Download Hunter-Gatherer Foraging Strategies in Tropical Grasslands: Model

JOURNAL OF ANTHROPOLOGICAL ARCHAEOLOGY
ARTICLE NO.
16, 189 – 225 (1997)
AA970309
Hunter–Gatherer Foraging Strategies in Tropical Grasslands:
Model Building and Testing in the East African
Middle and Later Stone Age
Curtis W. Marean
Department of Anthropology, SUNY at Stony Brook, Stony Brook, New York 11794-4364
Received October 30, 1996; revision received February 24, 1997; accepted May 1, 1997
Hunter–gatherer adaptations to moist tropical grasslands are not well known from either the ethnographic or the archaeological record. This is unfortunate as grassland adaptations are clearly significant
to human biological and behavioral evolution. The most effective strategy for remedying this problem is
to develop models for grassland exploitation based on strong understandings of the ecological similarities
and differences between cold, temperate, and tropical grasslands. Cold, temperate, and tropical grasslands
are similar in that water and raw materials are often scarce and the most abundant large mammals are
gregarious and mobile. Tropical grasslands differ from cold and temperate grasslands by having a greater
diversity and biomass of edible above-ground plants and plants with underground storage organs, making
carbohydrate availability greater and less seasonal. Large mobile mammals and resident large mammals
are more diverse and have greater biomass in tropical grasslands. Overall, tropical grasslands are a richer
and less seasonally punctuated environment than either cold or temperate grasslands. A comparison of
ethnographic data regarding variation in foraging strategies in different cold, temperate, and tropical
settings lead to the construction of three models for hunter–gatherer exploitation of tropical grasslands: a
Generalized Grassland Model (no specialized tactical hunting—considered the favored model given modern African grassland conditions), a Seasonal Grassland Model (only seasonal use of specialized tactical
hunting techniques—considered unlikely for Africa), and a Specialized Grassland Model (regular use of
specialized tactical hunting strategies—considered highly unlikely for Africa). A preliminary test of these
models shows the Athi-Kapiti Plains Holocene archaeological evidence is most consistent with the Generalized Grassland Model. The Last Glacial Maximum is most consistent with the Seasonal Grassland Model.
A single MSA occupation also suggests that specialized tactical hunting strategies were used. These
differences in hunting strategies were probably due to the differences in ecological conditions between the
Holocene and the Last Glacial Maximum. q 1997 Academic Press
Wissler (1927: 22 – 23) wrote that ‘‘all
Plains tribes seem to have practiced cooperative hunting in an organized military-like
manner.’’ By ‘‘military-like’’ Wissler is referring to the communally organized hunting
that often used natural or modified features
of the landscape to tactical advantage. The
Eskimo practiced similarly complicated
hunting maneuvers, and both Plains Indians
and Eskimo aimed these military-like tactics
against large gregarious mobile species, the
bison and the caribou, respectively. Tropical
grasslands in Africa team with large mobile
prey that often pack closely into huge herds.
Not one observation exists, however, of African hunter – gatherers in grasslands using
the military-like hunting techniques described above for Plains Indians and the Eskimo. Why is this? Addressing this question
is essential for understanding hunter – gatherer adaptations to tropical grasslands, and
understanding human evolution overall.
The idea that tropical African grasslands
were specially significant to human evolution has been with us a long time. Dart (1925)
thought that life on the grasslands provided
the selection pressures that shaped the human intellect. Many models of human evo-
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CURTIS W. MAREAN
lution identify grasslands as a likely ecological context for the development of bipedal
locomotion and other physiological, anatomical, and behavioral characteristics of
hominids (Isbell and Young 1996; Lovejoy
1981; McHenry 1982; Wheeler 1984, 1991,
1992). Grasslands figure prominently in
most hominid foraging models (Blumenschine 1987; Bunn and Ezzo 1993; Foley
1987; Potts 1988; Rose and Marshall 1996). It
is likely that African grasslands will play an
important role in the debate over the origins
of modern humans, as the variants of the
Replacement Model argue for an origin in
Africa sometime between oxygen isotope
stages 8 and 6 (Aiello 1993). Though the paleoenvironmental data for this time are poor
in Africa, data from the more recent Late
Quaternary show a tendency for most of Africa to be colder and drier during glacial periods with a consequent expansion of grasslands (Deacon and Lancaster 1988; Hamilton
1982). Thus, grasslands were likely to have
been abundant during isotope stages 8 and
6 when modern humans were evolving.
From a distance grasslands seem similar;
expansive landscapes of swaying grasses
and slowly migrating ungulates. In reality
there is great variability within grassland
ecosystems and between grassland ecosystems, particularly in the availability of those
items most significant to humans: water,
plant foods, animal foods, and raw materials. I use the term ‘‘grassland’’ to refer to
any herb-dominated vegetation community
(De Vos 1969) — typically grasses but also
including sedges. One similarity that crosscuts all grasslands is the dominance of the
faunal biomass by large mammals (Coupland 1993: 479), those typically in the size
range (above 5 kg) preferred by hunter –
gatherers. Second, most of these large mammals are gregarious and mobile grazing species of ungulates. This similarity combined
with the well-known ethnographic record
for Great Plains Indians has structured most
of our ideas about grassland hunter – gath-
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erer existence. The diversity and density of
these mobile mammals is highly variable,
however, and tropical grasslands typically
have an abundance of non-mobile large
mammals that may be important sources of
food. Equally significant, grasslands in different climatic zones vary in the density and
availability of plant foods edible by people,
as will be discussed below.
Despite the recognized significance of
grasslands, it is humbling to realize that we
know very little about hunter – gatherer adaptations to tropical grasslands, though we
know more about hunter – gatherers in cold
grasslands and temperate grasslands. As defined here, cold grasslands occur roughly at
60 degrees latitude and above. These environments are often dominated by sedges or
grasses with significant lichen and moss representation and the large mammal communities are dominated by migratory caribou
(Pielou 1994). The two cold grassland ecosystems discussed here include the Barren
Grounds steppe on the north-west coast of
the Hudson Bay and the arctic prairie and
tundra along the flanks of the Brooks Range
in north-east Alaska. Temperate grasslands
occur between 60 degrees latitude and the
tropics, and my primary focus will be on
the various grassland ecosystems within the
North American Great Plains and Great Basin. Tropical grasslands occur between the
tropical latitudes, and in Africa there are
many grassland ecosystems of great diversity. While all three grassland types experience dramatic seasonal fluctuations in rainfall, only temperate and cold grasslands are
subject to significant seasonal fluctuations in
mean daily temperature (Ripley 1992). I will
argue below that tropical grasslands differ
from cold and temperate grasslands in ways
that make adaptations to cold and temperate
grasslands poor direct analogs for tropical
grasslands. This tripartite classification,
however, is not rigid but serves as a useful
simplification.
Most of the ethnographic data on tropical
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TROPICAL GRASSLAND HUNTER – GATHERERS
hunter – gatherers derives from either forest
hunter – gatherers or arid grassland hunter –
gatherers, such as the various San groups
and the Hadza. Forest hunter – gatherers are
unarguably poor analogs for grassland
hunter – gatherer subsistence due to the critical differences in forest and grassland flora
and fauna. Arid grassland hunter – gatherers
live in environments that are on the edge
of grassland classification (areas that receive
below 500 mm of rainfall; Lind and Morrison 1974; Pratt and Gwynne 1977). This
leaves a gap between 500 mm and about
1500 mm that remains poorly documented
ethnographically. It is in this gap that conditions exist for creating the classic moist
tropical grassland ecosystems where large
ungulates are diverse and dense and move
long distances in large groups. This lack
of data was recognized some time ago by
Foley (1982).
Thus, hunter – gatherer adaptations to
moist tropical plains ecosystems of the kind
represented by the Serengeti in Tanzania or
Athi-Kapiti plains in Kenya remain an
enigma. This is largely because hunter –
gatherers were displaced or absorbed by
pastoralists from these excellent rangelands
long before the hunter – gatherers were ethnographically observed. The earliest sheep/
goat remains in East Africa occur in northern
Kenya (Owen et al. 1982) and central Kenya
(Marean 1992a) before 4000 BP. At this time
East Africa was just entering a dry phase
that resulted in an expansion of grassland
and a decrease in woodland (Hamilton
1982). The prior early Holocene wet phase
may have presented vegetative conditions
that excluded pastoralism (Bower 1991;
Marean 1990). These initial thrusts by pastoralists probably involved substantial burning to open the plains to grass and to drive
back the tsetse fly, a pattern well documented among modern East African pastoralists. The middle Holocene dry phase, and
the consequent expansion of pastoralists,
combined to produce essentially modern
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East African grassland ecosystems (Marean
1992a, 1992b). The big losers were hunter –
gatherers who could not compete against
the more militant and organized pastoralists. The result was that by the time systematic ethnographic observations were
made, people practicing a hunter – gatherer
existence were absent from the moist grasslands.
This is both frustrating and stimulating. It
is frustrating because archaeologists usually
work from the present to the past when explaining the archaeological record, and
clearly this is not possible as regards
hunter – gatherers in tropical grasslands.
However, the problem is stimulating because it leaves archaeology as practically the
only viable means of investigating the tropical grassland adaptation of hunter – gatherers. The question, of course, is how do we
build an understanding of adaptations to
tropical grasslands on the basis of archaeological evidence alone?
I believe the proper procedure is to construct a comparative understanding of cold,
temperate, and tropical grassland ecology.
First, we need to define the relevant ecological parameters in tropical, temperate, and
cold grasslands that structure human foraging adaptations. Second, we must examine
the differences and similarities in ecology
among the three grassland types. Third, we
should look for structural correlates between ecological parameters and human behavior in the ethnographically known cold
and temperate grasslands. Fourth, we need
to build models of foraging strategies for
tropical grasslands based on points one
through three above, and guide these models with behavioral ecological theory. Fifth,
we can test those models with archaeological data.
This paper will concentrate on the first
four steps outlined above and finally apply
some preliminary archaeological data from
the Athi-Kapiti Plains to the developed
models. Hunting strategies are part of an
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CURTIS W. MAREAN
overall foraging strategy that includes a dynamic relationship between decision-making for plant-food collection and hunting,
but the archaeological data available at this
stage are restricted to zooarchaeological remains. My approach is guided by the basic
tenets of behavioral ecology, but much of
what I will discuss will be framed qualitatively as the quantitative information typically used by behavioral ecologists is lacking
or inaccessible in the archaeological record.
GRASSLANDS AND HUMAN
SUBSISTENCE
The most important ecological parameters
to compare are those most closely tied to
human foraging needs; they include diversity, biomass, seasonal availability, and predictability of plant and animal foods. Foley
(1982) attempted to estimate these parameters for the purpose of building a model of
human exploitation of tropical environments. Foley argued that hunter – gatherers
in xerophytic plant communities (those below 500 mm of rainfall per year) should receive most of their calories from plant foods,
particularly plants with underground storage organs (USOs). Drawing upon some
basic ecological principles and the data
available at the time, Foley argued that
‘‘woodland and forest hunter – gatherer
populations, such as the Mbuti Pygmies,
will subsist primarily on plant foods, as in
the higher rainfall regimes these are more
abundant’’ (Foley 1982: 398). Ethnographic
and ecological data on forest hunter – gatherers has increased in quality and quantity
since Foley’s paper, and the new data disprove the forest predictions of Foley’s model
by documenting a scarcity of plant foods
(Bailey et al. 1989; Bailey and Headland
1991; Hart and Hart 1986; Headland and
Reid 1989). Foley hypothesized that tropical
grasslands receiving between 500 and 1500
mm of rainfall would have few plant species
edible by humans and that hunter – gather-
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ers in these environments would rely almost
exclusively on large mammal hunting. Examining this assertion in the light of new
data is prudent.
In the discussion below I examine the basic animal and plant ecology of tropical
grasslands by comparing tropical grasslands
with several cold and temperate grassland
ecosystems. The comparative sample derives from those areas where good ethnographic data are available on hunter – gatherer adaptations. I am restricting the sample
in this way because the ultimate goal is to
relate plant and animal ecology to known
foraging adaptations. The cold grassland
sample is restricted to the ecosystems of the
two major Eskimo groups that focused entirely on terrestrial resources: the tundra
ecosystem to the north of the Brooks range
in Alaska (Nunamiut Eskimo), and the ‘‘barren grounds’’ ecosystem west of the Hudson
Bay (Asiqmiut or ‘‘Caribou Eskimo’’). The
temperate grassland sample includes the
Great Plains and the Great Basin-Plateau.
The Great Plains vary from tall grass to a
short grass prairie, but in all areas grasses
are the dominant plants (Coupland 1992).
The Great Basin-Plateau is sometimes classified as an ‘‘Intermountain Grassland’’ because it is used as rangeland (Brown 1989);
however, sagebrush (in the daisy family) is
the dominant plant species while the predominant grasses are bunch grasses. I include the Great Basin-Plateau in this analysis as it provides a useful comparison to the
arid grasslands of the tropics.
Mammal species richness (number of species) increases with decreasing latitude
(Krebs 1978; Pianka 1966; Rosenzweig 1992),
which suggests that large mammal richness
would also be greater in tropical grasslands
than in temperate and cold grasslands. Figure 1 and Table 1 show the large mammal
species richness in several tropical, cold, and
temperate grasslands from the sample regions. The sample of African grasslands includes two types of grasslands: edaphic
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TROPICAL GRASSLAND HUNTER – GATHERERS
grasslands (Kafue and Rukwa) and secondary grasslands (Serengeti and Athi-Kapiti
Plains). Edaphic or natural grasslands form
when the succession to more woody growth
has been arrested by biotic mechanisms such
as water-logging or root-resistant soil formations. Secondary or derived grasslands are
typically maintained by fire, often resulting
from the activity of people (Vesey-Fitzgerald
1963, 1973). Tropical African grasslands
have more diverse large mammal (Cole
1986), reptile (Barbault 1983) and bird (Fry
1983) faunas than other tropical grasslands
and thus may not represent tropical grasslands worldwide. I have not placed extinct
grassland ecosystems on Fig. 1 because it is
not possible to place all species in the habitat
categories confidently. One of the best
known extinct grassland ecosystems, the
Mammoth Steppe, had a species richness
above both extant cold and temperate grasslands but still significantly below tropical
African grasslands (Guthrie 1990).
Figure 1 shows that tropical African grasslands have more species of both mobile and
resident large herbivores (5 kg or greater in
body weight) than higher latitude grasslands. The residents may be important to
hunter – gatherers as their yearlong availability would dampen the wide seasonal
variation in mammal availability, resulting
from migration, that is so typical of temperate and cold grassland ecosystems. Some
predominantly migratory species, such as
Thomson’s gazelle (Gazella thomsoni), also
have subpopulations that do not migrate.
Such territorial individuals have shorter
flight distances (the distance between prey
and predator that results in prey flight) than
nonterritorial individuals (Walther 1995),
making them easier targets for predators.
The migrations in tropical African grasslands typically involve a succession of animals spread over several months, facilitating
niche separation and accommodating the
high diversity of migratory species. Successions of this type are present in both second-
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FIG. 1. The number of migratory/mobile and resident large ungulates in a sample of cold, temperate,
and moist tropical grasslands that were inhabited by
hunter – gatherers.
ary (Bell 1969, 1971) and edaphic (Sheppe
and Osborne 1971; Vesey-Fitzgerald 1964)
grassland ecosystems. These successions begin with one species that can tolerate the
more fibrous tops of grass plants and then
other species move in as their particular
plant part is made available through the actions of the prior feeders. Succession systems increase the time that a region can support a migratory population and may thus
increase the temporal availability of large
herbivores in tropical grasslands relative to
migration systems that lack successions.
Successions are absent or poorly developed
in modern cold and temperate grasslands,
though Guthrie (1990) has argued for such
a succession in Pleistocene steppes.
Tropical grasslands have a higher biomass
and net primary productivity than cold or
temperate grasslands (Whittaker and Likens
1973) and consequently tropical African
grasslands also have a greater biomass of
large ungulates than temperate grasslands
(De Vos 1969; Coupland 1993). As the majority of this biomass is composed of large herbivores (Coupland 1993), it is reasonable to
assert that the biomass of both mobile and
resident large mammals is higher in tropical
African grasslands than either temperate or
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Brown (1989)
Weaver (1956)
Sinclair (1972)
Sinclair (1977)
Great Plains
Serengeti
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27
6
4
Brown (1989)
Great Basin
3
2
Campbell (1968)
Pielou (1994)
Citation
Barren Grounds
Steppe
Birket-Smith (1929)
Pielou (1994)
Brooks Range
Tundra
Locality
Number of
species
Buffalo
Thomson’s
gazelle
Wildebeest
Zebra
Bison
Pronghorn
antelope
Pronghorn
antelope
Caribou
Caribou
Major
migrants
Eland
Elephant
Hartebeest
Oryx
Topi
Wapiti
Wapiti
Minor
migrants
Highly mobile
Black rhino
Buffalo
Grant’s gazelle
Giraffe
Hartebeest
Oribi
Ostrich
Thomson’s gazelle
Topi
Warthog
Wildebeest
Zebra
Bison
Pronghorn antelope
Muskox
Muskox
Resident or smallscale movement on
grasslands
Bohor reedbuck
Hippopotamus
Waterbuck
Resident Edaphic
grassland
Bushbuck
Bush duiker
Bushpig
Dik dik
Steinbok
Mule deer
White-tailed deer
Mule deer
White-tailed deer
Wapiti
Resident
Riparian
woodland
Klipspringer
Mountain
reedbuck
Dall sheep
Specialist of hills
and inselbergs
Resident or small-scale movement
TABLE 1
The Mobility Status and Presence in Microhabitats of the Large Animal Species in a Sample of Grassland Ecosystems
Buffalo
Bush duiker
Bushpig
Dik dik
Impala
Steinbok
Mule deer
Wapiti
Mule deer
White-tailed deer
Wapiti
Moose
Resident woodland/
grassland edge
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CURTIS W. MAREAN
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Sheppe and
Osborne (1971)
Vesey-Fitzgerald
(1964)
Foster and Coe
(1968)
Stewart and
Zaphiro (1963)
22
18
16
Lechwe
Wildebeest
Zebra
Buffalo
Elephant
Topi
Zebra
Hartebeest
Wildebeest
Zebra
Buffalo
Eland
Impala
Puku
Roan
Eland
Lichenstein’s
hartebeest
Roan
Eland
Thomson’s
gazelle
Å Edaphic
Å Edaphic
Giraffe
Grant’s gazelle
Ostrich
Rhino
Warthog
Hippopotamus
Common reedbuck
Sitatunga
Warthog
Waterbuck
Bohor reedbuck
Hippopotamus
Puku
Waterbuck
Bohor reedbuck
Hippopotamus
Waterbuck
None present
None present
Bushbuck
Bush duiker
Steinbok
None present
None present
Klipspringer
Mountain
reedbuck
Bushbuck
Bush duiker
Bushpig
Hartebeest
Impala
Kudu
Oribi
Sable
Steinbok
Bushbuck
Bush duiker
Giraffe
Impala
Steinbok
Warthog
Bushbuck
Bush duiker
Bushpig
Impala
Steinbok
Note that a species may be both migratory and resident as some species, such as Thomson’s gazelle, often have two subpopulations; one migrates and the other
does not. Some flexible species may occur in several microhabitats. The classification in this table is collapsed into Fig. 1.
Kafue River
Floodplain
Rukwa Valley
Athi-Kapiti
Plains
TROPICAL GRASSLAND HUNTER – GATHERERS
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FIG. 2. The number of edible plant species used by
several hunter – gatherer groups that inhabited or inhabit cold, temperate, and tropical grasslands.
cold grasslands. In summary, tropical African grasslands have a greater abundance of
large herbivores, greater diversity of large
herbivores, greater abundance and diversity
of residential large herbivores, and a longer
temporally extended grazing succession.
In Fig. 2 and Table 2 I have extracted from
the ethnographic literature the number of
plant species used for food by hunter – gatherer groups occupying cold and temperate
grasslands and African tropical grasslands.
This is not an estimate of the total number
of edible plants available, but a list of those
plant species productive enough to warrant
inclusion in the diet of the hunter – gatherers
present in those environments. As noted before, we have few observations of hunter –
gatherers in moist tropical grasslands and
several observations of hunter – gatherers in
arid grasslands. I have included these arid
grassland hunter – gatherers (the various San
groups of the Kalahari) and also one hunter –
gatherer group (the Suiei Dorobo) that use
an East African grassland that receives about
620 mm of rainfall annually. The plant food
collection of Eskimo is well documented as
negligible. For example, the Tuluaqmiut Nunamiut used only 12 species of plants
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(Campbell 1968), Stoney (1900) records the
use of 22 species of plants among Kuuvakmiut Eskimo (these are neither Nunamiut
or Caribou Eskimo, however), and BirketSmith (1929) records the use of just 6 species
of plants among the Caribou Eskimo.
Figure 2 shows that the African hunter –
gatherers generally use a larger variety of
edible plant foods than hunter – gatherers in
cold and temperate grasslands. The Great
Plains groups are remarkably consistent in
the variety of species used, which suggests
collection at the maximum available species
richness in those temperate grasslands. The
Great Plains Indians exploited far fewer
USO plants than tropical grassland hunter –
gatherers. A more effective measure would
be the total calories exploited, as the Great
Plains Indians clearly obtained large quantities of Psoralea esculenta (the Plains turnip,
Reid 1977; Kaye and Moodie 1978), but those
data are not available. The arid tropical
grassland hunter – gatherers use and presumably have access to more USO species
than in moister grasslands, though these are
environments more arid than the environments of interest here. The Suiei Dorobo,
however, do provide some useful observations. Suiei collect 122 plant species (Ichikawa 1980), 69 of which are fruits, and plant
foods make up most of their diet, unlike
most other Dorobo/Okiek (Blackburn 1982).
Of the 122 plant species, 92 are found in the
grasslands. Of the 10 staple plant species, 6
are found in grasslands (Ichikawa 1980). The
Suiei data are inconsistent with Foley’s expectations of a diet lacking in plant foods in
tropical grasslands receiving more than 500
mm of annual rainfall.
USOs (rhizomes, tubers, corms, and
bulbs) are favorites of hunter – gatherers because the often massive storage organs are
large carbohydrate packages (Gott 1982;
Harrington 1967; Vincent 1985a and 1985b).
Figure 3A shows the species richness of
USOs in several African regions as summarized by Vincent (1985b) plotted against
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TABLE 2
The Number of Plant Species Exploited as Food in the Great Basin, the Great Plains, and Africa
Greens
Fruits,
berries,
nut, plum
Gum
Sum
Reference
Steward (1938)
Steward (1938)
Steward (1938),
Chamberlin
(1911)
Steward (1938)
USOs
Melons
Pods,
beans
5
9
8
0
0
0
0
0
0
41
13
47
4
?
12
5
7
12
0
0
0
54
29
81
Lemhi
Great Plains
Cheyenne
Blackfoot
20
0
0
13
2
3
0
38
10
8
0
0
1
0
0
0
2
10
18
15
0
1
31
34
Comanche
13
0
1
0
0
20
0
34
8
0
2
4
5
15
0
34
Grinnell (1915)
Hellson and
Gadd (1974)
Carlson and
Jones (1939)
Gilmore (1919)
24
41
35
18
2
2
2
0
2
3
3
4
4
2
0
5
4
6
24
23
22
29
12
69
11
18
9
5
69
101
85
122
Marshall (1976)
Lee (1979)
Tanaka (1976)
Ichikawa (1980)
Great Basin
Owens Valley
Reese River
Gosiute
Missouri River
Africa
!Kung of Nyae Nyae
Dobe !Kung
Central Kalahari
Suiei Dorobo
Seeds
Note. Not all cited sources classified plants in the same way so the author moved some species to other categories
to increase consistency. The data from the Missouri River Region are a compilation of the foods eaten by several
groups. The ‘Sum’ includes species not classified on the table.
mean annual rainfall, and Table 3 gives the
raw data with further contextual elaboration. These data show that no tendency exists for USO species richness to decline
where rainfall lies between 500 and 1000 mm
(contra Foley 1982), and the relative frequency of USOs as a component of all plant
species (Fig. 3B) increases linearly with rainfall values between 100 and 1000 mm. These
data also indicate Foley’s (1982) 500 mm
rainfall threshold is not substantiated. In addition, the data reveal a soil nutrient effect.
Localities on soils derived from granitic parent material, and thus low in nutrients, tend
to have more USO species for a given
amount of rainfall than localities with high
nutrient volcanic-derived soils. Thus it appears that soil nutrient status and rainfall
interact to determine USO species richness.
Though few data exist on the edibility and
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density of these USO species, most tropical
African USOs are edible either without processing or with minimal processing (Vincent
1985a, 1985b).
As mentioned earlier, grasslands are heterogeneous ecosystems that contain many
small microhabitats conditioned by variations in geology, soil catena, and drainage.
USOs typically require well-drained soils
and thrive in dry conditions. In a study of
the distribution of USOs near Lake Eyasi
and Lake Manyara in Tanzania, Vincent
(1985a, 1985b) found that USOs are most
abundant high on the catena on the slopes
of escarpments and inselbergs, and least
abundant in moist soils of forests and
edaphic grasslands. Though well-drained
secondary grasslands may have several species of USOs, the density and species richness of USOs clearly declines from the well-
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FIG. 3. The number of USO plant species plotted
against mean annual rainfall (A), and the percentage of
all plant species that have USOs plotted against mean
annual rainfall (B), for several African ecosystems. The
circles represent localities on low-nutrient basement
rocks, and the triangles represent localities on high-nutrient volcanic rocks.
drained top of the soil catena to the poorly
drained bottom. This is also the case for the
distribution of USOs on temperate grasslands (Kaye and Berry 1978; Kuhn 1987; Reid
1977). USOs typically occur in distinct
patches forming from compound clusters or
root propagation. Importantly, tropical USO
species can be edible year-round although
they do undergo changes in their nutritional
value (Gott 1982; Vincent 1985a, 1985b).
Temperate grassland USOs have much
stricter seasonal cycles that depress their
palatability and visibility (Kuhn 1987). Vincent found that East African USOs tend to
be nutritious and palatable year-round, and
importantly they retain their above-ground
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shoots year-round, allowing them to be discovered more easily and consistently (Vincent 1985a, 1985b). The less seasonal character of USOs in tropical African grasslands is
a key ecological distinction relative to higher
latitude grasslands.
Plant foods that grow above ground
(AGPs), such as fruits, berries, nuts, greens,
and seeds, are generally found on woody
growth, and woody growth typically requires well-drained soils with regular access
to moisture. In grasslands woody growth occurs on levees near seasonally flooded
streams and lakes (gallery forest) or higher
on the soil catena. Sept quantified the abundance of edible plant foods near the Voi
River in Tsavo East (Kenya), an arid channel
that drains into Lake Turkana (Kenya), in
the Parc National des Virunga in the upper
Semliki Valley (Zaire), and along the Ishasha
River in Zaire (Sept 1984, 1986, 1990, 1994).
Sept has found that fleshy fruits occur in
abundance along rivers and streams. More
specifically, on the proximal margins of
streams the soils are well drained and covered with gallery forest that includes many
species of fruit-bearing plants. On the poorly
drained distal margins edaphic grasslands
are present while collectable fruits are rare.
Overall, Sept’s data show that within tropical grassland ecosystems microhabitats contain significant quantities of edible plants
that grow above ground.
The data discussed above, derived from
ethnography and Vincent’s and Sept’s studies of edible plant availability, are qualitatively summarized in Table 4. These data
show that tropical African grasslands are
much richer in plant foods than originally
portrayed by Foley (1982). Tropical grasslands have a higher species richness and
higher biomass of mobile and resident large
mammals than either temperate grasslands
or cold grasslands. The mobile large mammals are a patchy resource spatially (they
occur in dense herds), temporally unpredictable (the herds have regular routes but the
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TROPICAL GRASSLAND HUNTER – GATHERERS
TABLE 3
The Number of USO Plant Species by Locality in East Africa
Locality
Habitat type
Annual
rainfall
Mau Forest
Mbeya Range
Gombe National Park
Mahale Mountains
West Usambara
Lake Manyara
North-East Serengeti
Meru National Park
Ruaha National Park
Simanjaro Plain
Tsavo East National Park
Marsabit
South-west Marsabit
Lake Turkana
Montane Forest
Montane Forest
Brachystegia Woodland
Brachystegia Woodland
Montane Forest
Acacia, Woodland
Wooded Grassland
Wooded Grassland
Wooded Grassland
Bushed Grassland
Bushland and Acacia
Semi-desert
Semi-desert
Semi-desert
1750
1750
1500
1500
1425
950
900
710
650
600
546
250
150
250
Soil parent
material
Number of
USO
species
Percentage of
all species that
are USOs
Volcanic
Basement
Basement
Basement
Basement
Volcanic
Volcanic
Volcanic
Basement
Volcanic
Basement
Basement
Volcanic
Volcanic
31
14
57
29
2
74
68
54
255
29
93
119
55
40
6.3
5.9
10
4.6
2
13.1
19.7
11.9
19.3
14.7
11.3
10
8.9
7.8
Note. Soil parent material data are taken from maps of the Geological Survey of Kenya and Tanzania. All other
data are from Vincent (1985b).
timing and exact placement are typically
variable), and seasonal in availability. The
resident large mammals are also patchy
(most occur in bushy or wooded micro habitats in grasslands), but temporally and spatially predictable, and not seasonal. Tropical
African grasslands, at least up to 1000 mm
of annual rainfall, have a higher species richness of plants with USOs than either temperate or cold grasslands. These USOs are a rich
source of carbohydrate, they are patchily
distributed, temporally and spatially predictable, and not as seasonal as AGPs. AGPs
are also diverse in tropical African grasslands. They are patchily distributed, temporally and spatially predictable, and very seasonal. Overall, carbohydrate and protein
availability in tropical grasslands is less seasonal than in temperate and cold grasslands
and this is of critical importance to under-
TABLE 4
Qualitative Summary of the Major Ecological Parameters Relevant to Foraging
in Tropical, Temperate, and Cold Grasslands
Large mammal biomass
Large mammal species richness
Resident large mammal species richness
Mobile large mammal species richness
Seasonality of large mammal availability
Edible plant species richness
USO species richness
AGP species richness
Seasonality of plant availability
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Tropical
Temperate
Cold
High
High
High
High
Moderate
High
High
High
Low
Moderate
Low
Low
Low
High
Moderate
Low
Moderate
High
Low
Low
Low
Low
High
Low
Low
Low
High
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CURTIS W. MAREAN
standing hunter – gatherer adaptations to
tropical grasslands relative to cold and temperate grasslands. Cold, temperate, and
tropical grasslands experience dramatic seasonal fluctuations in precipitation, but tropical grasslands experience seasonal variations that are near zero degrees in mean
daily temperature while temperate grasslands experience fluctuations up to 407C
(Ripley 1992). This may be the causative
mechanism underlying the greater diversity
and less seasonal character to plant and animal availability in tropical grasslands.
HUNTER–GATHERER HUNTING
STRATEGIES IN GRASSLANDS
The discussion above highlighted the biotic distinctions important to foraging strategies in cold, temperate, and tropical African
grasslands. These distinctions can be used
to develop models of hunter – gatherer plant
and animal exploitation in tropical African
grasslands. One way to accomplish this is to
focus on the way that temperate and cold
grassland hunter – gatherers adapted to the
particular problems posed by their grasslands. If these problems are similar to those
posed by tropical African grasslands, we
may hypothesize a similar adaptation modified to account for other contingencies.
Any attempt to model hunting strategies
must consider the important distinctions between cold/temperate grasslands and tropical African grasslands in plant food availability. Cold and temperate grasslands pose
difficult problems. From early winter to
early spring few if any plant foods are available and thus the potential menu is low in
high quality calories (Speth 1983; Speth and
Spielman 1983). Most of the plant foods that
are available during the warm months are
small items (nuts, berries, seeds, etc.), patchily distributed, productive for only a few
months, often unpredictable, and may require intensive collecting or processing
strategies. An obvious strategy to compen-
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sate for seasonal scarcity of plant foods is to
switch to animal foods. However, in grasslands prey animals are typically migratory
and thus only available in quantity during
short periods of the year. Many of these animals are in poor condition and lack the necessary fat to compensate people for the loss
of plant carbohydrate (Speth 1983; Speth and
Spielman 1983). Many cold and temperate
grassland hunter – gatherers designed similar strategies to cope with such problems.
The data discussed above, however, suggest
that tropical African grasslands do not suffer
the striking seasonal dearth of carbohydrate
so typical of temperate and cold grasslands.
Before discussing the strategies, it is useful
to break apart the various components of a
hunting strategy so that each component can
be directly related to specific ecological conditions.
Components of a Hunting Strategy
A hunting strategy is usefully understood as a composite of encounter techniques, prey choice techniques, and organizational techniques. The encounter technique can include various combinations of
routed or encounter hunting, intercept
hunting, passive use of stationary traps
such as snares and pitfalls, and an active
use of traps that I will call tactical landscape methods. These traps may be natural
features of the landscape such as gullies,
cliffs, or box canyons, or they may be stationary installations people have built on
the landscape, or a combination of the two.
Traps used in tactical methods may even
be mobile, such as strings of nets held by
people. Tactical methods are an approach
to hunting where the landscape becomes a
weapon, people have a dynamic role in the
operation of the weapon, effective operation usually involves high search costs
(particularly high when people modify the
landscape) and handling costs, and de-
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tailed planning and organization is critical
for success.
The prey choice technique spans a continuum
from specialized hunting, which includes a
very narrow choice of species relative to the
natural species richness of a region, to generalized hunting, which includes a wider choice of
species. Hunters may oscillate seasonally between specialized and generalized hunting.
Specialized hunting typically involves a strategy where one species, or two, is targeted as
the main prey item, while other species are
ignored. Specialized hunting in grasslands is
often, perhaps always, joined to tactical methods, as is discussed below. The reverse, however, may not be true as tactical methods could
result in kills of several prey species, particularly in environments where grassland species
co-associate (such as in many African grasslands). The Mbuti pygmy net surrounds do not
result in a specialized species yield, yet these
are clearly tactical methods (Ichikawa 1983).
The organizational technique can include a
single hunter, several hunters, or communal
hunting by large groups. Grassland hunters
using tactical methods typically employ
communal hunts, as is discussed below.
However, communal hunting need not always result in specialized prey choice. Communal hunts may not always be executed
with tactical methods. Thus, some of the
three components of a hunting strategy are
casually linked in an inflexible way, while
most components occur in various permutations. The ethnographic literature discussed
below suggests that specialized hunting
may be an example of the former — it may
typically be implemented with communal
hunting using tactical methods.
My primary concern here is the relation
between different components of a hunting
strategy, the character of animal prey (biomass, species richness, and movement patterns) the strategy is meant to exploit, and
the affects plant food availability have
on the hunting strategy hunter – gatherers
choose to use. In other words, are there regu-
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larities in the relationship between prey
characteristics, the techniques used to capture the prey, and the availability of plant
foods? Such regularities can be used to construct models for hunting strategies in tropical African grasslands when one takes into
consideration two important points discussed earlier: (1) plants foods are more
abundant and less seasonal in tropical grasslands, and (2) species richness and biomass
of migratory and residential ungulates are
higher in tropical grasslands. The significance of this will become clear below when
I construct likely hunting models for tropical
African grasslands.
Hunting Strategies in Cold and Temperate
Grasslands
The rich ethnographic literature on hunting strategies among cold grassland hunters
in North America shows that tactical landscape methods were preferred for killing the
primary grassland animal, the caribou.
These methods are the same as those referred to by Burch (1972) as ‘‘head-’em-offat-the-pass’’ techniques. All Eskimo groups
used various tactical landscape methods
such as driving caribou into rivers, lakes,
and streams and then dispatching them
from a boat (Birket-Smith 1929; Boas 1888;
Cantwell in Healey 1889; Gubser 1965; Spencer 1959; Stoney 1900) and intercepting and
driving caribou into box canyons, valleys,
constructed traps, and corrals (Binford 1978;
Birket-Smith 1929; Boas 1988; Cantwell in
Healey 1889; Gubser 1965; Ingstad 1954; Jenness 1928; Spencer 1959; Stoney 1900). Our
main interest here is on those groups that
relied solely on the food resources of the
cold grasslands (the Caribou and Nunamiut
Eskimo) and the ethnographic literature is
clear that tactical techniques combined with
communal hunting were the primary methods for killing caribou. Many authors are
explicit about the communal nature of these
hunts, for example: ‘‘The great spring hunt
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CURTIS W. MAREAN
was undertaken by means of one or two
well-defined methods involving activity on
the part of virtually every member of the
community’’ (Spencer 1959: 29). The many
descriptions of corrals, enclosures, and
fences show that a huge effort was expended
to make and maintain such installations (Birket-Smith 1929; Cantwell in Healey 1889; Ingstad 1954; Spencer 1959; Stoney 1900).
Routed or encounter hunts, referred to by
Burch (1972) as ‘‘search-and-destroy techniques,’’ were used occasionally, more so
among groups more dependent on marine
resources, but most of the sources are clear
that this method was a minor contributor
to the diet of the Caribou and Nunamiut
Eskimo.
Though caribou formed the major component of the diet of Nunamiut and Caribou
Eskimo, other terrestrial species were significant. The Nunamiut commonly hunted
other large herbivores, including the Dall
sheep (the second most hunted species), the
moose, and probably the musk ox before its
virtual extinction. Bears (black and grizzly)
were a rare but important component of the
Nunamiut diet, as were a variety of smaller
mammals including snowshoe hare, red
squirrel, beaver, and arctic ground squirrel
(Binford 1978; Campbell 1968; Gubser 1965;
Spencer 1959). The Caribou Eskimo did not
have access to Dall sheep and moose and
therefore were more dependent on caribou
(Birket-Smith 1929).
The ethnographic literature on temperate
grassland hunter – gatherers is rich but complicated. One complication is that many
eastern Plains Indians, particularly in the
Missouri valley, also practiced agriculture
and traded extensively for agricultural products (Lowie 1963). Another complication is
that the introduction of the horse had a significant impact on the bison procurement
strategies of the Plains Indians (Anell 1969;
Ewers 1958; Roe 1955). My main interest
here is on the pre-horse strategies of the nonagricultural groups. Although most obser-
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vations of Plains Indian bison hunting were
made after the introduction of the horse,
there are several observations of pre-horse
hunting in the northern Plains, where the
horse was introduced the latest. Also, in
many areas researchers interviewed individuals who had hunted before the introduction
of the horse (for example the Cheyenne
studied by Grinnell [1915]), or knew tales of
the pre-horse times.
The Plains Indian literature clearly shows
that tactical landscape methods were the
preferred encounter techniques for bison before the introduction of the horse. Though
Plains Indian tactical landscape methods
may superficially appear homogeneous, a
variety of methods were used under different contingencies. Grinnell (1915) described
foot surrounds by many hunters armed with
bows, from discussions with Cheyenne in
the late 1800s. He also described the use of
a bluff or cutbank where the wall was used
as one side of a pen with the pen being finished off with bush and wood. Lines of
bushes extended from the entrance of the
pen like wings of a chute onto the plains.
Ewers (1949, 1955) described several Blackfoot tactical techniques for hunting bison, all
of which had one distinguishing feature; the
bison were driven between converging
fences made of rows of cairns or people acting as beaters. These V-shaped lines ended
in either a corral on level ground, a sunken
corral meant to break the legs of the bison,
or a very steep precipice.
Anell (1969) compiled observations of the
Plains Indian use of pounds and enclosures
for killing bison. The pound was a substantial structure whose construction entailed
significant labor costs. It was usually circular
and made of logs, stones, and other materials and was built high enough to keep the
animals from seeing over the top. The pound
was reached by only one entrance of converging fences designed to be high and
dense enough to conceal the hunters. The
bison were driven in by beaters or lured in.
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TROPICAL GRASSLAND HUNTER – GATHERERS
Once inside, those animals that survived the
tumult were shot by arrows. Such substantial pounds were reportedly used by the
Blackfoot (Grinnell 1915), and Hind (1860)
provides a graphic description of the results
of a pound-hunt by the Cree. Grinnell (1915)
also describes Cheyenne hunting pronghorn
antelope using pits placed near the convergence of two streams, supplemented by
bush borders. Antelope were driven between the streams into the pits.
The evidence discussed above shows that
tactical landscape methods were the predominant encounter technique when hunting mobile grassland species such as bison,
caribou, and pronghorn antelope in cold and
temperate grasslands. Communal hunting
was the preferred organizational technique
for such tactical hunts. Many hunts included
substantial landscape installations that required significant labor investments to build
and maintain, thus driving up search and
handling costs. Centering a hunting strategy
around tactical hunts, with the associated
costs of building and maintaining landscape
installations and aggregating large numbers
of people, is probably risky for several reasons (Frison 1991). First, migratory species
can be prone to a boom and bust demographic pattern, and often the precipitous
drop in population occurs suddenly. The
large Alaskan caribou herds have undergone several population crashes (Burch
1972; Haber 1977) that placed enormous
stress on the Eskimo (Burch 1972). The populations of African migratory species such
as wildebeest can be quickly decimated by
droughts, flooding rains, and disease (Foster
and Coe 1967; Stewart and Zaphiro, 1963).
Second, migrations pass through a region
over a limited period of time, and the ethnographic literature discussed above suggests
that there is a narrow window of time within
which such hunts can occur. Failure to be
successful in a tactical hunt expends a large
portion of this window of time, and the costs
associated with the failed attempt are high.
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If tactical methods are risky, then this raises
a question critical to building models for
tropical grassland hunters. Why did temperate and cold grassland hunters use tactical
and communal techniques when these techniques were clearly expensive and risky?
Three different explanations can be suggested; two based in behavioral ecology and
the third more social in causation.
The first possible explanation is that tactical techniques are the optimal strategy for
procuring mobile large prey in open highvisibility environments. If this is true, then
tropical grassland hunter – gatherers may
also have used such techniques simply because of the similar predominance of large
mobile herbivores in open environments.
The alternative ecological explanation is that
tactical strategies are a response to nutritional deficits caused by the low species richness, low biomass, and seasonally punctuated availability of plant foods in temperate
and cold grasslands. It could be argued that
tactical communal hunting strategies were
designed to overcome the nutritional problems caused by the complete lack of collectable plant foods winter through spring. Low
animal species richness, combined with
highly mobile prey, results in one or two
seasonal windows of opportunity for attaining enough food for the year. Given this,
people in cold and temperate grasslands had
no choice but to use a hunting strategy that
involved tactical hunts with the chance of
decisive success and consequent surplus.
This need for surplus is a common argument
for explaining Great Plains communal hunts
(Frison 1991). As shown earlier, tropical African grasslands do not share with cold and
temperate grasslands the problem of highly
seasonal food availability as tropical African
grasslands have a regular availability of a
diversity of residential large mammals and
a less seasonal quality of USO availability
and palatability. If tactical techniques are a
response to seasonal caloric deficits, then we
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CURTIS W. MAREAN
may not expect tactical hunting in tropical
African grasslands.
A third explanation for large communal
hunts in grasslands is that these hunts are
necessary to provision large aggregations of
people that congregate for social reasons.
Fawcett (1987) has proposed this as an explanation for Great Plains communal hunting in response to alleged inconsistencies in
the more ecologically grounded explanations of Frison (1970, 1991) and Speth (1983).
This explanation is not necessarily unique to
grasslands as any large aggregation of people in any environment may stimulate a
need for communal hunting. This interpretation may be correct for specific cases, however I find it unpersuasive as a general theory. The vast majority of temperate and cold
grassland hunter – gatherers regularly practiced communal hunting, and for this hypothesis to be compelling as a general theory
one must posit that all these groups were
driven to aggregate for social reasons and
only hunted communally during such special aggregations. Caribou and Nunamiut
Eskimo practiced communal hunts but these
were not associated with special seasonal
aggregations of people — they were timed to
coincide with the movement of caribou and
typically carried out with the core group.
Some specific cases of communal hunting
are likely to result from the need to provision large aggregations of people for social
reasons, but a general explanation for the
prevalence of communal tactical hunts in
temperate and cold grasslands most likely
is found in one of the two ecological explanations.
THREE MODELS FOR TROPICAL
GRASSLAND FORAGING
The discussion above leads to several alternative models of adaptations for hunter –
gatherers in moist tropical African grasslands. I will describe these below, beginning
with what I think is the most likely model
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based on the similarities and distinctions between moist tropical African grasslands and
cold and temperate grasslands. I will assume
that the hunter – gatherers are exploiting the
grasslands all year, however each model
could easily accommodate a seasonal mobility component where the hunter – gatherers
move off the grasslands into the woodlands.
The models have many behavioral predictions with archaeological test implications.
Here, however, I will focus on those aspects
of the models that can be examined with
the zooarchaeological data that are currently
available.
The Generalized Grassland Model is derived
primarily from the biotic dissimilarities between moist tropical African grasslands and
cold and temperate grasslands, particularly
in regards to the availability of edible plants
and residential ungulates. It differs from the
pattern documented by ethnography for
hunter – gatherers living in cold and temperate grasslands. This model predicts that
plant foods dominate the diet breadth and
contribute the majority of calories to the diet.
The lack of dramatic seasonal variation in
plant food availability, and the abundance of
residential mammals, combine to ameliorate
seasonal fluctuations in food. Thus this
model predicts that tropical grassland
hunter – gatherers will never use tactical
landscape methods. The model assumes that
tactical methods are used to overcome seasonal caloric deficits, and that tactical methods are not necessarily the most efficient
open habitat hunting techniques.
The lack of tactical hunts will cancel the
need for large communal aggregations, and
the primary organizational hunting technique will be individual or small group
hunting. Large aggregations have distinct
costs in that plant and animal foods are rapidly exhausted within the foraging radius of
an aggregated group. However, it is possible
that people may aggregate due to environmental constraints, such as around water
holes during the dry season, or for social
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TROPICAL GRASSLAND HUNTER – GATHERERS
reasons. The primary hunting techniques
will include various combinations of routed
hunting, passive trapping, and intercept
hunting at water holes, riparian woodlands,
salt licks, and other natural magnets for
mammals. The species choice will be very
broad, sampling migrants and residents,
large and small animals. Residential sites
should show high species richness as these
sites are the end points for transportation
from many encounter sites. We should not
find open-air sites with the characteristics
typical of mass-kills. The generalized strategies well described for the various arid
grassland groups, such as the Khoi San and
Hadza, fall within this model. This strategy
is within the forager range of Binford’s
(1980) forager/collector continuum. Given
the ecological conditions of tropical grasslands, this is the preferred model for East
Africa.
The Seasonal Grassland Model differs from
the Generalized Grassland Model in that it
suggests that tactical hunting techniques
should be used at least seasonally. This
model assumes that tactical techniques are
the most efficient technique for killing large
mobile ungulates in grasslands. During certain seasons of the year large herds of ungulates pass through on their seasonal round,
as in the Serengeti, or concentrate in wellwatered areas if the ungulates practice an
aggregation-dispersal strategy, as in Amboseli. During these seasons of encounter, the
use of tactical techniques raises the return
rates of migratory animals so that migratory
animals are regularly hunted. Other hunter –
gatherer groups may move to converge on
these natural points of animal aggregation
and thus natural aggregations of people may
form. Alternatively, people may aggregate
for the specific purpose of producing larger
more effective groups for communal hunting. Smaller resident ungulates will probably be ignored as their return rates are typically lower than for larger ungulates
(Hawkes, O’Connell, and Blurton-Jones
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1991). It is likely that large aggregated
groups would rapidly exhaust plant foods
within the foraging radius of the aggregation sites as even small groups of Central
Kalahari San (Tanaka 1980) and Hadza
(Woodburn 1968) exploit the plant foods
within their foraging radius sufficiently to
stimulate a residential move within days or
weeks. For this reason plant foods would
probably not be a major food item. During
such aggregation seasons the hunting strategy should be characterized by a single species focus and communal hunts.
During the rest of the year, when migrants
are not concentrated in the region, the foraging strategy should shift to the Generalized
Grassland Model and plant foods and resident ungulates will once again rise in resource rank. Thus the Seasonal Model posits
a seasonally shifting forager/collector strategy. With the Seasonal Model at least some
hunting sites will be locations characterized
by very low species richness because drives
of animals in grasslands are typically focused on one species (Frison 1991). In Africa,
however, migratory species have a tendency
to co-associate (such as wildebeest and zebra, Thomson’s gazelle and Grant’s gazelle),
and thus mass kills are likely to have several
species, unlike the bison and caribou mass
kill sites in North America. These hunting
sites will also display a seasonal signature
in the mortality profiles as animals are killed
at that location at restricted times of the year.
Such sites should be strategically placed to
make the driving process easier, and landscape modifications may be present. Residential sites occupied only during the tactical hunts will show a specialized species
choice. Residential sites occupied throughout the year will show a generalized species
choice.
The Specialized Grassland Model, considered the least likely for tropical grasslands,
is based on the basic abiotic and biotic similarities between the temperate grasslands
and moist tropical African grasslands. In es-
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CURTIS W. MAREAN
sence, this is a Great Plains Indian strategy
transferred to the African plains and adjusted for the ecological dissimilarities between tropical and temperate grasslands.
This model assumes that grassland ecosystems are best exploited with a specialized
hunting strategy including tactical landscape methods, communal hunting, and
specialized prey choice. Specialized hunts
employing tactical and communal methods
would be used whenever viable and these
hunts would be a major determining factor
in the yearly land-use strategy. This strategy
would posit a subsistence system based
around the drying and/or smoking of massive quantities of meat. Communal tactical
hunts would occur during seasons when the
migrations pass through or stabilize within
a region. The prolonged grazing successions
in tropical African grasslands would increase the time span, relative to temperate
grasslands, during which communal and
tactical hunts could be effective. Most kill
sites should be dominated by a few co-associating migratory species and the kill sites
should be at places strategic for tactical
hunts. During seasons when the migrants
are absent the hunter – gatherers should either switch to residential mammals and
plant foods, or move off the grasslands. Residential sites should show a very narrow
species richness focused on migratory species though residential sites may be more
species rich to account for occasional opportunistic kills.
ARCHAEOLOGICAL EVIDENCE FOR
GRASSLAND EXPLOITATION IN
EAST AFRICA
Archaeological research on the Middle
Stone Age (MSA) and the Later Stone Age
(LSA) is very spotty in East Africa, with
some centers of concentration in the Naivasha-Nakuru-Elmenteita basin and at Lukenya Hill (Fig. 4). Most other MSA and LSA
data in East Africa comes from scattered
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FIG. 4. Map showing East Africa and the location of
Lukenya Hill.
sites (such as Kisese II, Nasera Rockshelter,
Mumba-Höhle, Loiyangalani). The isolated
nature of these sites makes them poor candidates for investigating the hunting models
discussed above. Lukenya Hill is the only
locality that has several reasonably contemporaneous sites that were clearly occupied
by hunter – gatherers within a grassland ecosystem.
The Lukenya Hill Environmental Setting
Lukenya Hill is a gneissic inselberg that
rises to about 200 meters above the AthiKapiti Plains (Fig. 5). The inselberg measures about 8 km long to a maximum 2 km
wide. It varies from being a coarse-grained
soil-covered hill in some areas, to a rocky
jumble of detaching and eroding rocks that
form many cliffs, overhangs, shelters, and
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FIG. 5. Map showing the Lukenya Hill (in the dotted-line box that delimits the extent of Fig. 7) and
Athi-Kapiti Plains region; the position of major drainages, rivers, and streams; and the most common
path of the large mammal migration.
water trapments. Archaeological remains
are abundant on and around the hill, attesting to its attractiveness as a place of stone
age settlement. The Athi-Kapiti Plains and
Lukenya Hill lie in the semiarid region of
Kenya. Most of the region receives about 550
mm of rainfall per year, and the annual potential evaporation is high at 1500 to 2000
mm (Reed 1983).
The immediate region surrounding Lukenya Hill includes the Athi-Kapiti Plains
(1690 km2) and the Nairobi National Park
(112 km2). The Ngong Hills and the eastern
wall of the Rift Valley form a western
boundary to the region. To the south is a
rocky area of closed bush vegetation and the
Pelewa Hills, and the eastern boundary is
formed by the Selenkai River. The region
surrounding Lukenya Hill has four distinct
physiographic units: the high ground of the
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eastern flank of the Rift Valley including the
Ngong Hills (about 30 to 40 km west of Lukenya Hill), the Athi and Kapiti Plains (surrounding Lukenya Hill), the central hill
masses of the Machakos district (within 10
to 40 km east of Lukenya Hill), and the partially dissected peneplain including the
Yatta Plateau (about 50 to 60 km northeast
of Lukenya Hill).
The Athi-Kapiti Plains surround Lukenya
Hill and would have been critical to the occupants of the sites. Most of the plains consist of flat volcanics that lie between 1000
and 1500 m a.s.l. The Athi Plains are underlain mainly by phonolite, lava, and tuff and
tend to be flat and end in a bluff just west
of the Athi River. Several seasonal rivers and
streams traverse the Athi Plains flowing in
an easterly direction. The Kapiti Plains occur
east of the Athi River and the main underly-
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ing bedrock is an ancient metamorphic basement rock except along the western margin
underlain by the end of the Kapiti Phonolite
(Fairborn 1963). The topography of the Kapiti Plains is more varied than the Athi Plains,
being gently undulating to flat with many
small hills. No permanent rivers exist on the
Kapiti Plains, just seasonal streams with
short periods of flow. This geomorphic variety results in corresponding biotic diversity.
The rolling topography of the Athi-Kapiti
Plains shows a classic catenary pattern that
determines much of the variation in vegetation (Stelfox 1985; Stelfox and Hudson 1986).
There are three basic vegetation types in the
Athi-Kapiti plains, and the occurrence of
these types is primarily a product of topography and soil character. On the flatter
plains various grassland types occur but
they are dominated by dwarf tree ’whistling
thorn’ (Acacia drepanalobium) grassland.
Scrub lands with scattered bush with very
little grass occur on the flanks of hills and
on the exposed edges of lava flows where
one often finds a thin line of bush vegetation.
Riparian bush and woodland occur near the
incised river courses. The predominant vegetation types, using rangeland classification
(Pratt and Gwynne 1977), are primarily
grasslands and wooded grasslands.
The Athi-Kapiti Plains was once home to
huge numbers of animals. The Plains represent a complete ecological unit with very little movement of animals in or out, but there
is considerable internal movement stimulated by the degradation of rangeland conditions during the dry season (Stewart and
Zaphiro 1963). The populations of mammals
and the migration have been disrupted in
recent years by many factors related to human settlement (Foster and Coe, 1968). Despite the radical modifications to the local
region and the disruption of the migration,
reconstructing the migration pattern with
reasonable confidence is possible. Before
fencing in 1947, mammals migrated freely
in the dry season to permanent water in the
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FIG. 6. Census data from the Nairobi National Park
of the major grassland species on the Athi Plains. The
Nairobi National Park census samples only a small fraction of the mammals that comprise the Athi-Kapiti
Plains ecosystem, though the proportions are probably
reasonably similar.
Nairobi Park, the Ngong Hills, and to Thika
(Fig. 5). In the wet season the game dispersed to the plains.
Formal game censuses of Nairobi National
Park have been taken since 1961 (Fig. 6, from
Foster and Coe, 1967). A less rigorous census
was taken before 1961 (Stewart and Zaphiro,
1963). The evidence from these two sources
clearly shows that wildebeest (Connochaetes
taurinus) was the dominant ungulate in the
Athi-Kapiti Plains followed by Burchell’s zebra (Equus burchelli), hartebeest (Alcelaphus buselaphus), and impala (Aepyceros melampus).
Since 1961, due to increases in the population
of livestock, the effects of fencing, and the
drought of 1960–1961, the relative numbers
of animals in the Nairobi Park and in the
plains have changed. Most of the animals
shown in Fig. 6 are seasonal migrants. Members of the migratory species sometimes remain as residents as is true of Thomson’s gazelle. Species that are residents at the inselbergs include mountain reedbuck (Redunca
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fulvorufula), klipspringer (Oreotragus oreotragus), and steinbok (Raphicerus campestris). Bohor reedbuck (Redunca redunca), waterbuck
(Kobus ellipsiprymnus), hippo (Hippopotamus
amphibius), and crocodile (Crocodylus niloticus)
occur in or near the Athi River. This high density and species richness of large animals supported a large carnivore population, including
lions, leopards, hyenas, and jackals. The density of lions and large herbivores encountered
by Roosevelt (1910) attests to the richness of
this area for a hunter, both human and animal.
The Lukenya Hill Archaeological Record
Archaeologists have repeatedly investigated aspects of the prehistoric record at Lukenya Hill since 1970 (Barut 1994; Bower et
al. 1977; Bower and Nelson 1978; Gramly
1976; Gramly and Rightmire 1973; Marean
1990, 1992b; Marean and Gifford-Gonzalez
1991; Merrick 1975; Miller 1979; Nelson and
Kimengich 1984) and both LSA and MSA
occupations have been identified. The LSA
in East Africa dates between about 40,000
B.P. and 1000 B.P. (Robertshaw 1995), and
much of this time is sampled at Lukenya
Hill. All of the LSA lithic assemblages at Lukenya Hill are microlithic, but those dating
earlier than about 21,000 B.P. lack geometrics and the backed blades tend to be large.
After 21,000 B.P. geometric microliths,
backed blades, outils écaillé, and a standardized end scraper (fan scraper) become common. This sequence is similar to others in
East Africa where the predominant raw material is a poor quality quartz or other intractable raw material. No formal names exist
for these LSA assemblages, but I have divided them into three basic groups based
on major technological features, following J.
Deacon’s (1984) recommendations: Late
Pleistocene Non-Geometric (40,000 to about
22,000 B.P.), Late Pleistocene Geometric
(broadly equivalent to the period including
the Last Glacial Maximum; 22,000 to 10,000
B.P.), and Holocene Aceramic (10,000 to
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roughly 5000 B.P.). MSA assemblages are
present but undated.
I have studied four Lukenya Hill sites
where faunal assemblages produced by
hunter – gatherers are preserved. Other sites
either lack faunal assemblages, have very
small ones, or are clearly pastoral occupations. Site GvJm19 is a rock overhang that
forms a small sheltered area. Three archaeological components are present: a Late Pleistocene Geometric, a Holocene Aceramic in
the early Holocene, and a middle Holocene
assemblage with ceramics and domestic animals. GvJm22 is a rockshelter with two major components: a Late Pleistocene Geometric that dates to the Last Glacial Maximum,
separated by a disconformity from a late Holocene occupation with ceramics and domestic fauna. GvJm46 is an extremely large
open-air site sampled by eleven 1-m2 pits.
About 30 – 50 cm below the surface begins a
dense Late Pleistocene Geometric occupation that varies between 30 cm to 1 m thick,
much of which dates to the Last Glacial Maximum and perhaps earlier. Faunal and artifactual material is nearly absent at 170 cm
below the surface where a thin lag deposit
of eroded rock is found. Below 170 cm is a
dense MSA occupation. GvJm62 is a small
open-air site with three components: a Late
Pleistocene Non-Geometric, a Late Pleistocene Geometric, and a Holocene pastoral occupation at the top. Excavation details, radiocarbon dates, and artifactual descriptions
for these four sites can be found elsewhere
(Barut 1994; Bower et al. 1977; Bower and
Nelson 1978; Gramly 1976; Gramly and
Rightmire 1973; Marean 1990, 1992b; Marean
and Gifford-Gonzalez 1991; Merrick 1975;
Miller 1979; Nelson and Kimengich 1984).
The best sampled time unit is the period between 20,000 and 12,000 years BP; GvJm19,
GvJm22, GvJm46, and GvJm62 all have occupations dating to that time, and all four
sites are within several hundred meters of
each other (see Fig. 7).
A wide range of zooarchaeological evi-
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FIG. 7. Map showing a close-up of Lukenya Hill and the location of the four Lukenya Hill sites
discussed in the text.
dence bears on the models of grassland adaptations, including species richness, mortality profiles, and skeletal element representation. I have described the Lukenya Hill
zooarchaeological and taphonomic data
elsewhere (Marean 1990, 1991, 1992b; Marean and Gifford-Gonzalez 1991), so I will
briefly review the pertinent interpretations
here. None of the Lukenya Hill sites show
much evidence for carnivore involvement as
either accumulators or ravagers. This is
shown by the low frequency of carnivore
tooth marks and the lack of carnivores in the
assemblages. Rodents (such as porcupines)
are also weakly and inconsequentially implicated in the taphonomic history of the assemblages as documented by the low frequencies of rodent gnawing. Together with
the abundance of stone tool cut marks and
hammerstone percussion marks on the
bones, and the abundant lithic artifacts, the
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data suggest that people were the primary
accumulators of these assemblages.
Taphonomic processes differentially affected the preservation of bones from these
sites. The two sites with the largest samples,
and thus the most useful for examining skeletal element abundance, differ significantly
in bone survival. The fauna from GvJm46
suffered severe destruction after hominid
discard by abiotic processes. Few shaft fragments were longer than 2 cm, and only the
most dense portions of bone survived. A
completeness index developed to measure
postdepositional destruction documents extraordinary breakage due to abiotic processes at GvJm46 (Marean 1991). GvJm22
suffered much less postdepositional destruction. The most prudent conclusion is
that the skeletal element representation at
these two sites cannot be usefully compared,
while GvJm19 and GvJm62 have skeletal ele-
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ment sample sizes too small to be analytically useful. For this reason I will focus my
attention on species representation and mortality profiles, and exclude a discussion of
skeletal element representation.
Species Richness
The raw data on species recognition and
representation at Lukenya Hill have been reported elsewhere (Marean 1990, 1992b; Marean and Gifford-Gonzalez 1991). The most
abundant large mammal in the MSA and
Late Pleistocene LSA deposits at Lukenya
Hill is an extinct small alcelaphine antelope.
This alcelaphine was smaller than any extant
East African alcelaphine, but similar in body
size to the modern bontebok/blesbok (Damaliscus dorcas) found in southern Africa.
The extinct alcelaphine had an extremely
high hypsodonty index, suggesting an abrasive diet. I have not assigned it to a precise
extant taxon nor named a new species as the
material is simply not diagnostic enough to
warrant a specific assignation.
Other taxa that are well represented in the
undated MSA and Late Pleistocene LSA deposits include species currently abundant on
the Athi-Kapiti Plains, such as Thomson’s
gazelle, wildebeest, burchell’s zebra, and
warthog. Many other extant species are also
represented but in small numbers. Several
other rare but notable occurrences include
the extinct giant buffalo Pelorovis antiquus,
and two species that are currently not found
in the region: Grevy’s zebra (Equus grevi)
and oryx (Hippotragus oryx). The faunal representations suggest both similarities with
and departures from the modern system.
Some features present today in the AthiKapiti Plains were clearly also characteristic
of the past: bush habitat was present on and
immediately beside the inselberg, and the
Athi-Kapiti Plains were predominantly
grasslands. The presence of species specialized to dry grass feeding, such as Grevy’s
zebra and oryx, suggests that the sur-
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rounding grasslands may have been more
arid for longer periods of the year than is
the case today. This would account for the
rareness of the wildebeest, a moist grass
feeder, and the greater abundance of the extinct alcelaphine, a possible dry grass specialist (Marean 1992b). Alternatively, the
lack of wildebeest and abundance of the extinct alcelaphine may reflect differences in
their migration patterns and how these correlated with the scheduling of visits to the
inselberg by hunter – gatherers.
Figure 8 shows the species richness for
all Lukenya Hill hunter – gatherer occupations plotted against sample size. It is well
known that species richness increases as a
function of sample size, and this relation is
typically a logarithmic function (Grayson
1984). Plotting species richness against
sample size allows one to compare richness values of similar sample size visually,
but also facilitates empirical corrections to
the sample size affect with an analysis of
standardized residuals (Rhode 1988, Jones
et al. 1983). Clearly, as sample size in the
Lukenya Hill assemblages increases, so
does richness. The overall correlation,
however, is insignificant (r Å .51, p ú .05)
due to the presence of two distinct linear
relationships. One relationship, composed
of most of the sites, displays a greater intercept with a similar slope. The second
relationship, composed of the two GvJm46
occupations plus the small Holocene sample at GvJm62, displays a lower intercept.
Both occupations at GvJm46 clearly show
much lower species richness than other
sites of comparable sample size, and remains of the extinct small alcelaphine comprise all but a small fraction of the sample.
GvJm62 is dominated by domestic cattle.
To summarize, the LSA and MSA occupation at GvJm46 are unique at Lukenya Hill
in that they have large sample sizes and very
low species richness. GvJm62 also has low
species richness but the sample size is very
small and it is clearly a pastoral occupation.
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FIG. 8. The log of species richness (number of taxa) versus the log of sample size for the Lukenya
Hill sites. Rockshelters are shown as circles, open-air sites are shown as triangles.
The Late Pleistocene LSA occupations at
GvJm19, GvJm22, and GvJm46 all are
roughly contemporaneous and date to the
Last Glacial Maximum, have similar sample
sizes, and are close together. However, they
differ in that the rockshelters (GvJm19 and
GvJm22) are species rich while the open-air
occupations (GvJm46) are species poor. We
can conclude that the GvJm46 occupations
show a specialized species representation
that reflects a focus on one species to the
exclusion of the other species that were
clearly present, as documented at GvJm19
and GvJm22.
Mortality Profiles
Mortality profiles are graphical representations of estimates of the age-at-death of
fossil taxa. Three basic mortality models are
current. The catastrophic model (Klein and
Cruz-Uribe 1984), or life-structure model
(Stiner 1990), has a frequency of age groups
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resembling a living population. A profile
where very young and very old individuals
surpass other age classes is called the attritional model (Klein and Cruz-Uribe 1984),
or U-shaped model (Stiner 1990). The third
model, the prime-dominated model, has a
dominance of prime-age adults (Stiner
1990). These models all assume that the mortality profile preserved in an archaeological
site closely resembles the age representations of prey killed by people in the past.
Mortality profile analysis has grown increasingly sophisticated in its theory addressing the ecological meaning of the profiles. However, theory that relates to the
formation of mortality profiles in the archaeological record is less robust. More simply
put, we do not know how closely the profile
we generate from archaeological sites, what
I will call the archaeological profile (Fig. 9),
resembles the actual mortality profile of
prey species as killed by the people in the
past (the death profile). It is typically the death
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profile we wish to reconstruct. The two main
processes that stand between the archaeological profile and the death profile are differential destruction of teeth, and differential transport of heads of different size/age
prey.
Klein and Cruz-Uribe (1984) have argued,
due to the less dense and fragile nature of
deciduous dentitions compared with adult
dentitions, that the archaeological profile is
likely to be biased against juvenile individuals still without adult dentitions. These are
juveniles typically in the first 10% age interval. Thus our estimates of the relative representation of juveniles will nearly always be
underestimates, and the relative representation of these individuals will vary widely as
a function of the extent of destructive processes. Heavily comminuted assemblages,
such as GvJm46, will have a greater loss of
juveniles compared with adults than a less
comminuted assemblage, such as GvJm22.
This means that the discarded profile (the profile discarded at the site by the occupants)
will differ from the archaeological profile. I
have argued that a check can be made on
this loss by estimating the number of juveniles from bone fusion and comparing that
to the dentition-generated mortality profile
(Marean 1995). Unfused bones are less dense
than fused bones (Brain 1981) so this is not
a perfect test; however, it does provide a
second estimate of the number of juveniles
present.
The problem of differential transport is
potentially more manageable. A wide range
of ethnoarchaeological studies has shown
that many contingencies affect hunter – gatherer transport of carcass parts (Binford 1981;
Bunn et al. 1988; O’Connell and Hawkes
1988; O’Connell et al. 1989). Several basic
patterns have emerged from these studies.
Other contingencies being equal, hunter –
gatherers transport smaller mammals more
completely than larger mammals. The significance for mortality studies is that animals may pass through several body size
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categories on their way to adulthood. Any
animal in the size 3 category (which, as defined by Brain 1981, includes red deer, caribou, reindeer, wildebeest, hartebeest, and
many others) begin their lives in size 1 with
deciduous teeth, pass through size 2, and
end up in size 3 with a fully adult dentition.
Thus zooarchaeologists should anticipate
that decisions for the transport of heads
should vary as the animal ages, and the
shape of the mortality profile will be sensitive to these decisions. The data on body
part transport by Hadza hunter – gatherers
shows that the heads of size 2 animals are
transported more often than the heads of
size 3 animals (Bunn et al. 1988, O’Connell
and Hawkes 1988, O’Connell et al. 1989).
A second pattern is that, other contingencies being equal, large groups of people
transport animals more completely than
small groups of people. This observation is
particularly problematic for researchers attempting to compare mortality profiles between sites that sample different settlement
systems. For example, if one settlement system was occupied on average by large
groups of people, then the residential base
may have a more comprehensive mortality
profile because the large group of people can
reduce transport bias for large animals. A
settlement system occupied on average by
a small group of people may show greater
selectivity of large heads, thus biasing
against older animals at the residential sites.
Hunter – gatherers also transport animals
more completely the shorter the distance to
be transported. Thus if the encounter site
(the place where an animal was killed or
scavenged) is close to the residential camp
there may be less bias in the archaeological
mortality profile than if the encounter site is
far from the residential site.
This means that the transported profile (the
sample of heads transported from encounter
sites to residential sites) may differ from the
death profile. Importantly, the transported profile may or may not differ from the encounter-
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FIG. 9. Flowchart showing the taphonomic stages of alteration that mortality profiles pass through
before interpretation by the archaeologist. This set of stages is equally applicable to skeletal element
profiles, as recognized by many researchers.
point profile (that sample of heads discarded
at the encounter site). Figure 9 illustrates
these points. One way to attempt to account
for these problems is for zooarchaeologists
to sample the mortality profiles from various
site types within a hunter – gatherer settlement system. By sampling prey encounter
sites and residential sites, we can control for
the varying transport behaviors that were in
operation. This is at least partially possible
with the Last Glacial Maximum occupations
at GvJm22 and GvJm46, because, as I will
discuss later, GvJm22 is a residential site and
GvJm46 is a kill site.
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Figure 10 shows the mortality profiles for
the extinct alcelaphine from GvJm22 and
GvJm46 plotted as a histogram and Fig. 11
shows the age profiles plotted as a ternary
diagram with the three models illustrated
following Stiner (1990). All three mortality
profiles show a dominance by the first and
second adult age classes (prime-age adults)
and the frequency of individuals declines
rapidly after that. All three profiles would
classify as ‘‘prime-dominated profiles’’ following Stiner’s criteria, and all are statistically indistinguishable (Kolmogorov – Smirnov Test, p ú .05).
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shown by the dentitions. Including these juveniles makes the profile look much more
similar to a ‘‘catastrophic profile.’’ It is possible that even more juveniles were originally
present than recorded by the preserved unfused bones.
If the GvJm22 and GvJm46 mortality profiles are sampling the same population of
hunted antelope then we would expect that
the seasonal signatures between the two
sites would be similar. It is not possible to
estimate season of death with cementum increments from the Lukenya Hill dentitions
because the teeth are nearly all isolated and
weathered. If there is a strong seasonal signal to the killing identifying seasonally sensitive peaks and troughs in crown heights
may be possible. Figure 12 shows the incidence of adult teeth in metric units equal to
about two months of growth for GvJm22
and GvJm46. Both sites show a weak tendency to have synchronous peaks of abundance at 12-month intervals, but the small
sample sizes certainly warrant caution in the
interpretation of these data.
FIG. 10. Frequency histograms showing the mortality
profiles with the ages broken into 10% increments of
the estimated ecological longevity of the extinct small
alcelaphine. The thick bars show the number of individuals by teeth, and the thinner black line on top of the
bars shows the correction provided by bones.
As I noted earlier, most mortality profiles
will be biased against younger individuals
due to the greater susceptibility of deciduous dentitions to destruction. Each of the
mortality profiles shows a correction of the
mortality profile derived from the bone fusion data. These corrections are taken from
early fusing unfused bones. As we do not
have fusion tables for the extinct alcelaphine, I have used ages from goats, which
are roughly the same body size as the extinct
alcelaphine. The bones show that many
more juveniles are represented than are
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DISCUSSION
The Last Glacial Maximum occupations at
GvJm19, GvJm22, GvJm46, and GvJm62 show
interesting patterns of similarity and contrast.
Given the close proximity of the sites and the
overlapping dates of occupation, it is likely
that these sites were used as parts of the same
settlement system. Several lines of evidence
suggest that GvJm19 and GvJm22 were residential sites in this settlement system: (1) the
abundance of lithic artifacts, (2) the presence
of hearths and burnt bone, (3) the rockshelter
location, and (4) the high species richness of
the fauna sampling several nearby habitats.
Despite a diversity of animals, the small extinct alcelaphine was clearly the preferred
prey animal at GvJm22, while hartebeest was
the preferred prey at GvJm19. This could potentially represent a difference in the seasons
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FIG. 11. Ternary diagram showing the mortality profile models as defined by Stiner (1990), the
position of the extinct small alcelaphine from GvJm22 LSA (black circle), GvJm46 LSA (open star), and
GvJm46 MSA (black star) without correction by including bones (above) and with correction by including
bones (below).
of occupation, though we currently have no
data to test this idea.
GvJm46 has a different topographic context than the other sites. GvJm46 is on a slope
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at the base of a steep cliff (Fig. 7). No natural
shelter exists over the site, so it is directly
exposed to sun, rain, and wind nearly the
entire day. GvJm46 is a very large site
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FIG. 12. The frequency of the extinct small alcelaphine by 2 month age increment (estimated metrically
from crown height) in the LSA of GvJm22 and GvJm46.
The lines connecting the two graphs are placed at 12month intervals.
though the exact dimensions are not yet documented. The 11 excavated pits sample only
a fraction of the deposit, suggesting that the
unexcavated assemblage is immense and
vast numbers of this small alcelaphine antelope likely remain unexcavated. A ravine
formed by a seasonal stream runs to the
north of the site, starting at the inselberg
and running southwest onto the plains. This
ravine is shrouded by a gallery forest in an
otherwise grassland habitat. The wooded ravine and the long cliff face form a natural
box with the site of GvJm46 within. As Fig.
7 shows, the migration of animals is split
by Lukenya Hill, and the right split passes
directly through the bottleneck formed by
Lukenya Hill and the Mua Hills to the east.
It is this excellent hunting location that likely
accounts for the density of sites on the eastern face of Lukenya Hill.
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Several lines of evidence converge to suggest that GvJm46 was a mass-kill site where
the small extinct alcelaphine antelope was
repeatedly killed in Late Pleistocene LSA
and MSA times: (1) the open location in a
natural topographic trap situated in a bottleneck along a well-documented migration
route, (2) the concentration of one species of
grassland antelope compared to high diversities of large ungulates at contemporary
nearby residential sites, (3) the catastrophic/
life-structure mortality profile, and (4) the
likelihood that GvJm46 represents many different kill events. If the site were formed
by just a few kills, the volume of animals
necessary to account for the kill, including
the unexcavated material, would be enormous. Animals were probably driven between the wooded ravine and the cliff face
as they migrated north, and if the ethnographic literature is any guide, placing people in the wooded ravine to keep animals
from escaping the trap would have been effective. The landscape may even have been
modified, though no obvious evidence survives to attest to that possibility. Alternatively, it is possible that animals were driven
off the cliff above onto the slope, though I
think this is less likely.
The mortality profiles from GvJm46
closely resemble the catastrophic/life-structure model, and this is the anticipated profile
shape when a mass kill of animals has occurred. However, it is important to note that
there is very little taphonomic data to support this assumption. The mortality profiles
from GvJm22 and GvJm46 are visually similar and statistically indistinguishable. Above
it was argued that mortality profiles will be
affected by differential transport decisions
that in turn are affected by distance between
the encounter site and the residential site,
number of people available for transport,
and size of the animal. If differential transport were occurring, then mortality profiles
from transported assemblages (GvJm22) and
encounter assemblages (GvJm46) should
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differ. The close similarity between GvJm22
and GvJm46 suggests that differential transport was not occurring, assuming these sites
were part of the same settlement system.
This is not surprising, however, because the
distance between these two sites is only several minutes walk and the animal being
transported not particularly large.
When the evidence from GvJm19, GvJm22,
GvJm46, and GvJm62 is considered together,
the Seasonal Grassland Model best describes
the exploitation of the Athi-Kapiti Plains
during the Last Glacial Maximum. It posits
a seasonally shifting strategy where tactical
landscape use is employed during seasons
when migrations or aggregations of mammals result in a situation conducive to mass
killing. GvJm46, as showed by its low species richness, catastrophic mortality profile,
and topographic location, is best explained
as a tactical kill site. The Seasonal Grassland
Model posits that during other seasons of
the year hunters will switch back to a generalized strategy of killing a diversity of large
mammals and collecting more plant foods.
GvJm19 and GvJm22 represent residential
sites where this greater species richness of
prey animals is represented. I argued earlier
that the Seasonal Grassland Model was unlikely to apply to tropical African grasslands. Thus, the Late Pleistocene evidence
from Lukenya Hill is inconsistent with my
original predictions.
Though there currently is no excavated
MSA rockshelter site at Lukenya Hill with
an informative faunal assemblage, the close
similarity between the MSA and LSA occupations at GvJm46 suggest similar interpretations for these occupations. This indicates
that as early as the MSA, people on the AthiKapiti Plains were using tactical techniques,
and probably the communal hunting strategies necessary to make tactical techniques
function. Thus, the GvJm46 occurrence is, so
far, the only MSA site in Africa where tactical techniques are directly implicated,
though Klein has argued, from the evidence
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at several cave assemblages, that MSA hunters in South Africa killed eland with tactical
techniques (Klein 1989). Several Middle Paleolithic sites in Western Europe also display
evidence of tactical hunting (Coudoulous,
La Borde, Mauran, Le Roc; see discussion
in Mellars 1996) and the Mousterian record
from the Caucasus may also have evidence
of tactical hunting (Hoffecker et al. 1991;
Baryshnikov and Hoffecker 1994). These
data suggest that Middle Paleolithic/Middle
Stone Age hunters in Europe and Africa
were capable of highly organized hunting
behavior.
The Holocene occupations at GvJm19 and
GvJm62 are much less informative due to
the small samples and the lack of site variety. The early Holocene occupation at
GvJm19 shows a species rich fauna similar
to the Last Glacial Maximum levels of
GvJm19 and GvJm22. This is surprising as
East Africa was colder and drier during the
Last Glacial Maximum and warmer and
wetter during the early Holocene (Hamilton
1982). Given these differences we would anticipate a richer fauna in the early Holocene,
but this is not documented at Lukenya Hill.
The Holocene sites represented at Lukenya Hill show species rich faunas that are
most consistent with the Generalized Grassland Model. There is no evidence for the
presence of a Holocene mass-kill site at
GvJm46, nor anywhere else at Lukenya Hill.
This could be a sampling problem. There is
no other Holocene locality in East Africa,
however, that resembles a mass-kill locality
despite many excavations at numerous sites
in diverse regions.
In the earlier discussion it was argued that
East African grasslands are sufficiently rich
in plant foods and resident animals that
risky time-intensive strategies such as tactical landscape use simply are not needed. If
the Seasonal Grassland Model was employed as a hunting strategy during the Late
Pleistocene, then either something is amiss
with the models and the ecological parame-
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TROPICAL GRASSLAND HUNTER – GATHERERS
ters as I have defined them, or the relevant
ecology differed sufficiently from the present state in the Late Pleistocene of Africa as
to make the Seasonal Grassland Model the
favored hunting strategy. The lack of evidence for tactical landscape use in the ethnographic record, and in the Holocene archaeological record, argues against the former.
However, paleoenvironmental data from
East Africa suggests that ecological conditions were, indeed, much different during
the Last Glacial Maximum.
The Last Glacial Maximum climate in East
Africa was roughly 5 to 7 degrees centigrade
colder than present as shown by the placement of glacial moraines on several East African mountains (Osmaston 1989a, 1989b).
It is not yet known how this temperature
difference was distributed by season. Rainfall in the wooded areas of East Africa was
less as indicated by the general lowering of
lake levels, increase in grass pollen, and
changes in vegetation zones on mountains
(Hamilton 1982). Paleolimnological evidence suggests that rainfall may have been
more seasonal during the Last Glacial Maximum (Richardson and Richardson 1972), occurring in one season as opposed to two, and
it is possible that some grassland ecosystems
received similar levels of rain as today but
more tightly restricted in time. The cooler
temperatures would also have lowered
evapotranspiration rates, keeping grasses
moist and green longer after the rains.
These different climatic conditions may
have lowered the return rates during the
Late Pleistocene for several classes of food
items compared with the Holocene. More
seasonal rainfall and lowered temperatures
are likely to have lowered the species richness and density of AGPs, thus increasing
search costs and making them more susceptible to patch depletion. USOs would also
have been less diverse and dense in cooler
grasslands (see the discussion above), so it
is likely that search costs were higher and
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return rates were lower for USOs during the
Last Glacial Maximum.
Large mammal biomass in Africa correlates
positively with rainfall (Coe et al. 1976), and
thus if rainfall were less during the Last Glacial Maximum then resident mammals would
likely have been less diverse, more widely
spaced, and less abundant due to the lowered
forage quality of the vegetation. This would
have increased the search costs for resident
mammals and made them more susceptible
to patch depletion. Migratory mammals may
have been less abundant and less diverse due
to the lowered rainfall and lowered forage
quality. When these animals are closely
packed into a mobile patch during a migration, however, it is likely that search costs
would not change dramatically because the
animals would still be passing by in large
numbers. Also, it is unlikely that even intensive stone age hunting strategies would deplete migratory herds to the point that return
rates would be significantly decreased during
the period that a herd was being preyed upon
(see discussion in Kelly 1995).
The grasslands of East Africa during the
Last Glacial Maximum may have been transformed in the direction of temperate grasslands with less diverse and less dense plant
foods and greater seasonality of all food items.
The lowered species richness, lowered density, and increased seasonality of these resources may have made tactical landscape
strategies a more effective strategy, just as they
were in temperate grasslands.
CONCLUSIONS
Cold, temperate, and tropical grasslands
are similar in important ways: water and
raw materials are often scarce, rainfall is
highly seasonal, the most abundant mammals are large gregarious and mobile herbivores. Tropical grasslands differ in some important ecological parameters that should
affect hunter – gatherer foraging strategies.
For example, in the tropics there is a greater
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CURTIS W. MAREAN
species richness and biomass of edible AGPs
and USOs making carbohydrate more
readily availability and less seasonal in
availability. Large mobile mammals are
more diverse and have greater biomass and
the migrations are characterized by a succession of complementary feeders. Resident
large mammals are also more diverse and
have greater biomass. Overall, tropical
grasslands are a richer and less temporally
punctuated environment than either cold or
temperate grasslands.
These ecological parameters led to the
construction of three models for hunter –
gatherer exploitation of tropical grasslands.
The model deemed most likely for East African grasslands was the Generalized Grassland Model. In a preliminary test of these
models the Holocene archaeological evidence is most consistent with the Generalized Grassland Model. The archaeological
evidence dating to the Last Glacial Maximum on the Athi-Kapiti Plains is most consistent with the Seasonal Grassland Model.
These differences in hunting strategies were
probably due to the different ecological conditions of the Last Glacial Maximum that
made the East African grasslands more similar to temperate grasslands in several ecological parameters.
ACKNOWLEDGMENTS
This paper benefited from the helpful comments of
David J. Bernstein, Robert J. Blumenschine, John R. F.
Bower, Jeanne Sept (referee), John J. Shea, and an anonymous referee. I thank the Office of the President of the
Republic of Kenya for permission to conduct research
in Kenya, and the National Museums of Kenya for providing facilities and for access to the archaeological and
comparative materials. This research was funded by
grants to Marean by the following: Boise Fund, L.S.B.
Leakey Foundation, National Science Foundation (BNS8815128), and Sigma Xi.
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