints of hunger, the cries of children, and having watched people suffering from less than desirable health, it is difficult for us to feel charitable towards those who have perpetuated this farcical myth in modern anthropology. Not surprisingly, the foragers with whom we have shared our lives feel the same way: "If he thinks that this is all the food we want, let him come down here and eat with us, and feed his children that which we feed ours" (Dawiya, a Hiwi forager, commenting in 1988 on our story about a man who claims that the Hiwi only work a few hours per day because they obtain plenty of food).
 Group Composition & Land Tenure
A third generalization that has been widely accepted since Man the Hunter is that H-Gs lack territorial boundaries and move freely over the landscape and between social groups
Although this generalization does not seem to be as problematic as the preceding two, the ethnographic evidence for it is nevertheless quite mixed
In general, while H-Gs do tend to be less sedentary than agricultural peoples, and to have less interest in property rights with respect to land, there is lots of diversity
Thus, in Native No. America alone, H-G land use patterns range all the way from very high mobility and near-total absence of land ownership among Shoshone of central Great Basin or Cree/Naskapi of eastern subarctic (in pre-fur-trade days), to kin group, family, or even individual ownership of resource sites among Northwest Coast and California Indians, with intermediate cases involving community ownership (and active defense) of territories in many cases (e.g., Alaskan Eskimo)
Later in this course (in section on "Land Tenure"), we'll examine extent to which such variations (including those found among agricultural and pastoral peoples) can be explained ecologically
 Gathering vs. Hunting
Fourth tenet of new orthodoxy is that gathering plant foods makes greater contribution to subsistence than does hunting of game
Given typical sexual division of labor, this would mean that women provide greater share of subsistence than men (an ironic conclusion for a conference & book entitled Man the Hunter!)
When the first quantitative studies of H-G diet (e.g., Lee on !Kung) appeared, they indicated that gathering provided 60-70% of food supply
This called into question the pervasive emphasis on (male) hunting in human evolution, standard analyses of H-G social organization, gender relations, etc.
Again, while this resonated with the contemporaneous social movements and social theory of the 1960s, we need to ask a basic question: are Lee's data for !Kung typical of H-Gs?
Answer is both yes and no, depending on how you define "typical"
If we consider all 181 societies classified as foragers in the cross-cultural compendium Ethnographic Atlas (EA for short), 23% have gathering listed as major source of subsistence, while 77% have hunting or fishing as major source
However, EA cases are unlikely to be representative of pre-agricultural period, simply because contemporary (ethnographically described) foragers -- the only kind tabulated in the EA -- are restricted to areas where agriculture & pastoralism is absent or marginal  [see graphs of EA cases by latitude & region]
Specifically, tropics and subtropics are poorly represented (57% of EA foragers are found N or S of 42° [latitude of NYC], vs. only 17% of non-foragers), and so are most continents (e.g., Native N. America contains 84% of EA foraging societies, vs. 25% of total EA societies regardless of subsistence mode [Hunn 1981])
If we control for latitude, we find a clear gradient: above 42° N, only 2% of cases have gathering dominant, while below 42° N, 51% do
Also not accurate to assume that gathering & hunting are allocated strictly along gender lines; many cases are known where men do substantial amount of gathering, and some cases where women fish & hunt, even large game (e.g., Agta in Philippines)
In sum, data suggest that H-Gs vary considerably regarding which sex or which type of food will dominate in subsistence, and that resource choice depends on what resources are available & most efficiently harvested in given locale (e.g., arctic & subarctic foragers would find it difficult or impossible to rely heavily on gathering -- edible plants are too scarce)
A more general point here is that explaining what causes variation in H-G subsistence cannot be accomplished w/ statistical averages or normative statements ("In general, H-G are....")
A much better research strategy is to develop and test explanatory theories of subsistence choice that might explain why some H-G rely mostly on plant foods, others on game, still others on fishing, etc.
Best available candidate for accomplishing this appears to be "optimal foraging theory," to which we now turn
 
FORAGING STRATEGIES
Optimal Foraging Theory
Optimal foraging theory (OFT) = branch of behavioral ecology concerned with explaining foraging strategies in all species of animals (bees, birds, and humans)
A thumbnail description of OFT = "decision rules for predators" (Krebs 1978)
Thus, although initially developed in evolutionary biology, OFT has many affinities to certain behavioral sciences (i.e., microeconomics & decision theory)
Some main characteristics of OFT:
1) Consists of models (simplified mathematical representations)
2) Assumes cognitive mechanisms controlling foraging behavior are "designed" by natural selection to respond to changing conditions in way that maximizes benefits to forager (thus, actor-based, flexible, not narrow genetic determinism)
3) Focus is on strategies (general decision categories, e.g., prey choice) rather than tactics (species-specific techniques of capture)
4) Models based on optimization approach:  decisions maximize some currency, given goals and constraints
OFT breaks complexity of foraging process into discrete decision categories:
1) Prey choice (a.k.a. diet breadth) = what to harvest 2) Patch choice = where to forage 3) Time allocation = how long to forage for each alternative 4) Social foraging = with whom to forage (group size) or share (food, information)
Will limit discussion here to prey choice (group size taken up later in course)
 Optimal Prey-Choice Model
The problem of what prey to harvest is addressed with prey-choice or "optimal diet" model
This model has been used by anthropologists and archaeologists wanting to explain prey choice and resource utilization patterns among H-Gs (reviews in Smith 1991; Kaplan & Hill 1992; Kelly 1995; Grayson & Cannon 1999; Winterhalder & Smith 2000)
Can use it to answer following kinds of questions:
1) Why are some groups specialized in their food resource choices, while others have more diverse diet?
2) Why does prey choice shift over short or long term? (some prey types taken at time 1 but passed up at time 2)
3) Why are abundant resources sometimes ignored?  Why are scarce resources sometimes taken whenever encountered?
4) How is optimal prey choice affected by changes in resource abundance? Forager population density? Technology?
Standard prey-choice model assumes following:
1) Prey (plants & animals) are divided into "prey types" (not necessarily Linnean species, but rather distinguished by return per unit handling time -- see points 2) & 4) below)
2) Foraging time consists of two mutually exclusive categories:  search time (for all acceptable prey types) and handling time (including pursuit once encountered, plus capture & processing; varies by prey type)
3) Prey items (not necessarily equal to individual organisms -- e.g., handful of berries, net-full of shrimp) are encountered singly and in uncorrelated fashion:  simultaneous search assumption
4) Forager can rank all prey types along single dimension of value per unit handling time (a.k.a. "post-encounter return rate")
5) Goal is to harvest set of prey types which will maximize the overall return rate (i.e., Total Harvest / Total Foraging Time, the latter consisting of search time + sum of handling times)
Given these assumptions, how would a forager determine the optimal range of prey types to harvest in any given situation?
Note that the optimal prey-choice model defines a central trade-off:
1) If specialize in highest-ranked (most efficiently harvested) prey type, face highest possible search costs per unit harvested (spend the most time passing up "unacceptable" prey types, waiting to encounter the top-ranked type)
2) If take all or most prey types, will have to harvest many low-ranked ones (i.e., ones with the lowest return per unit handling time)
Since both higher search time and handling time occur in the denominator of overall return rate (see 5) above), this tradeoff seems to create "damned if do, damned if don't" dilemma, but in fact defines optimal diet breadth as point where marginal decline in search cost = marginal increase in handling costs
Thus, model reveals a very simple decision rule for optimal solution: add prey types to the set taken, in descending rank order, until reach the jth prey type where Vj/Hj < SVi / (Ts + SHi)  [Note: V = value (e.g., calories) for each prey type; Ts = total search time; S = "sum of"; H = average handling time for prey items of each prey type]
Phrased in English, this rule says "Add prey types until the post-encounter return rate from a prey type is lower than the average rate of return for all higher-ranked prey types (including search time)"
The optimal diet thus occurs at the point that "adding" prey types to diet, in descending rank order (most efficient to least) leads to a decrease in the overall rate of return [see Kelly 1995:85-86 for an example]
Although optimal prey-choice model seems pretty formalized and abstract, the major elements actually correspond quite closely to concrete aspects of the foraging process, and its procedures are pretty straight-forward
Specific predictions/insights from the model:
1) What happens when high-ranked prey types become abundant? Search costs/unit harvest decline, hence optimal diet becomes more specialized (e.g., caribou hunters or salmon fishers during migration/run exhibit extreme specialization)
2) What happens when low-ranked potential prey types become abundant? Nothing should change if they lie outside the optimal diet (if mice are too costly to bother with, their increased abundance won't change this -- as long as must harvest mice one at a time)
These results contradict common-sense notion (found in much cultural ecology) that resources will be harvested in proportion to their abundance (e.g., that abundant food types will comprise bulk of the diet, etc.)
Prey-choice model predicts that as long as abundance of prey type does not alter its handling cost, a low-ranked type not worth taking when rare is still not worth taking when abundant; in fact, harvesting abundant low-ranked prey types can be very costly, as it will reduce time available for harvesting high-ranked prey types even more than if only harvest the occasional (because rare) low-ranked prey type
Thus, prey-choice model predicts that encounter rate with higher-ranked types determines if any lower-ranked type is in optimal set, and that encounter rate with a prey type has no effect on its own inclusion in this set
Important to note that optimal diet affected not by abundance of high-ranked prey types per se, but by encounter rate with each type; the latter can be determined by changes in forager density as readily as by changes in prey density; therefore:
3) What happens if foraging population increases (expanding population of h-g)? If all else remains the same, model predicts widening of diet (since now face a lowered per capita encounter rate).
4) What is effect of change in technology that lowers search costs (e.g., motorized transport)? Expect narrowing of diet breadth (due to increased encounter rate with high-ranked prey types)
5) Changes in technology that affect handling costs also significant: can change rank order of prey types, alter breadth of optimal diet, etc.
Quantitative tests of opt. diet model with h-g have been fairly successful, but too detailed to describe here (see Kelly, ch 3 reading, and click here for a graph of one empirical example, from the Ache Indians of Paraguay)
Good qualitative test of prey-choice model = Winterhalder (1981) on Boreal Forest Cree (Subarctic foragers in N. Ontario who became involved in fur trade in 1700s)
Before fur trade, Cree foraged on foot, with snowshoes, or by canoe; they used bow and arrow, rawhide snares, fishhooks, and spears to capture prey
Available information on diet breadth with aboriginal technology suggests an "intermediate" diet breadth
Involvement in fur trade led to adoption of more efficient "handling devices" -- wire snares, rifles, fishnets -- greatly reducing handling costs across wide spectrum of prey types (but not affecting search costs)
Thus, model predicts broad, generalized diet, and historical evidence bears this out
In contemporary period, handling technology little changed, but outboards and snowmobiles (not used for pursuit) have greatly reduced search costs
Resulting prediction is for narrowing of diet breadth, and contemporary Cree do specialize on a few high-return species (moose, hare, beaver, fish), passing up many species their ancestors harvested in fur-trade era
Considerable number of studies have found prey choice and other OFT models do quite well in predicting many features of resource decisions in H-G (and even, with suitable modification, among agriculturalists); the set of models are much richer than discussed here, and include considerations of patch choice, central-place foraging (e.g., forays from a village or camp), choices between producing (capturing own resources) or scrounging (hassling others for some of theirs), and so on
OFT has even been applied successfully to analyze search strategies in library databases and on the world wide web
Though models do not usually match data in every quantitative detail, to date no other explanatory framework does as well, and OFT seems to provide considerable insight into the logic of decision-making in foraging economies
 Summary
Main predictions from optimal diet model:
1) Prey types added to and dropped from diet in rank order of return/handling time
2) Abundance of high-ranked prey leads to specialization, while scarcity leads to broad diets
3) Inclusion of a prey type in optimal diet is independent of its abundance or encounter rate, and depends only on encounter rates with higher-ranked types
Note that these predictions are only reasonable where assumptions of model are met, especially those of 1) simultaneous search and 2) substitutability of prey (single currency such as calories)
If assumptions not met, there is no point in applying the model; however, there are alternatives for these cases:
1) patch-choice models
2) multiple-currency models (e.g., linear programming)
Furthermore, simultaneous search (random encounter) assumption not as stringent as might think, because this can be applied on a patch-by-patch basis (Smith 1991)
 References Cited
Blurton Jones, Nicholas G., et al. (1992) Demography of the Hadza, an increasing and high density population of savanna foragers. American Journal of Physical Anthropology 89:159-181.
Blurton Jones, Nicholas G., Kristen Hawkes, and Patricia Draper (1994) Differences between Hadza and !Kung children's work: Affluence or practical reason? In Key issues in hunter-gatherer research, ed. Ernest S. Burch, Jr. and Linda J. Ellanna, pp. 189-215. Oxford/Providence: Berg.
Dewar, Robert E. (1984) Environmental productivity, population regulation, and carrying capacity. American Anthropologist 86(3): 601-14.
Grayson, Donald K. and Michael D. Cannon (1999) Human paleoecology and foraging theory in the Great Basin. In Models for the millenium: Great Basin anthropology today, ed. Charlotte Beck, pp. 141-151. Salt Lake City: U of Utah Press.
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Winterhalder, Bruce and Eric A. Smith (2000) Analyzing adaptive strategies: human behavioral ecology at twenty-five. Evolutionary Anthropology 9(2):51-72.