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Chapter 4
THEORETICAL BACKGROUND
The functional relationship between human behavior and the environment is one of the foremost
areas of investigation in anthropological studies. Over the last two centuries, numerous anthropologists
have developed many theories to explain how the opportunities and constraints provided by a population’s
environment shape its demographics, behavior, and culture. My hypothesis is that changes in subsistence
patterns over time and space for the study area are the result of human foraging decisions based on need,
available resources, and technological capabilities. What follows is a brief overview of the theoretical
premises on which my hypothesis is based.
Cultural and Evolutionary Ecology Theories
One the most influential theories developed during the last century was Julian Steward’s 1955
theory of Cultural Ecology. The theory of Cultural Ecology can be defined as the study of how human
societies adapt to their environment, emphasizing how the arrangements of technology, economy, and
social organization (i.e., culture) within a society mediate the human experience of the natural world
around them. A key aspect in the formation and explanation of Cultural Ecology is the analysis of huntergatherer settlement and subsistence patterns.
The growing influence of neo-Darwinian biology and middle range (processual) theory in the
1960s and later caused many cultural ecologists to begin to incorporate testable concepts from evolutionary
ecology into their explanations. The individual, not the society, became recognized as the agent upon
whom natural selection acts (e.g., Winterhalder and Smith 1997). This assumption allows the adaptive
success of certain human behaviors to be tested in a systematic manner and is referred to as human
behavioral ecology. One of the more popular applications of behavioral ecology in anthropology has been
the examination of human foraging strategies.
In 1970, researchers C. Vita-Finzi and E.S. Higgs presented a model of hunting and gathering
economy known as site catchment analysis. Although their focus was on identifying the triggers associated
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with the transition from hunting and gathering to agriculture in the Middle East, the conclusions they drew
are general enough to be widely applicable to a number of resource economies and remain reflective of
processual theory. Vita-Finzi and Higgs based their theory on simple cost-benefit principles, supported by a
variety of ethnographic (e.g., !Kung Bushman) and historical (e.g., Chisholm 1968) examples.
A site catchment is defined as the area from which materials preserved in an archaeological
deposit are derived (Renfrew and Bahn 2005:172). Factors that determine a site catchment are available
resources, method of economy (mobile versus sedentary), population size, and site location. The interplay
of these factors led the authors to propose a daily maximum radius of 10 kilometers (6.2 miles) for hunting
and gathering populations and 5 kilometers (3.1 miles) for the more sedentary agricultural societies
(Renfrew and Bahn 2005:172-173; Vita-Finzi and Higgs 1970:5, 7). Distances farther than these consume
more energy than the resource to be acquired will provide, and are therefore considered uneconomical. The
model Vita-Finzi and Higgs devised provides a method for creating and testing hypotheses about
prehistoric optimal forging patterns on a localized, site based level.
Optimization models can be used to examine the strategic decisions involved in the acquisition of
dietary components. Optimal foraging theory uses a set of models to predict the behavior of animals while
they are foraging (Pyke 1984:523). Foraging success is measured by the costs and benefits of search and
pursuit. Costs include factors such as pursuit time, handling time, risk, and overall energy expenditure
(Bettinger 1991:87; Craw 2002:8; Pyke 1984:530). The benefits are that individuals who are able to
maximize their net rate of energy gain (measured as caloric intake) against their net rate of energy loss
should be fit enough to reproduce successfully and therefore be favored by natural selection (Kelly
1995:53).
Optimal foraging models have been successful in evaluating the dietary preferences among human
societies in both modern and archaeological contexts. Models that have been applied to anthropological
studies include patch choice, diet breadth, group size, and time allocation. Most of these models share the
idea that within the constraints of environment and culture, the goals and choices exhibited by human
foragers will be to ensure that maximum energetic returns will be obtained per unit of foraging time spent
(Smith 1983:640). As with biological models, return rates are measured by the energetic value found in the
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caloric content of the food items acquired. The operative assumption here is that the energetic net return of
prey item is approximately proportional to its body size or weight (Broughton 1994a:502-503; Broughton
et al. 2011:404, 423). This assumption allows resources to be ranked on a hierarchical scale according to
their post-encounter return rates. Predictive models can then be established based on the net energetic
returns provided by large and small-sized taxa.
The idea that certain resources are more highly ranked than others is a key element in the diet
breadth model. This model is also known as the prey-choice model and it provides a framework for
assessing how the relative costs and benefits of different resources (prey) are not only linked to their
energetic returns, but are also linked to their abundance in a given patch of land (Broughton 1994a:501).
For example, the higher caloric return and low handling cost of larger prey such as artiodactyls implies that
they will be a higher ranked dietary item on an encounter basis than smaller lower return prey such as
lagomorphs, waterfowl, most fish, mollusks, or acorns. This model also posits that highly ranked prey will
always be pursued when encountered, and the decision to pursue lower ranked prey is a function of the
abundance of high ranked prey (Pyke 1984:530; Smith 1983:628). Thus, lower ranked resources are only
included in the diet if the abundance of (or access to) higher ranked resources declines. When such a
dietary restriction happens to human foragers, foraging efficiency decreases and a widening of the diet
breadth typically occurs. Following this logic, the ratio of larger to smaller taxa within faunal assemblages
is typically used as a proxy measure for levels of foraging efficiency.
Resource intensification is defined as “a process by which the total productivity per areal unit of
land is increased at the expense of a decrease in foraging efficiency” (Broughton 1994a:501). Evidence of
resource intensification in past human societies is generally identified as an overall decrease in the
abundance of large prey species relative to small prey species frequencies noted within archaeofaunal
assemblages. This dietary shift is typically associated with dense populations coupled with an increased
investment in the technologies necessary to exploit the amplified amounts of old or new food items in more
cost-effective ways (Basgall 1987; Cohen 1981).
Population reconstructions of pre-contact California suggest the population living here to be
among the highest in North America (Baumhoff 1963; Cook 1955; Kroeber 1939). The ability of this
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demographic phenomenon to exist in the absence of agriculture has been attributed to the adoption of
intensive acorn storage economies during the Late Holocene (Basgall 1987; Bean and Lawton 1977; Heizer
1958; Kroeber 1925; Meighan 1959). Baumhoff (1963) was the first to seriously consider the relationship
between carrying capacity and available food resources in California, and proposed a unique acorn-gamefish adaptation for groups that lived along the Sacramento River and its tributaries within the north-central
areas of the state.
Models of prehistoric indigenous subsistence strategies indicate that there has been a decrease in
foraging efficiency over the Late Holocene for California (Basgall 1987; Beaton 1991; Broughton 1994a,
1994b, 1997, 2002; Broughton and Bayham 1993, 2003; Cohen 1981; Craw 2002; Hildebrandt and Jones
1992; Hildebrandt and McGuire 2002; Pierce 1988; White 2003). Many reasons why diet breadth
expansion occurs in California have been suggested. The most common reasons are a decrease in the
availability of large prey due to increased exploitation by rising human populations (i.e., harvest pressure,
demographic forcing); costly signaling; decrease due to environmental change; or a combination of these
factors (Rosenthal et al. 2007:159-163). Although a limited number of resource intensification models have
been developed for northern California and the Central Valley, few have been developed for the study area.
Two resource intensification studies that specifically apply to the lower Sacramento Valley were produced
by Broughton (1994a) and Craw (2002).
In 1994, Jack Broughton conducted a coarse-grained study grounded in optimal foraging theory.
Basing his research on previously published results from legacy collections, Broughton was one of the first
researchers to attempt to systematically evaluate subsistence patterns in the Sacramento Valley. Using the
prey choice model he compared faunal data collected from nine archaeological village middens
representing Early, Middle, and Late period sites located within the Sacramento River Valley; three of
these sites, SJO-68, SAC-145, and SAC-329, are located within the study area (data from SAC-329 is also
being used in this thesis). Using a series of quantitative indices of relative abundance, Broughton measured
the diachronic changes of artiodactyls against lagomorphs; artiodactyls against anadromous fish; and
anadromous fish against freshwater fish between the sites. His conclusion was that over the past 4,000
years, a trend of increasing reliance on smaller faunal resources exploited by inhabitants of the Sacramento
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River Valley. He explains that Late Holocene archaeological faunas from the area document dramatic
declines though time in the abundance of medium and large mammals relative to small resident fishes
despite seasonal or spatial variation (Broughton 1994a:510). However, this conclusion is not wholly
supported by his data.
Most of Broughton’s indices were consistent with a decline in optimal foraging, however, the
artiodactyl to lagomorph index failed to show a clear temporal trend (Broughton 1994a:507). If his premise
is accurate, then a statistically significant increase in lagomorphs should be seen in the archaeofaunal
record. But it is not. Complicating the issue is his exclusion of small mammal data that could have had
significance. Squirrels which compose 31 percent of the mammal assemblage and carnivores which
comprise ten percent of the total mammal assemblage (many of which were coyote remains) were not
compared to artiodactyls (Broughton 1994a:505).
Another inconsistency relates to the fact that four out the nine sites used ¼ inch screening methods
to recover archaeological data and that faunal remains from SJO-68 were recovered without a systematic
approach (Broughton 1994a:504, 506). Broughton attempts to compensate for the inconsistency in
collection methods by stating that because the relationship between time and the mammal/fish index is
“linear and negative (r= -0.85, P=0.07)…variation in recovery methods does not underlie the temporal
trend in proportional representation of mammals and freshwater fishes” (Broughton 1994a:507). This does
not appear to be the case. An examination of Tables 2 and 3 reveals that the sites having the most fish
remains are those that employed ⅛ inch screening. Further, these tables show that three out of these four
sites which used ⅛ inch screening are Late Period sites while all four of the Middle Period sites used larger
¼ inch screens. It is well known that most fish remains require fine-gauged screening methods or flotation
for recovery (Reitz and Wing 2004:120). Without such procedures, there is likely to be a significant bias in
taxonomic recovery. Thus, when the differential recovery methods are considered in conjunction with the
mean occupation date, it is no wonder that it appears that fish remains increase over time relative to the
amount of mammal remains. Further, the majority of Late Period sites are located in the lower portion of
the Sacramento Valley which is dominated by aquatic habitats while the majority of the Middle Period sites
are located in the upper Sacramento Valley which is dominated by oak woodland and grassland habitats.
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As typical of study area sites, many of the sites Broughton sampled exhibit dates spanning several
different cultural periods. For example, deposits at GLE-101 represent over 3,000 years of occupation from
the Early Period through the Late Period while the record at SAC-145 represents almost 2,000 years of
occupation from the Middle Period through Euro-American contact at the end of the Late Period
(Broughton 1994a:506). As reviewed in the previous chapter, for at least the lower portion of the
Sacramento Valley, significant changes in climate occurred within the area over the last 4,000 years. The
Early Period was generally warm and dry while the Middle Period was generally cooler and wet. In the
Late Period, the climate fluctuated between the warm and dry MCA and the cooler and moister LIA. These
changes would have affected vegetation patterns on land and did affect water flows in the Sacramento
River. The effects of these changes would have affected floral and faunal distributions and abundance (e.g.,
primary production). By averaging the occupation spans and creating a mean date of occupation for each of
the sites, on top of collapsing the faunal remains into one assemblage for each site, Broughton essentially
removes each faunal component from its context and therefore from its temporal significance. Without
contextual reference, additional conclusions regarding “adaptively meaningful” environmental or
technological implications cannot be drawn from the data with any certainty.
Species availability across space is also not fully considered. Four different habitats are identified
for his study area, freshwater marsh, grassland, oak woodland, and riparian forest (Broughton 1994a:503).
Broughton states that no matter a site’s location “artiodactyls and freshwater fishes are available within the
Sacramento Valley floodplain year-round” (Broughton 1994a:508). Although there is truth in this
statement, as seen in Chapter Two (Table 3), freshwater fishes (i.e., minnows and cyprinids) are not found
in the same abundance in the riparian woodland (fast water) habitat as they are in the freshwater marsh
(slow water) habitat. Artiodactyl taxa also differ across habitats. Tule elk could be encountered in the
freshwater marsh, grassland, and riparian woodland, deer in the riparian woodland and grassland habitats,
while pronghorn was only found in the grasslands (see Table 2). As a result, catchment areas would have
provided unique subsistence opportunities for past inhabitants. Further, the territorial circumscription
evident in ethnographic reconstructions (see Chapter Three) would have precluded equal access to all
habitats for certain populations.
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Despite its shortcomings, Broughton’s (1994a) study stands as one of the only studies readily
available for the Sacramento Valley that provides a coarse grained regional model useful for developing
more fine grained subsistence analyses. One such example is Craw 2002.
In 2002, California State University, Sacramento (CSUS) student Maggie Craw preformed a
quantitative analysis using the prey choice model for a single site located on the Sacramento River, SAC29. Craw’s study was an intrasite comparison temporally confined to the Late Period. Her results identified
significant diachronic changes in the abundance of artiodactyls relative to birds and fish, anadromous fish
to resident fish, and adult artiodactyls to subadult artiodactyls between Phase I and Phase II components. A
slight decrease in artiodactyl remains relative to all smaller animals was also indicated through a 10 to 20
percent decrease in artiodactyl use relative to birds (largely waterfowl) and fish (both anadromous and
resident species). Further, an increase in the amount of subadult artiodactyls over time indicated an increase
in harvest pressure for these taxa. In contrast to the above findings, the anadromous fish/resident fish index
showed an increase of approximately 11 percent over time.
An interesting result of Craw’s study was the lack of turtle remains in the components she
analyzed. Whether this was due to observer error or absence, this result is odd for a site located in a riparian
woodland habitat. Western pond turtles are small reptiles that prefer riparian woodland and freshwater
marsh habitats. Their remains are a common component in zooarchaeological assemblages associated with
these habitats over time. Ethnographic evidence also supports the exploitation of this species for
subsistence within the study area (Gifford 1933:139; Lightfoot and Parrish 2009:329). Thus if their absence
from the SAC-29 faunal assemblage is not in error, the lack of this small-bodied, easily captured resource is
in contrast with her finding of increased resource intensification during the Late Period.
In general, the shortcomings of Craw’s (2002) study relate more to the potential for further insight
rather than flaws in methodology. Craw did the lion’s share of the work by separating out units with datable
components from hundreds of samples and identifying the remains. Her statistical analyses are adequate
and the results are generally consistent with Broughton’s findings, supporting the conclusion that there is a
general decrease in foraging efficiency within the region over time. Her choice to include data relating to
age class among the artiodactyls in order to elucidate harvest pressure has interesting implications and does
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well to support her conclusions of intensification by adding a level of analysis that is not always possible in
less robust samples. A more in- depth analysis that considered additional influences on the faunal
assemblage, such as site catchment and the effects of environmental change, could have provided further
insights into foraging efficiency at SAC-29. Such insight is something I hope to achieve in this thesis on an
intersite level by developing a subsistence pattern based on the interplay between catchment area, taxon
habitat preference, and procurement method.
Contrary Evidence
A small set of current studies have found evidence contrary to the general trend of decreased
foraging efficiency in the northern Central Valley for the Late Period. These studies (e.g., Furlong 2004;
Taite 1999; Valente 1998; White 2003) have revealed that after 1,400 B.P. there was a rise in large game
harvesting, particularly in artiodactyls (Broughton 2002:52; Rosenthal et al. 2007:162). This phenomenon
is referred to the “artiodactyl spike.” Locations where this phenomenon has been identified include
Missouri (Wolverton 2005), the Wyoming Basin (Byers et al. 2005), southern Arizona (Bayham 1982),
Nevada and northwestern Utah (Broughton and Byers 2004), Northeastern California (Broughton and
Bayham 2003; Holanda 2000), and the upper Sacramento Valley (Furlong 2004; White 2003). Reasons for
the “spike” have not yet been successfully teased out of the archaeological record and several explanations
have been put forth. The most common explanation is that harvest pressure caused distant, less depleted
deer patches, such as those located in the cultural buffer zones of the oak woodland habitat to be
increasingly targeted. However, it must be noted that the “artiodactyl spike” largely refers to an increase in
deer and not artiodactyls in general (White 2005:27-28); in fact, tule elk virtually vanish from the Late
Period faunal assemblage in Broughton’s Emeryville example (Broughton 2002:52). Additional
explanations are technological change, such as the introduction of bow and arrow technology, fire
management, the increased use of coordinated mass capture techniques, and male prestige (and therefore
increased individual fitness) through hunting prowess (Broughton 2002:52; Hildebrandt and McGuire
2002; Rosenthal et al. 2007:162; White 2005:27-29). The last explanation for the “artiodactyl spike” is
simply that deer populations rebounded due to the onset of the cool/moist climatic conditions which
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enhanced primary productivity after 400 B.P. (e.g., Broughton and Bayham 2003; Byers and Broughton
2004; Byers et al. 2005; Holanda 2000). Documentation of the positive effects of increased precipitation
and cooler temperatures among modern artiodactyl populations has been documented for elk, pronghorn,
bison, mule deer, and bighorn sheep in a variety of environments across the west (Byers and Broughton
2004:238). Thus with an increased population, successful hunting encounters would have increased,
perhaps to an extent which allowed hunters to select prey based on size and age (e.g., antler size and tine
number) for individual prestige.
No matter the cause of the “artiodactyl spike” the tenants of optimal foraging theory dictate that an
increasing abundance of large game on the landscape should result in proportionate increases in large game
hunting (Byers and Broughton 2004:243). How this plays out for the lower Sacramento Valley will be
explored later in this thesis.
Summary
Environmental change is viewed as providing an essential baseline from which to understand
variation in the human record. The increased investment in plant resources, social complexity, new
technologies, and exchange networks reported for the Late Period suggests individuals in the study area
may have been struggling with maintaining fitness in an environment where climatic fluctuations and
economic intensification was causing foraging behavior to be less optimal than before. If intensification
models, such as those presented by Broughton (1994a) and Craw (2002), characterize subsistence change in
the Lower Sacramento Valley, then it follows that patterns of increasing diet breadth (i.e., resource
intensification) should be recognized in the differences between temporally discreet faunal assemblages.
Based on the analyses carried out by Broughton (1994a) and Craw (2002), it is likely faunal assemblages
examined in this thesis will also display statistically significant changes in diet indicative of resource
intensification over space and time. By examining the influence additional factors, such as site catchment,
animal habitat preferences, procurement technologies, and climate, may have had on resource availability,
it is hoped that some of the data gaps left by preceding investigations will be filled. To achieve this goal,
certain sets of assumptions will need to be made which future researchers may or may not find fault with.
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These assumptions and the particular methods of how to accomplish this goal are discussed in the
proceeding chapter.