JOURNAL
OF ANTHROPOLOGICAL
ARCHAEOLOGY
1,
56-97 (1988)
A General Explanation of Subsistence Change: From
Hunting and Gathering to Food Production
RICHARD W. REDDING
Cranbrook Institute of Science, 500 Lone Pine Rd., P.O. Box 801,
BloomjIeld Hills, Michigan 48013
Received March 27, 1985
No widely accepted, general model for the origin of food production has
emerged despite the effort expended. It is argued that this is due to three defects
that most of the published explanations share. After a consideration of these
defects and several concepts (e.g., carrying capacity, population growth in humans, selective milieu for human behaviors that limit reproduction, evolution of
hunter/gatherer subsistence tactics, and the evolution of tactics versus strategies),
an explanation for the origin of food production is presented. The explanation
assumes that local populations of hunter/gatherers grew and stressed the resource
base causing these groups to adopt tactics to relieve the stress. The alternative
tactics were emigration, diversification of the resource base, and storage. If the
population continued to grow, either behaviors that limit reproduction became
advantageous or a change in subsistence strategy to food production had to occur.
Behaviors that limit reproduction would have been favored in areas in which
fluctuations in the resource base were, relatively, more predictable, less frequent,
and less severe. Food production would have been favored in areas in which the
fluctuations were, relatively, less predictable, more frequent, and more severe.
Although the explanation is not formally tested, a number of implications of the
explanation that may be tested with archaeological data are noted, and the explanation is examined in the context of some archaeological data. Q 1988Academic
Press, Inc.
INTRODUCTION
The development of food production marked a qualitative change in
human subsistence behavior that had far reaching consequences for cultural evolution. Hence, the documentation
and explanation of this shift
has been an important focus of archaeological research. The descriptive
and theoretical literature on the subject is voluminous, but despite alI the
effort expended no widely accepted, general model exists to explain the
origin of food production. I will argue that this is due to a number of
fundamental defects shared by most of the proposed explanations, and by
confusion over what is being explained. I will present a synthetic model
56
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Copyright
8 1988 by Academic
Press, Inc.
AII rights of reproduction
in any form reserved.
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57
of human subsistence behavior that attempts to explain changes from
hunting and gathering through the development of food production; subsuming an explanation for the origin of food production.
The approach I will utilize needs to be made explicit and discussed
before proceeding further. I will use a Darwinian evolutionary paradigm
similar to what Rindos (1984:74) has called Cultural Selectionism, but the
approach, contrary to Rindos’, will emphasize a search for the selective
pressures that operated on human subsistence behavior. I will not try to
defend the use of a Darwinian approach to changes in human behavior. A
number of authors have already detailed selectionist models for application to humans and discussed their utility (e.g., Alexander 1979a, 1979b;
Boyd and Richerson 1985; Cavalli-Sforza
and Feldman 1973, 1981;
Durham 1979, 1982; Flinn and Alexander 1982; Irons 1979; Rindos 1984;
Wilson 1978). Those familiar with this literature will have realized that
this list represents a diversity of opinion on how to model cultural evolution using a Darwinian paradigm. The model of Durham (1979, 1982),
most closely resembles the one I, implicitly,
use in this paper.
Previously published explanations for the origin of food production
have frequently depended on a “prime mover” (e.g., population growth,
environmental
change) as the mechanism for change or while recognizing
the importance of a number of factors, stressed one as primary. It is
unlikely that a single selective pressure is operating on any behavior,
instead a number of selective pressures interact to produce a selective
milieu. It is probably impossible to identify all the selective pressures on
a behavior and the variants of the behavior that they favor. The model I
will develop identifies the major selective pressures and suggests how
they might interact. However, some sources of pressure, seen as amplifying or subsidiary, will be ignored in order to simplify the model (e.g.,
see the discussion of sedentism and environmental change in the General
Comments section).
PREVIOUS
WORK
ON THE ORIGIN OF FOOD PRODUCTION:
A SUMMARY
Before the explanation and model can be presented, and in order to
justify the approach I will utilize, a quick review and critique of the
published explanations for the origin of food production must be undertaken.
The concensus among people working on the problem of the origin of
food production, as expressed in the most recent, general, multicontributor volume on the subject (Reed 1977a), is that food production devel-
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oped independently in four or five areas of the world. Research in each of
these centers has concentrated on four questions:
(I) What were the plant and animal species used in the local development of food production?
(2) When did food production appear in the area?
(3) How did domestication occur?
(4) Why did humans shift from food collecting to food production?
The answer to the first question simply requires the identification
of domesticates from sites. The second is more complex and requires more
than the simple dating of the earliest evidence of domestication. The third
question requires a description of how plants, animals, and humans interacted resulting in domestication.
Parts of a recent work by Hesse
(1982) examines this question for animals and recent works by Rindos
(1980, 1984) presents a new approach, primarily for plants, to this question. The fourth question is the real challenge to researchers requiring the
development of predictive models based on ultimate explanations. What
were the selective pressures that favored food production? This is the
question with which I am concerned in this paper.
Numerous explanations have been offered to answer the fourth question. All of these explanations, except those employing vitalism as a
mechanism, use, implicitly
or explicitly,
some evolutionary paradigm.
But, these models vary considerably in complexity, theoretical sophistication, and intended generality. The major effort to understand the origin
of food production has been directed toward the Near East, and all the
explanations have, in general, focused on the origin of food production in
the Near East. All of them, however, have been applied to other areas of
the Old World as well as the New World centers. Some of the explanations have been offered as formal models or with testable implications
(e.g., Binford 1968), while others have been offered as assertions (e.g.,
Moore 1982). The explanations that have been proposed are diverse and
any classification will inevitably do a disservice to some one; however,
with this caveat in mind, the proposed explanations can be divided into
six types based on mechanism:
(1) Those explanations in which no cause is cited and the origin is
seen as the result of human inventiveness (e.g., Braidwood 1963; Carter
1977).
(2) Those in which climatic change is the prime mover. These include the Oasis model (Childe 1952) and a modified nuclear zone model
(Wright 1968).
(3) Those in which population growth is the primary mechanism
(e.g., Smith and Young 1972; Cohen 1977a, 1977b).
(4) Those in which population growth and change or variation in
GENERAL
EXPLANATION
OF SUBSISTENCE
CHANGE
59
climate interact to effect domestication (e.g., Binford 1%8; Hassan 1977,
1981; Hesse 1982).
(5) Those in which food production is seen as the end result of the
development of an evolutionary relationship (Rindos 1984).
(6) Those in which no mechanism is directly identified but the origin
of food production is seen as the result of the operation of a number of
variables (Redman 1978; Moore 1982).
Vitalistic explanations, type 1, are not testable and are unacceptable (Binford 1968:322). No models of the other types have been successfully
applied to all the centers of domestication, but only the Oasis explanation
has been rejected for all the centers of the world. Probably the most
widely accepted explanations are those based on population growth, type
3, and Binford’s edge-zone model, one of the type 4 explanations. Models
based on population growth have been criticized on theoretical grounds
(Bronson 1977; Reed 1977a; Rindos 1984). Flannery (1969) applied Binford’s model to the Near East, but did not formally test it. However,
enough people were persuaded by Flannery’s article that Flannery was
later forced to warn: “although it [Binford’s model] has won almost
frightening acceptance among some of my colleagues, it is still unproven
and highly speculative” (Flannery 1973:284). In the same article Flannery
(1973:296) notes that while Binford’s model might be applicable to South
America, it could not explain the origin of food production in Mesoamerica, because population densities prior to the origin of food production
were very low.
A new approach to explaining why humans shifted from hunting and
gathering to food production has recently been offered by Rindos (1984).
This is a generally sound and useful treatment of the problem. I do not
intend to review Rindos’ work here, but I would like to examine some of
the assumptions and assertions he makes as they affect the discussion
here. Rindos suggeststhat food production arose as a result of the development of a mutualistic relationship between humans and plants
(/animals). He sees why this mutualism developed as an irrelevant question.
Why humans began to establish coevolutionary relationships with plants is a question without real meaning. We might as well ask why certain ants established
coevolutionary relations with fungi or certain birds with specific fruits. The relationships were established as a result of the maximization of fitness in a given
situation in time and space; they were neither inevitable nor desireable, but merely
happened. (Rindos 1984:141)
For Rindos, food production arose as the result of the development of
coevolutionary interactions.
I disagree with this position. Fitness is relative; hence, an increase in
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the fitness of one form must be at the expense of the fitness of another.
The development of mutualistic behaviors, if they increased fitness, must
have come at the expense of other forms of behavior; the concept of
fitness only has meaning in a selective milieu. Hence, selective pressures
must have been operating that favored the establishment of mutualistic
behaviors. What does the mutualism (even in its earliest stages) provide
that gives the behavior an advantage for both symbionts in competition
with other members of their population: is it food, safety, nesting sites,
etc.? The question of why involves identifying the selective pressures
operating and which behaviors they favored. If we accept Rindos’ model
as how food production arose, we must still examine why humans and
plants developed and maintained a mutualistic relationship.‘,”
Rindos in
other sections of his (1984) book implicitly recognizes the validity of the
search for the operating selective pressures (e.g., pp. 178-189, p. 196). To
assert that the why is unimportant because food production is the result
of advantages resulting from mutualism ignores what may be a source of
useful insight into the forces affecting human behavior.
A further problem with the work of Rindos, as affects the discussion in
this paper, is that his model offers no explanation for why food production
developed in some areas and spread out from these centers. Based on the
model the only answer would be that the centers are where mutualism
first developed. However, the selection for and spread of a new trait first
requires the appearance of that trait. But whether that trait spreads in the
population and how quickly it spreads depends upon the pressures favoring and opposing the variant. Hence, again we see the value of seeking
selective pressures: factors that affect the relative fitness of variants.
GENERAL
PROBLEMS
OF THE EXPLANATIONS
The purpose of this section of the paper is not to review published
criticism of the various explanations. What is presented here is an overview of the specific problems that have not previously been discussed.
The failure of any of the proposed explanations to survive testing in more
than one area, or to be generally accepted, is due, I believe, to three
defects. Some of the proposed explanations contain all three of the defects; others contain only one; Rindos’ explanation contains none of these
defects.
Defect
1
The first defect with the published explanations
* See Notes section at end of paper for all footnotes.
is that they focus on the
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development of food production. Most of them describe some preceding
and succeeding changes in human subsistencebehavior, and acknowledge
that the ones they identify are related to the development of food production (Christenson 1980; Cohen 1977b; Earle 1980; Flannery 1968,
1969), but only Flannery (1%9), Cohen (1977b), and Hassan (1981) really
attempt to fit one of the changes into their model. The origin of food
production is part of a continuum of change in human subsistence tactics
and strategies. Other parts of this continuum, containing changes that
occurred before and after the shift to food production, should provide
insight into the selective pressures operating on human subsistence, and,
if we are to develop a general explanation for the origin of food production, then these changes should also be predicted by the explanation. The
goal of this paper is to explain changes in human subsistencefrom hunting
and gathering through food production.
Defect
2
Most of the explanations for the origin of food production have started
with the given that some plant(s) and/or animal(s) were domesticated in
some area, and then sought to explain why (an important exception to this
generalization is Binford’s (1968) treatment of the problem). This approach led to explanations that were region specific: when applied to data
from other areas they tended to fail. This approach is too limited and
ignores several important questions that need to be addressed by any
general explanation. Two of these questions are: why here, and why not
there? These two questions rarely have been addressed (for an exception,
see Pryor 1986) and when they have, the answer proposed has been the
distribution of potentially domesticable plants and animals or suitability
of the area for agriculture. Rindos (1984:91 and implicitly on p. 20) denies
that these are useful questions. However, again, by identifying the selective pressures that lead to food production and exploring why they did not
affect the populations in some areas, we can gain insight into the general
pressures operating on human subsistence.2 Another question that any
general explanation must consider is why did food production spread?
Most workers seem to assume that once it arose, food production spread
because it was a superior subsistence strategy compared to hunting and
gathering. Given work on hunter/gatherer labor investment in subsistence
(e.g., see part II of the volume edited by Lee and Devore 1968), it is
unlikely that such an explanation for the spread of food production is
viable (Pfeiffer 1976:27). Rindos (1984:271-284) has offered a model for
the spread of food production based on differences in fluctuations in
carrying capacity between populations using food production and those
using hunting and gathering. Food production spread because in the local
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environment individuals who adopted it raised more and/or more fit offspring, and as an initial research position I would suggest that the selective pressures that favored the spread of food production are identical or
very close to those that lead to its origin.
Defect 3
The third defect actually has two related aspects. First, most of the
published explanations assume, implicitly or explicitly, that decisions to
limit population or change food procurement strategy are made by the
larger group for the good of the group, when in fact such decisions are
characteristically
made by individuals or small groups of closely related
individuals.
This reliance on what evolutionary biologists have called
“group selection” becomes important when it is assumed that individuals
reduce their fitness for the good of the group. Second, most of the published explanations assume that food production is, and has always been,
an alternative to gaining resources from hunting and gathering. Hence,
the function of food production at its earliest stage was to replace food
resources gained by hunting and gathering. (I will propose a bridging
function for the earliest stages of food production-see
the first point
under General Comments and under An Explanation
and Model.) The
potential difficulties encountered when group based, functionalist explanations are confused with evolutionary explanations are apparent in recent discussions of female infanticide (Hawkes 1981; Dickemann 1981).
Using Binford (1968), Flannery (1969, 1973), and other works with a
demographic emphasis as a starting point and stimulus I have developed
an explanation for changes in human subsistence tactics and strategies
from hunting and gathering through food production that avoids these
defects. The explanation is designed to be universal: the implications
derived from it are testable in any area of the world. In order to present
this explanation in a clear, intelligible fashion I would like to precede it
with a discussion of some concepts, definitions, and assumptions. Following the presentation of the explanation I will briefly discuss and restate some important points that are not explicitly made in its presentation
and then discuss some predictions that may be used to test the explanation. Finally, I will briefly illustrate the model’s potential by discussing it
in the context of some of the archaeological data from the Near East.
Formal testing will not be undertaken in this paper.
CONCEPTS,
Carrying
DEFINITIONS,
AND ASSUMPTIONS
Capacity
Population
biologists
and ecologists have developed the logistics model
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63
to describe population growth. The model describes growth as the interaction of two independent parameters; both of these parameters are area
specific. The first parameter is the intrinsic rate of increase (r). The r
value for an area is derived by subtracting the death rate from the birth
rate. The carrying capacity (K) of an area is the point on the logistic
growth curve at which further increase in a population in a given area is
not possible because of environmental
resistance. The parameters are for
a population in a particular environment and are partially dependent upon
the behavior of the animal. Hence, selection may act on the population to
alter these parameters.
In borrowing the logistic model from ecologists, anthropologists
have
significantly altered the definition of carrying capacity. For anthropologists, carrying capacity is the level of population that an area can support
with a given subsistence technology without degrading the environment
(Allan 1949; Cook 1972; Hayden 1975). Using this definition anthropologists and archaeologists have expended considerable effort in trying to
calculate the carrying capacity for a group or an area (Allan 1949; Meggit
1962; Lee and Devore 1968: 11; Sahlins 1968; Rappaport 1968; Washburn
1968; Casteel 1972; Hassan 1973, 1976, 1981). These efforts have been
heavily criticized and the value of the concept of carrying capacity has
been questioned (Street 1969; Hayden 1975). However, the difftculties are
a direct result of the attempts by anthropologists
to operationalize
the
concept; as a theoretical concept carrying capacity is useful (Richerson
1977; Glassow 1978; Hassan 1981:166).
Human
Populations
Expand
and Stress
Their Resource
Base
Proponents of population pressure as a causal mechanism for the origin
of food production assume that human population in an area may increase
until it exceeds carrying capacity. Hence, human populations may stress
their food resources, and when they do, adaptations will emerge that
allow the population to continue to grow. I would prefer to structure this
argument in a slightly different fashion. Human population in an area may
increase but as it approaches K an increasing amount of the available
energy will be put into maintenance of the population and a decreasing
amount into reproduction.
Hence, theoretically
the population should
never exceed K. Under these circumstances as the population approaches
K selection will favor individuals who utilize tactics and strategies that
allow them to put relatively more resources into reproduction, either by
increasing their share of the available resources or by exploiting altemative resources.
Even given this restatement of the position the question remains
whether human populations ever approach the carrying capacity of an
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area. Many researchers oppose this position: these individuals argue that
human populations are maintained below carrying capacity by internal
social, or cultural, controls that function to regulate the population so
they do not stress their resource base. These internal regulatory mechanisms include a number of behaviors that affect fertility (e.g., delayed
marriage, abstinence, prolonged lactation, etc.) and mortality (e.g., infanticide). An extreme proponent of this view has argued that all human
groups, living and prehistoric, and most primates, regulate their population far below carrying capacity and these groups have been rarely, if
ever, stressed by food shortage (Hayden 1975). A basic assumption of
Binford’s (1968) explanation for the origin of food production is that late
Pleistocene populations of hunters and gatherers were in equilibrium with
their environment and were being maintained below carrying capacity by
behavioral regulatory mechanisms.
The argument between the proponents of population pressure on subsistence resources as a force in cultural evolution and proponents of the
position that human populations rarely stress their resource base because
they are internally regulated occupies a considerable amount of the space
devoted to theory in Origins of Agriculture (Reed 1977a). In a summary
statement Reed (1977b:890) suggests, concerning the controversy, “. . .
no general consensus emerges . . . and no general conclusion is possible
at this time.” Proponents of the position that human populations have and
do homeostatically
regulate their numbers below carrying capacity with
behavior usually cite the theoretical work of some biologists, particularly
Wynne-Edwards (1962, 1963, 1964, 1965, 1970), studies by demographers,
and studies of extant hunting and gathering groups.
Cohen (1977b) has reviewed much of the pertinent data and arguments
that were published prior to 1976. He criticizes the use of demographic data
from extant populations of hunter/gatherers (Cohen 1977b:42-52) and examines data from the human fossil record that suggest many of the parameters in the logistic growth model had quite different values in the
Pleistocene than they do at present in any human population (Cohen
1977b:52-56).
First, I would like to point out that much of the biological theory, such
as that of Wynne-Edwards, based on the group selection paradigm, has
been discredited (Williams 1966; Wilson 1975): group selection is believed
to be unable to overcome the effects of individual selection except in very
rare circumstances (Alexander 1971; Fox 1979). Second, I would like to
update briefly some of the criticism provided by Cohen. Recently, demographic models of the growth of human population have been developed
that suggest that even at a low r a single pair could multiply to a population exceeding the present world population in only a few thousand years
(Hassan 1981:125-144). From these models it is concluded that Pleisto-
GENERAL
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65
cene human populations must have been regulated (Hassan 1981: 143).
But these models generally utilize an r that is the highest one might expect
in the environment. The average value of r over the Pleistocene must have
been considerably less, because, even as Hassan admits (1981:14&142),
r may be negative (resulting in a decline in population) in some areas for
periods of time and may fluctuate in any area dramatically.
A juvenile
mortality rate of 50% may result in a decreasing population (Hassan
1981:138). Hassan cites observed rates for nonindustrial
populations of
between 30 and 50%. Hence, these models probably reflect a “best case
scenario” and are not good estimates of real population growth during the
Pleistocene. Bates and Lees (1979:281) have questioned the use of demographic data from modern hunter and gatherer groups as models for the
demography of prehistoric populations because of the lack of time depth
and lack of regional focus. Wolpoff (1980:284), working with deciduous
dentitions from the Pleistocene, has concluded that prehistoric hunter/
gatherers had short birth spacing and high mortality rates; a combination
he points out that is not found among any living hunter/gatherers. Wolpoff
also suggests that the demographic balance found among modern hunter/
gatherers, which generally inhabit marginal environments,
results from
marked improvement in infant and adult survivorship that came with the
Late Pleistocene and Holocene adaptive changes. Finally, Cohen and
Armelagos (1984) have recently edited a book concerned with paleopathology in skeletal samples associated with the development of food production. Cohen and Armelagos conclude (1984597):
In sum, these data provide some suggestive evidence but no clear indication of
declining health and nutrition among later hunter-gatherers as a population pressure model might suggest. Conversely, the data may show a declining workload
among late hunter-gatherers, but otherwise, with the exception of the Benfer
study, they provide little indication of any general, progressive improvement in
hunter-gatherers’ lifestyles and economic homeostasis.
I think Cohen and Armelagos are correct in their summary. But with the
restatement made at the beginning of this section on how population
pressure would work as the population approached K, one would not
necessarily expect to see an increase in mortality or pathology in adults;
what one would expect is decreased fertility and a shift in the age curve.
Another point needs to be made in this section. Confusion exists over
the relationship between population density and its relation to K. For
example, Hassan (1981:219) states:
I do, however, think that the increase in world population to g-10 million persons
by the end of the Pleistocene and the colonization of most of the world biomes by
the close of the Pleistocene might have served in some cases as a precondition,
rather than a cause or triggering mechanism. Flannery (1973) notes that agriculture
emerged in Mesoamerica in areas where population density was low. In the Nile
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Valley, where population density was high, food production lagged three millennia
behind that of Southwest Asia and was in the most part stimulated by outside
contacts. . .
Clearly Hassan assumes that a high density is correlated with a population
approaching K. But an area may have a high carrying capacity, under a
given subsistence strategy and tactics, and support a relatively high density without the population approaching K. In another area, with the same
subsistence strategy and tactics, the carrying capacity may be low and
have a relatively much lower density that is at or near K. Just because the
population density was low in Mesoamerica is no reason to assume that
the population was not stressing the resource base, whether it was or was
not at or near K. And, just because density around the Nile Valley was
high is no reason to assume that the population was at or near K. K varies
from environment to environment and with the strategy and tactics being
employed.
An important question is when did humans begin to approach K? This
question does not have a single answer because values for r and K must
be determined and these, as noted above, vary from area to area. A
further complication comes from the fact that K is also dependent on the
subsistence tactic and strategy being employed by the group occupying
the area. What we can say is that human population, on a world-wide
basis, appears to have grown throughout the Pleistocene and appears to
have swung up significantly starting between 40,000 and 20,000 years ago
(for a review of the data, see Cohen 1977b; Hassan 1981:196-203).
Do Behavioral Population Regulation Mechanisms
What Selective Pressures Might Favor Them?
Exist in Humans?
Two types of population control mechanisms may exist in humans:
physiological and behavioral. Physiological controls depend upon external stress to trigger them and are related to environmental
stress. These
are the mechanisms that cause a population to decline or stabilize as it
approaches K. Physiological controls and mortality acted throughout human evolution limiting growth rates as carrying capacity was approached,
probably contributing to a low r during the Pleistocene. It is behavioral
controls that are of interest to use here for they are the controls that are
proposed by many workers to have limited population growth in humans
and prevented populations from ever approaching K.
The observation that many natural populations of animals appear to be
stable at low densities contributed in a fundamental way to WynneEdwards’ development
of a theory of social regulation of population,
which assumes that selection can occur at the level of the group. Also
GENERAL
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67
fundamental to the development of Wynne-Edwards’
theory were observations of behaviors in birds and mammals that appeared to be detrimental to the reproductive success of the individuals exhibiting the behavior.
As noted above the group selection paradigm has been rejected by most
ecologists and evolutionary biologists, and the observed stability in many
populations has been attributed to a number of factors that can cause
density-dependent
increases in morbidity and mortality (e.g., Williams
1966:234-246; McLaren 1971:14-U; Ricklefs 1979514-528). The apparently detrimental
behaviors have, when examined, been explained in
terms of maximizing
an individual’s
inclusive fitness (e.g., Lack 1968;
Sherman 1977; Emlen 1978; Low 1978). Dickemann (1979, 1981) has offered an explanation along these lines for female infanticide in humans.
Clearly some of the behaviors that have been identified as social population regulating mechanisms directly affect demographic variables. But
it does not follow that their presence in a population is due to selection for
limits to population growth. The selective pressures for a given behavior
pattern, like infanticide, may not be based in population control: “If
stability is the result, the pattern may be selected for despite, rather than
because, of this side effect” (Bates and Lees 1979:278). An individual
may utilize a behavior that affects birth and mortality rates in an effort to
limit his/her own reproduction in order to maximize his/her inclusive
fitness. For example, consider non-sex-biased infanticide in humans. Alexander (1974:368) has suggested that infanticide may be advantageous to
an individual under four conditions, two of which are related to food
stress, but only if either the cost to the parent because of an increased risk
of mortality, which may result in a loss of future reproduction, outweighs
benefit to be gained by immediate reproduction; or, addition of another
offspring reduces the potential fitness of the offspring already born (Chagnon et al. 1979:294). Hence, an individual, by engaging in infanticide, may
raise his or her fitness. Similar arguments have been advanced to explain
abstinence and abortion in human groups (Alexander 1974:368). A number of individuals in the population utilizing one or more of these behaviors may produce a stable population.
Two selective milieu can be identified that will result in the maintenance in a population of behaviors that limit population. The first involves
decisions not related to the population approaching K. For example; it has
been argued by several workers (see Hassan 198 1: 147) that a long birth
spacing may be advantageous for hunter/gatherers because of their mobility. Birth spacing may be manipulated by abstinence, prolonged lactation,
induced sterility, induced abortion, and infanticide. Behaviors that act to
limit population based on selection unrelated to the population approaching K are unlikely to result in maintence of the population at a level below
carrying capacity. They may severely reduce the growth rate and, hence,
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have accounted for very slow growth rates in some areas of the world
during human evolution. The second selective milieu involves decisions
made that are related to limits on reproduction
as the population approaches K. For example, infanticide may be used to eliminate offspring
that may reduce the quality of previously born offspring because they are
competing for limited resources (thus diverting food resources from reproduction to maintenance). I suggest that, in the long run, only behaviors
that limit population based on selection related to the population approaching K, result in a population maintained below carrying capacity. It
is the second selective milieu that proponents of the position that human
populations are internally regulated are arguing was important in maintaining densities of Pleistocene and living hunter/gatherers below carrying
capacity; and, such proponents are assuming that internal regulation is
the first strategy or tactic that selection would favor. An individual limiting his or her reproduction in response to some environmental
stress in
an area in which other individuals are reproducing, successfully, at a
higher level because they have adopted a strategy or tactic that alleviates
the stress, must either cease limiting his or her reproduction and adopt the
alternative strategy, or be selected against. Whether one wants to use a
group selection paradigm or a paradigm of selection operating at the level
of the individual, selection should not favor any behavior that decreases
birth rates and/or increases mortality rates until alternative strategies/
tactics that alleviate the stress (and in this scenerio permit an increase in
the population of individuals using the alternative strategy/tactics) have
been exhausted. This is a consequence of selection favoring strategies and
tactics that maximize an individual’s contribution to subsequent generations .
Human Population Growth, on a Regional
Will Vary within and between Regions
Scale, Is Erratic,
and Rates
Population growth in humans, on a worldwide scale, is usually assumed
to have been exponential (Bronson 1977:37; Hassan 1981: 196). However,
this model is unlikely to reflect growth on a regional scale because regional populations are subject to fluctuations due to periods of excessive
mortality, emigration, and random variation in mating success. Population growth in a region is more likely to resemble the curve in Fig. 1
(Bronson 1977:39). Attempts to estimate population growth for some regions have yielded curves similar to Fig. 1 (Renfrew 1972; Johnson 1972;
Butzer 1976%; Schacht 1980:791).
Further, since regions provide a mosaic of habitats and some of these
habitats are more favorable for population growth in human groups using
a hunting/gathering
strategy, groups in different areas of a region will
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
69
FIG. 1. Hypothetical growth curve.
grow at different rates and face different limits on their growth. Some
areas will probably not support population growth in hunter/gatherers,
while other areas will allow for sustained growth near the intrinsic growth
rate (r,.&. What should be the characteristics of areas that would support
the highest sustained growth rates? It should be possible to model population growth in order to determine the factors most important in supporting growth rates. However, lacking such a model at present, we can
only make some general statements on factors that might support high
growth rates by maintenance of a high birth rate or by reduction of juvenile mortality. The most obvious factors would be high food yields per
unit of labor and minimal fluctuations in resource availability. Such areas
would be those that allow exploitation of a variety of habitats: for example, ecotonal situations such as coastal areas or the intersection of mountains and river plains. These ecotonal areas should not be confused with
the marginal areas, postulated by Binford (1968) to be the sites of early
food production. Binford’s marginal areas are on the edges of the natural
habitats of potential domesticates where resource densities, in general,
drop off, marginal areas may or may not be ecotonal.
These points are important for two reasons. First, they indicate that in
an area exploited by hunter/gatherers it may take a long time, even at high
growth rates, for the inhabitants to approach K, if indeed they ever do.
Second, different areas in a broad region, like the Near East or Mesoamerica, may attain populations that approach K at very different
times.
Carrying
Capacity
Fluctuations
and Fluctuations
in Food Resources
in food resources may occur in a number of time frames;
70
RICHARD
W.
REDDING
however, in general, they may be classified as intra- or interannual. It is
the latter, interannual fluctuations, that are important to the development
of the explanation to be presented here. Two types of interannual fluctuations in food resources may be distinguished and each plays a different
role in the explanation. The first type is due to short term, year to year,
variation. These are the types of fluctuations characterized by statements
of deviations from average yields. They are primarily the result of interannual environmental
variation. This is particularly true in semiarid and
arid areas and much less true in coastal areas. Whenever I use the term
“fluctuations”
in the rest of the paper I am referring to year to year
fluctuations. The second type of inter-annual fluctuation is long term and
is the result of long term environmental
change. These are the types of
fluctuations characterized by statements such as “the environment
became increasingly warm and dry.” Long-term fluctuations play only a minor role in the explanation and will be briefly discussed only once more.
The logistics model of population growth predicts that a population
should grow rapidly as it starts to fill up an area, but as the population
approaches K growth should start to slow, and the population should
stabilize at or near K due to density-dependent factors. At the stable point
the population may fluctuate up or down slightly; over time, however, all
increases will be balanced by a decrease and vice versa. For two reasons,
both very important to the model to be developed here, such stability
probably only rarely obtains. First, selection may operate on the behavior
of the animal resulting in an alteration of r or K. Second, the ability of an
area to support a given population exhibits intra- and interannual variation. Hence, if a population is at or near K a down turn in the environment
may place the population above the current carrying capacity of the area.
A long-lived species, particularly one with a long pregnancy and postpartum dependency period, like humans, will be unable to track the intraannual and most of the interannual variation in an area’s carrying capacity.
If the population is unable to track changes in K, then whenever the
carrying capacity is depressed the population will experience increased
morbidity and mortality, which will decrease average fitness compared to
what it would have been without the fluctuations. The severity of the
decrease in average fitness wilI depend upon the severity of the depression of K. Hence, it is likely that a long-lived species will have a population in an area that is below K most of the time due to periodic depressions of K. How low this realized K will be depends upon the nature of the
fluctuations.
Three variables, predictability,
frequency, and severity may be used to
describe fluctuations in annual yields. Predictability
refers to nonrandomness in the occurrence of fluctuations. Frequency is simply a measure of
how often depressions, or super abundances, in resources occur. Severity
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
71
is a measure of the magnitude of fluctuations.
As an example of the
importance of the interaction of predictability
and frequency in the evolution of subsistence strategies and tactics, plant species using a predator
satiation tactic in reproduction appear to have been under strong selection
to develop patterns of reproduction that are longer than the life-span of
their major predator (Janzen 1976).
As pointed out previously only unprecedented fluctuations in carrying
capacity should result in a population being above the K of an area.
Hassan (1981:16&173) extensively discusses fluctuating environments
but concludes that the effect will be to force humans to maintain their
population at a level below the critical carrying capacity, a position that
has been criticized above. Ecologists have developed models of population growth in fluctuating environments but these have, in general, been
designed to examine the relationship between stability and complexity in
communities (e.g., May 1973, especially 109-138; Ricklefs 1979:844-863).
Hassan does not discuss the fact that fluctuations may vary in structure
between areas. Fluctuations in some areas will be more predictable than
in others, in some more severe, and in some more frequent. Hence,
fluctuations have the potential for being a very important factor in the
evolution of human subsistence, as they certainly affect K, and the effect
of these fluctuations will vary from area to area.
An important test of the explanation that I will propose requires the
estimation of the predictability,
frequency, and severity of variations in
an area’s resource base and the comparison of these values among areas
within any region. Colwell(l974)
has developed a measure of predictability in periodic phenomena. Colwell applies it to rainfall data as an estimate of resource availability.
An estimate of the severity of fluctuations
could be derived by the calculation of a standard deviation from, for
example, rainfall data. Frequency is a more difficult parameter to determine. It needs to be expressed as the occurrence of some level of severity
over time. Measures of all three of these parameters are needed in order
to compare fluctuations in resource availability between areas.
HuntedGatherer
Subsistence
Tactics
O’Shea and Halstead in a series of useful and interesting studies (Halstead 1981; O’Shea 1981; Halstead and O’Shea 1982) have suggested that
hunter/gatherer,
pastoral, and agricultural groups when faced with food
shortages use three tactics to relieve stress on the food base. These tactics
are mobility,
diversification,
and storage. O’Shea and Halstead treat
these tactics in a descriptive fashion and are primarily interested in exploring the role of storage in adapting populations to resource failure.
However, these tactics may be thought of in an evolutionary framework
72
RICHARD
W.
REDDING
and viewed as part of a set of alternative solutions to the problem of
resource shortage or failure that are available to hunting/gathering
groups.
Two basic types of movement may be identified. These are intraterritory and interterritory
movements. O’Shea and Halstead are primarily concerned with the first type, but it is the latter type that is central
to the following discussion.
All three tactics represent variant behaviors based on simple hunting
and gathering. When each tactic first appeared in a population it did so
because it had a positive selective value in the environment at the time,
and the behavior spread. After the initial appearance it became part of the
behavioral repertoire and may be viewed as an evolved response. But
remember that each time one of these tactics was utilized it was subject
to selection. Any one of these tactics may be employed in any given year
to compensate for fluctuations in food resources, but long term shifts in
the predominate tactic are responses to directional selection. One source
of such directional selection would be the approach of the population
to K.
Among individuals
using a hunting/gathering
subsistence strategy
movement is probably the tactic that selection would favor first. If a
depression in the food base occurs or as the population in an area approaches the carrying capacity provided by preferred resources, then by
the migration of a number of individuals to an under-utilized
area, individuals in both areas can continue to subsist on preferred resources. Lees
(in Flannery 1973:283) maintains that emigration was probably the most
important mechanism in keeping local population densities low during the
first two million years of human evolution, and by 10,000 B.C. most of the
world was occupied and migration was no longer a viable tactic for reducing local population densities. At times the risk involved in movement
is high, for example when population density is high in surrounding areas
and the occupants of these areas resist emigration, or if the emigrants
must move very long distances; or the cost/benefit ratio for movement
exceeds the cost/benefit ratio for using second and third choice resources.
Under such conditions selection should not favor migration, the tactic
favored should be diversification,
which effectively increases the local
carrying capacity. Diversification
results in an increase in the diet of
second and third choice foods that require more effort per unit of yield
than first choice foods and may lead to intensive use of third choice
resources. Some authors have recognized the importance of diversification in the development of food production (Flannery 1969; Cohen 1977b;
Christenson 1980; Earle 1980; Hesse 1982). Christenson (1980:34-38) and
Earle (19805-18) provide models for diversification based on population
pressure on food resources. At some point return from adding the next
resource, further diversification,
exceeds energy spent, and further diver-
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
73
sification would decrease an individual’s
fitness. At this point storage
could have a positive selective value, if storable resources are available.
Another tactic available to hunter/gatherers to deal with the problems
of approaching K is the use of behaviors, by individuals, that reduce their
rate of reproduction (this tactic is also available to individuals using food
production as a subsistence strategy). But, for reasons suggested earlier,
this tactic will be selected for only when all alternative tactics have been
used and the population is at or near K. Limiting reproduction will have
a positive selective value only when it increases an individual’s
total
reproductive success relative to individuals not limiting their reproduction.
I have treated these four tactics as a sequence because of the increasing
cost of each of the tactics. I would argue that this was the most commonly
occurring sequence. However, it is quite likely that in some areas, under
some circumstances, shifts occurred that were not in sequence.
Pleistocene
Hunter/Gatherers
Were Capable of Food Production
I will assume that hunter/gatherers were aware that if you planted seeds
you could grow plants and that captured animals could be tethered and
fed, maintaining
them for later consumption.3 Extant hunter/gatherers
have a detailed knowledge of their environment
and it is illogical to
assume that Pleistocene hunter/gatherers were ignorant of theirs (Cohen
1977a:138; Bronson 1977:28-29). But the planting of seeds, caring for
them, and the maintenance of animals by hunter/gatherers would require
the expenditure of energy beyond what might be required to obtain the
identical resources by hunting and collecting, and also requires a significant shift in human behavior. Hence, an important question that must be
answered by any explanation for the origin of food production is, under
what conditions would this expenditure of excess energy and behavioral
shift be advantageous?
Tactics and Strategies
Hunting/gathering
and food production may be thought of as two strategies for obtaining food resources. Within each strategy a number of
tactics may be employed to achieve the goal using that strategy. I have
already suggested that individuals using a hunting/gathering
strategy,
when confronted with food shortage, may employ one or more of four
tactics; movement, diversification,
storage, and reduction of rate of reproduction. What about a shift between strategies; what should be the
relationship between tactic and strategy shifts?
The concept of adaptive topographies (Stansfield 1977; Dobzhansky
74
RICHARD
W.
REDDING
19.51; Wright 1932) is applicable to this problem. One may think of hunting/gathering and food production as two peaks in a three dimensional
landscape of fitness values (there may be other peaks, but we are not
interested with them in this paper). Each peak has a number of crests or
ridges associated with it that represent the alternative tactics individuals
within a population might employ in pursuing the strategy. The valleys
separating these tactics are much less deep than the valleys separating the
strategy peaks. The landscape is continually shifting: the tactic that provides the highest fitness may change and the depth of the valleys between
peaks is contantly changing. Populations may occupy the slope associated
with each peak. Individuals
in the population may strive to attain the
peak, highest possible fitness value using that strategy, but probably rarely attain it because the landscape is not stable. For populations to shift
peaks, either the population must move directly from peak to peak or the
shape of the landscape must change. In the first case a major change in
human behavior is required; all the behaviors associated with a tactic or
strategy would have to appear at once to make it viable. Since the valleys
between tactics are much shallower (if they exist at all) than those between strategies, and the valleys between tactics probably change shape
and shift more rapidly than do the valleys between strategies, I would
expect tactic shifts to occur more frequently than would strategy shifts by
behavioral change. Indeed, tactic shifts may be part of the behavioral
repertoire of the population. But, due to the magnitude of the behavioral
changes needed to shift from, for example, hunting/gathering
and food
production
I would expect shifts between strategies
due to a
“macromutation”
in behavior to be unlikely. In this case, a change between strategies, will occur when one of the peaks is depressed so its
fitness value is below that of the intervening valley, when the fitness value
of the valley increases to form a bridge between the two peaks, or when
some combination of the two conditions exists. Again I would expect to
see shifts in tactics much more frequently than shifts in strategies. It is
possible that a shift between peaks could result from a combination of the
appearance of a new behavior and a change in the fitness landscape that
reduces resistance to peak shifts, but as an initial position I will assume
the priority of changes in the landscape.
Does an area of lower fitness, valley in the adaptive landscape, exist
between the peaks associated with hunting/gathering
and food production? Flannery (1972), has provided evidence that the shift to food production in the Near East was accompanied by a shift from the group as the
unit of production to the family as the unit of production. Such a shift
must have had profound effects on the hunter/gatherer societies making
the transition. Hesse (1982:2, 4-5), has elaborated on the importance of
these changes and their significance in relation to pastoralism. He con-
GENERAL
EXPLANATION
OF
SUBSISTENCE
75
CHANGE
eludes that because of the social conflicts involved in the shift: “. . .
transitional occupations are likely to be rare in the archaeological record
and pastoral management systems will seem to emerge suddenly from
hunting societies” (19825). Another point to be made is that in the early
phases of domestication
the cost/benefit ratios for domesticates are unlikely to exceed those for hunting or collecting the wild forms. Hence,
individuals engaging in early food production will have a lower fitness
than those utilizing hunting and gathering, unless the adaptive landscape
is altered.
Either a reduction in local carrying capacity due to an environmental
change, or a population that is at K and is stressing its resource base will
cause the fitness value of the peak to decrease and may cause the value
of the intervening valley to increase. Individuals in any population occupying a deteriorating peak will utilize all possible tactics to maintain the
highest fitness value possible. It is only when all tactics to maximize the
peak have been exhausted and the peak sinks below the level of the valley
separating the two strategies that movement to the second strategy will
become possible.
I will assume that an area of depressed fitness exists between hunting/
gathering and food production. Further, I will assume that tactic shifts,
within a strategy, are favored over shifts in strategy. Hence, all possible
tactical changes should occur before a strategy shift becomes a viable
option.
AN EXPLANATION
AND MODEL FOR THE ORIGIN
FOOD PRODUCTION
OF
The points made in the previous discussion form the base for the model
I have developed to explain the origin of food production. The model
hypothesizes the existence of four stages and four shifts in the continuum
from hunting/gathering
to food production. I want to emphasize that although the model is divided into stages the process is a continuum: these
stages are defined for convenience. Further, the process should not be
viewed as unilinear. A group may stop at any stage and may move back
and forth between stages.
In presenting the model I would like to begin with the initial populating
of any broad region of the world: it could be the Near East, Mesoamerica,
or Europe.
Stage I
In the frost stage a group of hunter/gatherers
enters the region but
initially utilizes only a small area of the region. Since the birth and death
76
RICHARD
W.
REDDING
rates, the components of r, are dependent upon environmental
parameters as well as the behavior of the individual, a period of adjustment will
ensue, but individuals in the population will not have adopted behaviors
to affect birth and mortality rates for the purpose of regulating their numbers since there has been no selective pressure to do so. After this period
of adjustment the population will increase at the rate permitted by the
local environment until the population approaches the carrying capacity
the area will support based on a simple hunting/gathering
strategy. At this
point selection should favor the adoption or use of behaviors that allow
individuals to put relatively more into reproduction. The tactic selection
should favor first is movement, i.e., emigration (Fig. 2). This is, in most
cases, the least expensive tactic and will be favored over a behavior that
involves individuals reducing reproduction for reasons stated earlier.
If a population using a tactic of mobility, encounters conditions that
allow individuals not engaging in mobility to have a fitness equal to or
greater than individuals using mobility, then mobility will have a negative
value and will be reduced in the behavioral repertoire of the group. Such
conditions could be encountered when a population moves into a new
area, or when environmental
fluctuations or changes in the demography
of the population affect the groups relation to the K for an area that is
allowed by simple hunting/gathering.
Local
carrying
capacrty
With
storage:
the
highest
~o~u,ation
pwmittm4
with
h”nti”g/gathe,ri”g
a
.3trll**gy
Local tarrying
Cap*city
vtilh *impI*
-
Ir”_
-
-
-
-i)b-
hunting/gathering
pop.
r*g.
m
stage I
FIG.
2. The
model:
stag. 111
stage II
shifts
from
Stage I through
Stage III.
_
_
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
77
Since any region is a mosaic of areas, providing a range of different
growth rates, some areas in a region will reach carrying capacity before
others. Variation in carrying capacity should be patterned; hence, large
sections, or clusters of areas, within a region will reach their carrying
capacity together. Eventually, because of rising population densities in
the clusters, the central areas, growth centers within the clusters, will be
unable to slough-off excess population. Areas peripheral to the growth
centers will have their own population problems. Growth centers will be
blocked from access to areas still capable of receiving emigrants by areas
that are at carrying capacity and may be sloughing-off their own excess
population, or emigration will be too expensive.
Stage ZZ
In areas of the highest growth rates in a region, when the population
approaches K and emigration is no longer possible, is too risky, or individuals using this tactic have a lower average fitness than individuals
using diversification,
then diversification of the resource base should be
favored (Fig. 2). Diversification
will raise the effective carrying capacity
of an area; allowing individuals using this tactic to put relatively more into
reproduction (producing more and/or better offspring). Diversification,
in
most cases, should be preferred over storage because of the lower cost. If
the area will not support diversification then the individuals should either
adopt a simple hunting/gathering
tactic or adopt behaviors that reduce
their rate of reproduction.
Limiting
reproduction will have a positive
selective value because by reducing the number of offspring an individual
can increase the probability,
relative to that of an individual in the same
population that does not limit his or her reproduction, that any offspring
raised will survive and that these offspring will be healthier.
Again, if a shift in demography or environmental
change results in an
increase in the K an area can support with either mobility or simple
hunting/gathering
to a level above the current population then individuals
engaging in mobility or simple hunting/gathering
should have an advantage over individuals using diversification.
Hence, one would expect to
see a shift in the behavior of the group.
Eventually, either: increasing the carrying capacity by increased diversification (use of more food resources) will not be possible; the cost/
benefit ratio will exceed unity; or, the cost/benefit ratio curve for diversitication will cross the cost/benefit curve for storage, and the local population will have reached the maximum carrying capacity of the area that
is permitted by using hunting/gathering
with diversification.
Stage ZZZ
Either one of two events can cause the development
of Stage III.
First,
78
RICHARD
W.
REDDING
continued growth, permitted by an increase in carrying capacity resulting
from the use of diversification,
will eventually result in a population that
is once again at or near K. Second, as mentioned above, the cost/benefit
curve for diversification
may cross the cost/benefit curve for storage.
Under either of these conditions selection should favor the adoption or
use of storage behaviors. The use of storage permits individuals using it to
put relatively more into reproduction.
Storage effectively increases the
carrying capacity by permitting full use of seasonally abundant resources.
In some areas seasonally abundant and storable food resources will be
absent and selection should favor individuals who limit their reproduction. Again, this is because of the advantage gained (relative to individuals
who continue to bear larger numbers of young) in total fitness by raising
fewer, higher quality young.
Once again if a shift in demography or environmental change results in
an increase in the K an area can support with diversification
to a level
above the current population then individuals engaging in diversification
should have an advantage over individuals using storage. Hence, one
would expect to see a shift in the behavior of the group.
Eventually, increasing the carrying capacity through increasing technology and increasing investment will no longer be possible and the local
population will have reached the limit that a hunting/gathering
strategy
can support in the area. At this point, as the population approaches K,
individuals using a hunting/gathering
strategy are occupying a receding
peak in the adaptive landscape and should utilize the final tactic available
to them, behaviors that limit an individual’s
reproduction,
to prevent
further decrease in the fitness value resulting from use of the strategy.
Under what conditions should individuals shift strategy?
Stage IV
Whether selection favors individuals who develop a new subsistence
strategy or individuals who utilize behaviors that reduce their rate of
reproduction will depend on the predictability,
frequency and severity of
fluctuations in annual yields in the area. For the purpose of further development of the model I will assume that environments may be divided
into two general classes: one in which fluctuations are more predictable,
less frequent, and less severe, and one in which fluctuations are less
predictable, more frequent, and more severe. In the subsequent discussion I think it will be apparent that it is frequency and severity of fluctuations that are critical to the model.
Under conditions of more predictable, less frequent, and less severe
fluctuations in annual yields, when a population has attained the maximum local carrying capacity a hunting/gathering
strategy permits, selec-
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
79
tion should favor individuals who utilize behaviors that reduce their rate
of reproduction (Fig. 3). Under these conditions carrying capacity is relatively more stable and the population may be close to carrying capacity
at all times. The absence of short-term fluctuations that produce a superabundance of resources means that a tactic of limiting reproduction has a
higher total fitness value than a tactic of continued reproduction. With
limited resources, individuals who limit reproduction will produce offspring with a higher probability of survival and of higher quality than
individuals who do not limit their reproduction. Limiting reproduction
will keep the hunting/gathering peak in the adaptive landscape from sinking below the adjoining valley; hence, the opportunity to shift to another
strategy, food production, never obtains. The absence of short-term, severe depressions in resources, or resource failure, eliminates any potential advantage that might accrue to an individual that invests labor in
planting/rearing and defending wild occurring resources.
Under conditions of less predictable, more frequent, and more severe
fluctuations, when a population has maximized the local carrying capacity
using a hunting/gathering strategy, selection should not favor individuals
who attempt to reduce their rate of reproduction. Under these conditions
behaviors limiting reproduction would have to keep the general population at such a low level that during fluctuations resulting in periods of
sustained high yields the behaviors should break down. Further, due to
the unpredictable, severe nature of the variations in annual yield, it would
be difficult for the behaviors affecting birth and mortality rates to track
them. Under conditions of unpredictable, more frequent, and more severe
stage
FIG.
3. The
model:
III
shit
stage
from
Stage
IV
III to IV.
80
RICHARD
W.
REDDING
fluctuations behaviors that limit an individual’s
reproduction would not
have a positive selective value; hence, the hunting/gathering
peak would
slowly sink-its
fitness value would continue to decline as increasing
population stressed local food resources during unpredictable,
severe declines in the food resources. As the fitness of the hunting/gathering
peak
declines another factor would come into play that facillated the shift to
food production.
Under conditions of a declining peak for hunting/
gathering, individuals who maintain small patches of wild plants or small
groups of wild animals as insurance or a back-up would have a selective
advantage over individuals relying only on naturally occurring wild resources. This will result in a rise in the fitness value of the valley between
hunting/gathering
and food production. Without population pressure and
unpredicable, severe depressions in the subsistence base, individuals that
invest labor in planting a wild resource or caring for captured animals
would be wasting their time; there would be no selective advantage to
planting and herding. Eventually the adaptive peak associated with hunting/gathering will have a fitness value less than that of the valley separating the peaks of hunting/gathering
and food production, and behaviors
associated with food production should spread in the population.
In the early phase of domestication yields from the plants and animals
need not be any higher than yields obtainable from the same resources in
the wild. This is true because yields at this point are supplemental: they
provide insurance against unpredictable, severe depressions in local food
resources. The function of food production at this point is not to replace
hunting/gathering
but to provide a back-up to collected food resources.
Since the yields from the manipulated plants and animals in this early
phase are supplemental they should form only a minor part of the total
food resources consumed. Once planting crops and caring for herds has a
positive contribution to an individual’s total fitness, then manipulating the
genetic structure of the potential domesticates in order to increase yield
per unit of labor, should have a high positive selective value. At some
point a combination
of reliability and return per unit of labor for the
incipient domesticates exceeds the reliability and return for first choice
hunted/gathered
resources, and settlements based predominantly
on domesticates should appear; the population should begin to climb towards
the peak associated with food production.
SOME
GENERAL
COMMENTS
ON THE MODEL
I would like to discuss six points not explicit in the discussion of the
model but which are important to a complete understanding of the explanation I am proposing.
(1) In this explanation the function of food production behavior in its
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
81
initial stage is to provide insurance against a short fall or failure in one or
more segments of the resource base. Initially, food production was not an
alternative to hunting and gathering. Indeed, early food production behaviors may have been employed at the start of a year and then abandoned before harvest when it became apparent that wild resources were
abundant enough that year. This bridging function for food production
behaviors would not require all of the social changes of full involvement
in food production; and the existence of such a bridging function may
have raised the fitness value of the valley between hunting/gathering
and
food production. However, the bridging function would only come into
play when the population was under resource stress in environments with
less predictable, more frequent, and more severe fluctuations in the food
resources.
In a recent study of the effect of the origin of food production on the
human diet, Schoeninger (1981) has demonstrated that no major change in
subsistence accompanied the origin of food production. She argues that
the origin of food production is associated with a change in the economy,
“ . . . a change in the management of previously developed subsistence
systems” (Schoeninger 1981:87). This is congruent with the bridging function proposed above for the early phase of food production.
(2) I have tried to stress the importance of population growth in an
area as a factor conducive to the origin of food production. I see a high
carrying capacity as much less important. Note that a high growth rate
and a high carrying capacity are not necessarily associated. An area may
support a high growth rate and have a high carrying capacity but I would
expect most such areas to have more predictable, less frequent, and less
severe fluctuations in annual yield. Hence, individuals in such areas
should evolve behaviors that result in more stable populations rather than
shift subsistence strategy to food production. Examples of this type of
area-high
growth rate, high carrying capacity, and stable environmentmay be found along coasts.
(3) The selective milieu seen as crucial in this explanation to the
development of food production is the result of the cooccurrence in an
area of populations that: have utilized all tactics that are available to them
with a hunting/gathering
subsistence strategy, except limiting population;
are at or near K; and, are in an environment in which fluctuations in food
resources are less predictable, more frequent, and more severe. Each of
these factors may operate independently but it is only when they all occur
at once that food production should emerge. Fluctuating environments
have always exerted selective pressures on human subsistence but up to
the point of strategy shift stresses caused by fluctuations in the resource
base may have been handled by tactic shifts. Indeed, as suggested earlier,
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RICHARD
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fluctuating environments may have been the cause for the inclusion of
different tactics in the hunter/gatherer behavioral repertoire.
(4) Other selective pressures may have been operating in any particular area to favor the adoption of food production but they are not necessary to the explanation. Two examples are sedentism and long term
environmental fluctuations. The explanation makes no assumptions about
the appearance of sedentism. Sedentism would certainly allow for increased population growth by permitting closer spacing of births; hence,
sedentism would be an additional source of selective pressure on subsistence behavior. Sedentism in this model is not a prerequisite of food
production, but would intensify the selective pressure for it. How effective sedentism was as a contributing factor in an area may have depended
on the species that were the focus of early food production. For example,
in areas in which wheat and barley were the primary species utilized
sedentism was probably more important a force than in areas that relied
heavily on sheep and goats. Long term environmental
fluctuations (e.g.,
the environment becoming increasingly dry) may lower the K for an area
under any subsistence tactic or strategy, resulting in population pressure,
but this in itself is not sufficient cause for a shift in subsistence strategy.
However, it may have been in some areas at some times a contributing
factor.
(5) As I have tried to emphasize throughout this paper I do not intend
to imply in the explanation that there exists a unilineal, irreversible sequence from movement to diversification
to storage to either food production or a stable population. Some areas may not have been capable of
supporting any diversification
and developed a stable population. Environmental change, disease, or some catastrophic agent may disrupt population growth causing a group to go from, for example, using storage to
diversification.
(6) This model makes no statements on the relationship between the
appearance of domestic plants and domestic animals. This is an interesting problem that probably goes beyond simple availability. It may best be
tackled by examining availability,
risk, and local nutrition as part of an
optimization
model.
The explanation of the origin of food production presented above owes
much to previously published works but differs from them significantly.
All other explanations I have encountered either ignore the problem of the
evolution of individual behaviors that limit reproduction, or assume they
always operate to stabilize human populations and to understand subsistence change we must determine what conditions might make these behaviors ineffective. The explanation provided here specifies under what
conditions individuals should engage in limiting their reproduction and
under what conditions these behaviors will fail.
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
83
The explanation presented here relies on an interaction of population
growth and fluctuations in food resources, presumably primarily related
to fluctuations in environmental
variables. Only two other published explanations have considered the role of oscillating environments (Hassan
1977, 1981; Hesse 1982). Hesse’s explanation is limited to animal domestication and fails to explain why domestication appeared when it did and
why domestication did not occur in other areas. Hassan’s explanation is
intended to explain the origin of food production in the Near East, but it
offers a testable explanation of why it did or did not occur in other areas.
However, it differs from the one provided here in a number of ways.
First, Hassan assumes that a demographic study of living and prehistoric
human groups indicates that prehistoric populations used regulatory behavioral mechanisms to maintain their population below carrying capacity. Second, Hassan considers that changes in the environment at the end
of the Pleistocene, an environment that had been susceptible to major and
frequent climatic fluctuations, increased the seasonal and spatial predictability of the resource base in the Near East. This led to the broad spectrum revolution and, eventually, the domestication of cereals. I maintain
that environments with less predictable, more severe, and more frequent
fluctuations provide an important part of the selective milieu. General
environmental trends could provide an additional source of selective pressure, but a general increase in predictability
and stability, as proposed by
Hassan, should retard the development of food production. Finally, HasSan’s explanation requires sedentism.
In a recent short review of the origins of food production Binford (1983)
touched upon many of the points central to the explanation presented
here. He suggests that more consideration should be given to Darwinian
arguments (Binford 1983:203). He notes that selection for change must
occur when available tactics fail due to changed environmental
condition
(Binford 1983:203).
SOME GENERAL
PREDICTIONS
This explanation has a number of implications
that can be tested with
archaeological data. While I do not intend to do an exhaustive review of
the data in terms of the test implications 1 would like to briefly discuss six
of them.
(1) One of the strongest features of the explanation provided here is
that it specifies, at least in a comparative fashion, those areas within a
region in which food production would be favored. Areas in which food
production developed should exhibit relatively less predictable, more frequent, and more severe fluctuations in food resources. While the appli-
84
RICHARD
W.
REDDING
cation of measures of predictability,
frequency, and severity in fluctuations of food resources to areas in which food production never developed, yet which had high population densities (e.g., northwest coast of
North America), should show that such areas had predictable, infrequent,
mild fluctuations (please note that I am not suggesting that these areas
were not subject to fluctuations, but that they were relatively more predictable, less frequent, and less severe). Further, areas that never attained food production, prior to colonization by groups using intensive
agricultural practices, should be occupied by groups involved in either
diversification
or storage and show low rates of population growth or
individuals in the population should use behaviors that limit their reproduction.
A problem that must be overcome to utilize this test is the development
of measures of predictability,
frequency and severity of fluctuations in
resources. If we assume that variation in rainfall is a good predictor of
interannual variation in yields and that the rainfall patterns in a broad
region (e.g., the Near East) at the time of the origin of food production are
similar to what they are at present, then modem rainfall data could be
utilized to rank areas within a region as to predictability,
frequency, and
severity of fluctuations. The earliest evidence of food production should
be found at sites in areas with less predictable, more frequent, and more
severe fluctuations in rainfall. Measures adapted by ecologists (Colwell
1974) may be applied to rainfall data from different areas to test for differences in their fluctuations. Unfortunately,
I have run into two problems with using rainfall data in the Near East. First, long-term data on
rainfall is available for very few locations in the Near East, and only one
station is located near a site that contains evidence of early food production. Second, rainfall is a very poor predictor of annual variation in local
food resources for areas that have aquatic resources, i.e., swamps, areas
near lakes, and coastal areas. At present I am attempting to develop
variables that can be used to establish measures of predictability,
constancy, and contingency for archaeological sites. It should be possible to
use the fauna1 and floral data from sites along with data on local paleoenvironments to construct the needed measures. These then may be used to
compare the nature of fluctuation between areas. Another possible source
of data on interannual variations in yield might be tree rings. A comparison of ring data between sites and areas may allow us to establish relative
predictability,
frequency, and severity of fluctuations of resources.
(2) The explanation requires that populations in areas with the earliest evidence of food production be increasing such that they are continually approaching K and expanding the K of the local environment by
adopting a succession of subsistence tactics and, ultimately,
strategies.
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
85
Hence, we should find evidence of population pressure. Population pressure is difficult to demonstrate because operationalizing
the concept of
carrying capacity has proven to be fruitless (see the discussion on carrying capacity). The substitution of relative densities as an estimate of population pressure is also a mistake, for, as discussed above, high density
and population pressure are not necessarily linked. The simplest way to
test the explanation is to examine changes in the size of the population in
the same area over time. The explanation requires that the population
increase in an area that exhibits long term, sustained, shifts in subsistence
tactics and strategies.
(3) The explanation also requires that a sequence of shifts in tactics
occur with the population using a strategy of hunting and gathering before
a shift to a strategy of food production obtains.
(4) A prediction related to the shift from diversification to storage is
that after evidence of storage technology appears no further diversification will obtain. The indices of diversity and niche breadth will be at their
maximum just prior to the appearance of evidence of storage technology.
(5) Another consequence of the explanation, which has already been
mentioned, is that the contribution
of domesticates initially should be
small, since at first the function of food production is as a back-up food
source. It is only after either, the early domesticates exhibit morphological or behavioral changes, or, the humans exhibit behavioral changes that
result in a greater efficiency of production from the early domesticates
that domestic plants and animals should replace wild resources. At this
point the function of behavior related to food production shifts from insurance to a primary food source.
(6) As stated previously, I do not believe that the burials from a
population at or near K should necessarily exhibit evidence of increased
mortality and morbidity. In a population at or near K a general increase in
morbidity and mortality should occur only with unusually severe fluctuations in the resource base. The effect of these types of events on the data
offered by burials should be minimal. If being at or near K has any long
term effect on the population we should see it in an increase in infant
mortality and a shift in the age curve reflecting a lower birth rate. However, as suggested in the explanation these effects should be transitory
because selection will favor individuals that develop or utilize tactics and
strategies that allow them to put relatively more into reproduction.
THE EXPLANATION
IN THE CONTEXT
ARCHAEOLOGICAL
DATA
Although
OF SOME
I am not prepared at this point to offer a formal test of the
86
RICHARD
W.
REDDING
explanation, I would like to briefly examine it in the context of some
archaeological data. This exercise will illustrate the utility of the explanation and some additional ways by which the explanation can be tested.
The Broad Spectrum Revolution
The diversification
of the food base and its importance in the development of food production has received increasing attention (Flannery 1968;
Cohen 1977b; Christenson 1980; Earle 1980; Hesse 1982). A diversification in the resource base has been documented in California (Jefferson
1971), the midwestern United States (Christenson 1980), the Tehuacan
Valley (Christenson 1980), Paleolithic Spain (Straus 1977), the Near East
(Flannery 1973), and Egypt (Clark 1971; Wendorf and Schild 1980a). Interestingly, this diversification is not always associated with the development of food production.
It is, however, associated with population
growth (Cohen 1977b). Christenson (1980:34-38), has provided a model of
diversification
and its relation to population density and applied it to
archaeological data sets from two regions: the Tehuacan Valley and the
midwestern United States. Christenson suggests that diversity should increase with increasing population density (population pressure). His calculation of resource diversity and niche width for the two areas, when
cross plotted, exhibit a steady increase to a point at which resource diversity continues to increase, but niche width begins to decrease. Of
interest in this discussion is the fact that in both areas Christenson found
that food production arose when the niche width was maximized. This
indicates that utilization of food resources was evenly and widely spread;
wild food resources were probably being utilized at maximum efficiency.
The subsequent increase in the index of diversification
and decrease in
niche width reflects the use of both wild and domestic resources with
increasing dependence on domestic resources. Christenson’s
model
makes an excellent submodel for the diversification stage of the explanation presented here. All of his findings are consistent with the explanation
presented here, in fact, as indicated above, the shapes of his curves and
the position of the origin of food production on those curves support the
explanation.
Diversljkation
in Wadi Kubbaniya4
We may have an example of environmental
change causing a
“reversal” in the expected sequence of tactics in the Late Paleolithic of
Egypt. Work in Wadi Kubbaniya (Wendorf et al. 1979; Wendorf and
Schild 1980a) was thought to provide evidence of intensive use, and possibly domestication of barley at 18,000 to 17,000 B.P. Recent work (Wen-
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
87
dorf and Schild 1984; Wendorf et al. 1984) indicates that barley was not
present at that date in Wadi Kubbaniya, but it appears that the inhabitants
were utilizing a number of edible plant species. The data seem to indicate
that the inhabitants were utilizing the tactic of diversification.
The use of
plants seems to have ceased or decreased dramatically by 12,000 years
ago (Wendorf and Schild 198Ob:278). When it was believed that evidence
for the early use of barley (perhaps domestic) was present at Wadi Kubbaniya two explanations
were offered for its disappearance.
Hassan
(1979) suggested that series of catastrophic Nile floods made it impossible
to plant crops and after the floods the area was either altered so that it
could no longer support cultivation or the people “forgot” how to cultivate barley. Wendorf and Schild (198Ob:279), suggested that the microhabitat that favored grain cultivation disappeared when the Nile level
dropped around 12,000 years ago. I would like to offer an alternative
explanation, based on the model I have presented here, for what now
must be seen, at best, as a retreat from diversification.
From 19,000 to
17,000 years ago the desert around Wadi Kubbaniya was hyper-arid
(Wendorf et al. 1977). Because of the deteriorating
conditions on the
desert we might expect groups to have migrated into the Nile valley or to
have concentrated more of their subsistence activities there as the Nile
valley provided the ‘ ‘ . . . only available moisture” (Wendorf and Schild
1980b:276). This might have created a population that exceeded the carrying capacity of the area. Hence, selection would have favored diversification and, perhaps, storage. When evidence of diversification
disappeared about 12,000 years ago, “. . . the conditions of hyper-aridity were
being replaced by increasing monsoonal rainfall, marking the onset of the
Holocene wet period”
(Wendorf and Schild 198Ob:279). The desert
opened up and emigration became a viable tactic again for relieving population stress. Since emigration is less expensive than diversification and
storage, the Wadi Kubbaniya population(s) ceased utilizing more expensive foods and shifted to emigration to avoid stress on the subsistence
base. Of interest in regard to this explanation for the pattern at Wadi
Kubbaniya is the decline in the number of sites along the Nile at about
12,000 years ago (Wendorf and Schild 198Ob:278), presumably associated
with a decrease in population density.
Near Eastern Archaeological
A Selective Review
Data on the Origin of Food Production:
Our best body of data on the evolution of human subsistence, after the
appearance of hunting and gathering, comes from the Near East. The
following is a very selective, noncomprehensive
review of the archaeological data for the Near East and is undertaken only to illustrate the
88
RICHARD
W.
REDDING
congruence of the model with the data base and to indicate additional
ways in which the model might be tested against the Near Eastern data
set.
The fauna1 and floral data derived from the Upper and Epipaleolithic
sites in the Near East indicate that some time prior to 22,000 years ago a
trend toward diversification
of the subsistence base began (Flannery
1969:77; Redman 197857-87). Populations in the area that began diversification entered Stage II of the model. As suggested in a previous section, as part of the diversification process we should see an increase over
time in use of second and third choice foods: the indices of diversity and
niche breadth should both increase. It should be possible to estimate the
costs and benefits of each of the potential resources in the Near East.
Using these data we should be able to predict the order for the addition of
resources. Predictions based on this ordering may then be tested with
archaeological data from the area.
Starting around 11,000 years ago subterranean pits appear in some sites
in the Near East. Pits have been reported from a number of sites including
Zawi Chemi Shanidar (Solecki 1964), Karim Shahir (Braidwood and
Howe 1960), Mureybit (Van Loon et al. 1968). ‘Ain Mallaha (Perrot 1966),
and Hayonim Terrace (Henry 1981). Whether these pits were used for
roasting or for direct storage they represent an investment in storage.
Populations investing in storage are in Stage III of the model. The model
predicts that evidence of storage technology should appear in the archaeological record prior to the development of food production and this is the
case in the Near East.
Although diversification and even storage may have been utilized over
a broad area or even over an entire region, based on the explanation
offered here the areas of a region in which we should have evidence of the
greatest diversification,
the earliest storage and the earliest evidence of
food production should be those areas that had the highest population
growth rates; and, hence, were the areas that put the most stress on their
food base. Given the discussion in the section on human population
growth, ecotonal areas probably had the highest growth rates and are the
most likely sites for the chain of events described in the explanation. In
the Levant the Epipaleolithic
and Early Neolithic sequence is: Early Kebaran, Late Kebaran, Geometric Kebaran, Early Natufian, Late Natufian, pre-pottery Neolithic A and pre-pottery Neolithic B. Although diversification appears in Kebaran sites in the Levant, it is the Natufian
sites in which diversification is maximized and storage structures appear.
Interestingly,
Natufian sites are limited to ecotones (Henry 1981:427). It
is in these same areas in PPNA (pre-pottery Neolithic A) sites that the
earliest evidence of food production appears. Hence, in the Levant, maximum diversification,
storage and food production appear in the ecotonal
GENERAL
EXPLANATION
OF
SUBSISTENCE
CHANGE
89
areas in which population, based on occupation area, expands at a much
faster rate.
One of the implications
of the model is that domestic forms initially
contributed in only a minor way to the diet; they functioned as insurance
against periods of resource shortage. The two early food producing sites
in the Near East for which we have the best data on flora and fauna are
Ali Kosh (Hole et al. 1969) and Cayonii (Braidwood et al. 1971, 1974). At
Ali Kosh use of domestic plants increased slowly; with domestic seeds
going from 5% of the seed count at about 7000 B.C. to about 40% by 6000
B.C. (Hole et al. 1969:367). Redman (1978:155) provides a graphic representation of the slow increase of domestic plants and animals in the food
base at Cay&ii.
The model requires that food production arose in areas in which fluctuations in the food base were less predictable, more frequent and more
severe and in which the population was growing. I have discussed above
the difficulties with estimating predictability,
frequency and severity of
fluctuations in the resource base. At present we have no estimates or
measures of these variables for the Near East. The question of whether
the population was increasing in the areas of the Near East in which the
documented shifts in tactic and strategy occurred is somewhat easier to
approach. Recent summaries of work in the Levant indicate that population was increasing continually from diversification through food production (Bar-Yosef 1975; Henry 1981; Smith et al. 1984). Interestingly,
during
the late stages of the Natufian in the Levant, just prior to the appearance
of food production in the area, Natufian groups expanded into the marginal areas displacing indigenous groups which had continued the Geometric Kebaran tradition (Henry 1981:429).
CONCLUSION
Optimal foraging theory has been extensively employed by ecologists in
explaining patterns and changes in subsistence behavior (for a review see
Pyke 1984). Anthropologists
have used this approach to examine subsistence behavior in hunter/gatherers (e.g., Winterhalder
and Smith 1981)
and in food producers (Hastorf 1980; Redding 198 1; Johnson and Behrens
1982; Keegan 1986). In order to construct an optimal foraging model for
subsistence behavior the goal of the subsistence behavior must be established. Most evolutionary ecologists and anthropologists
have assumed
that the goal of subsistence behavior is energy or some function of energy
return per unit of expenditure. They have made this assumption in order
to test whether the species was behaving in an optimal fashion. In a study
of pastoralism in the Near East I utilized a different approach: I assumed
90
RICHARD
W.
REDDING
that humans behave in an optimal fashion and tested a series of goals. The
goal that the pastoralists seemed to be using was security (Redding 1981).
Widstrand (1975:149) has stated that the goal of humans in herding animals is not the production of a marketable surplus, but the continued
provision of a food supply to enable the herding group to survive physically and socially, and the maximization
of the probability that the group
would survive “. . . prolonged droughts and other risks.” Pyke et al.
(1977: 140), in reviewing the application of optimal foraging theory to nonhuman predators, suggest that if an animal can retain exclusive use of an
area then the animal could manage the resources of the area for sustained
yield. In a long-lived species in which the juveniles are dependent upon
the parents for an extended period security of the resource base must be
an extremely important consideration.
The explanation I have presented is preliminary
in nature; it is an
explanation sketch. It, however, reflects my belief that the underlying
selective pressure shaping human subsistence behavior is resource security. The decisions made by individuals at each stage of the model reflect
attempts to avoid resource uncertainty. The explanation and model would
have been significantly different if I had assumed that humans were acting
in a fashion as if they were maximizing energy or some nutrient yield.
A major goal of anthropologists and archaeologists is the explanation of
changes in human technology, settlement patterns, and economic and
social organization.
Because of the strong interaction and relationship
between the evolution of subsistence systems and cultural systems, if
anthropologists
and archaeologists are to attain their goal they must be
able to explain the documented changes and variation in human subsistence behavior. The explanation for the evolution of human subsistence
from hunting/gathering
to food production I have presented here is an
initial step in this program.
ACKNOWLEDGMENTS
I have greatly benefited from discussions with a number of people. In particular I thank
Phil Myers for pointing out to me the work of S. Wright on adaptive landscapes. Cheri
Alexander, my wife, edited the final draft and provided moral support throughout the writing
process. Henry Wright, Phil Myers, Kate Moore, and Patti Wattenmaker all read various
drafts of the paper and aided me with their comments. Two anonymous reviewers offered
valuable criticism for which I thank them very much. However, as always, any errors,
omissions, or faults in logic are the author’s alone.
NOTES
’ One can undertake the analysis of the selective pressures favoring the development of
a mutuahsm from the point of view of the plant/animal or the human: they are undoubtedly
GENERAL
EXPLANATION
OF SUBSISTENCE
CHANGE
91
different. However, for the multualism to develop it must increase the fitness of both
symbionts.
’ However, one must always take into consideration the possibilities that the pressures
were operating but an alternative variant arose fast and was fixed in the population by some
cultural means, or the variant “food production,” or the variant leading to it, never arose.
3 One reviewer pointed out that an awareness of planting seeds etc. does not make one a
farmer. But I am not arguing that they could be farmers, merely that their knowledge
permitted use of a behavior that was not farming but which gave them a selective advantage
over individuals using a hunting/gathering strategy.
4 The Wadi Kubbaniya data presents a number of problems. At least one reviewer and two
other colleagues suggested that I avoid that data set. I present the discussion of it here only
to illustrate some of the ideas developed in this paper.
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