Evidence for declines in human population densities
during the early Upper Paleolithic in western Europe
Eugène Morin*
Department of Anthropology, Trent University, Peterborough, ON, Canada K9J 7B8; and Centre Interuniversitaire d’Études sur les Lettres, les Arts et les
Traditions (CELAT), Département d’Histoire, Laval University, Québec, QC, Canada G1K 7P4
Communicated by Erik Trinkaus, Washington University, St. Louis, MO, October 2, 2007 (received for review July 19, 2007)
In western Europe, the Middle to Upper Paleolithic (M/UP) transition, dated between ⬇35,000 and ⬇40,000 radiocarbon years,
corresponded to a period of major human biological and cultural
changes. However, information on human population densities is
scarce for that period. New faunal data from the high-resolution
record of Saint-Césaire, France, indicate an episode of significant
climatic deterioration during the early Upper Paleolithic (EUP),
which also was associated with a reduction in mammalian species
diversity. High correlations between ethnographic data and mammalian species diversity suggest that this shift decreased human
population densities. Reliance on reindeer (Rangifer tarandus), a
highly fluctuating resource, would also have promoted declines in
human population densities. These data suggest that the EUP
represented for humans a period of significant niche contraction in
western Europe. In this context, the possibility that a modern
human expansion occurred in this region seems low. Instead, it is
suggested that population bottlenecks, genetic drift, and gene
flow prevailed over human population replacement as mechanisms
of evolution in humans during the EUP.
archaeology 兩 Rangifer 兩 Middle to Upper Paleolithic transition 兩
modern human origins 兩 Neandertals
I
n western Europe, significant changes occurred during the Middle
to Upper Paleolithic (M/UP) transition, including a widespread
adoption of blade-based toolkits, the emergence of artistic behavior, and a shift toward modern human anatomical features. Focusing on population size and density, two key aspects of human
evolution (1) might help in understanding the nature of some of
these changes. However, little is known about population dynamics
of human foragers before the Holocene (2, 3). Because forager
density seems to be affected by climate (4), investigating the impact
of climate change on human demography may yield insights into the
evolution of human populations during the M/UP transition.
Ethnographically, human forager densities were particularly low
in high latitudes, a pattern attributed to low plant and mammal
species diversity and high fluctuations in ungulate productivity (4,
5). Human densities generally were higher in more temperate
environments where mammal species are more diverse (6). In this
article, the potential relationship between terrestrial mammal species diversity and human population density is scrutinized. The
correlations obtained then are used to investigate the demographic
implications for human groups of shifts in terrestrial mammal
species diversity in the M/UP transition record. However, it should
be noted that species diversity is only one of many possible
parameters affecting human populations. Nevertheless, this parameter seems to provide a useful proxy for assessing changes in human
densities.
Ecologists have long noted that species diversity of terrestrial
mammals decreases with latitude and tends to be highest in the
tropics, intermediate in temperate habitats, and lowest in the Arctic
(7). Most of the changes in latitudinal gradients would be explained
by correlates of temperature (e.g., annual minimum temperature,
frost-free season length), moisture (e.g., evapotranspiration), and
elevation (8, 9). Temporally, shifts in local climatic conditions can
48 –53 兩 PNAS 兩 January 8, 2008 兩 vol. 105 兩 no. 1
have effects similar to latitudinal gradients by increasing or decreasing species diversity (10).
In western Europe, Middle Paleolithic and early Upper Paleolithic (EUP) foragers depended mostly on terrestrial mammals for
subsistence, particularly moderate (goat-sized) to large (bisonsized) ungulates. Marine mammals and lacustrine resources seem to
have played a marginal role in the diet of these human populations
(11) and, as a result, are not considered further here. North of the
Pyrenees and the Alps, archaeofaunas dated to the M/UP transition
generally are dominated by five species: aurochs (Bos primigenius),
steppe bison (Bison priscus), horse (Equus caballus), red deer
(Cervus elaphus), and reindeer (Rangifer tarandus). Paleoenvironmental reconstructions suggest that aurochs and red deer were most
abundant in temperate woodlands and grasslands, whereas steppe
bison and horses preferred temperate and cold steppe ecosystems
(12). Today, these biomes are, by European standards, moderately
rich in species (9). In contrast, reindeer would have been strongly
associated with the boreal forest and the arctic tundra (12), two
biomes with low species diversity. Therefore, temporal changes in
the relative abundance of ungulate species may signal shifts in range
occupancy and an associated reduction in species diversity that
might have affected human populations. Here, ethnographic and
wildlife data are used to predict how variations in terrestrial
mammal species diversity may affect human population densities.
These findings then are applied to the faunal sequence from
Saint-Césaire, a M/UP transitional site in western France.
Mammalian Species Diversity Versus Forager Densities
Density data were compiled for 27 ethnographically documented
forager populations from North America and compared with the
total number of terrestrial mammalian species present historically
within their respective territories (Table 1). Only Plains, Subarctic,
and Arctic foragers were incorporated into the sample, to enhance
comparability with Late Pleistocene ecosystems of western Europe
(for a fuller discussion of the samples, see Materials and Methods).
A positive correlation (rs ⫽ 0.62, P ⬍ 0.002) was found between
forager density and mammalian species diversity in North America
(Fig. 1). However, six human groups from cold, open country
ecosystems seem to belong to a cluster distinct from the one formed
by 21 forested northern and temperate grassland groups. The
reason for this separation is not clear, but it may have to do with a
latitudinal gradient in ungulate patchiness in open versus forested
environments. Considering these two data sets separately increases
the correlations (forested northern and temperate grassland
groups: rs ⫽ 0.82, P ⬍ 0.001; cold, open country groups: rs ⫽ 0.81,
P ⬍ 0.07). Importantly, the same relationship is found in both
clusters: population densities decline with decreasing diversity of
terrestrial mammalian species. Although these correlations do not
provide proof of causality—they simply may reflect an underlying
Author contributions: E.M. designed research, performed research, analyzed data, and
wrote the paper.
The authors declare no conflict of interest.
*To whom correspondence should be addressed at: Department of Anthropology, Trent
University, Peterborough, ON, Canada K9J 7B8. E-mail: [email protected].
© 2008 by The National Academy of Sciences of the USA
www.pnas.org兾cgi兾doi兾10.1073兾pnas.0709372104
Table 1. Human densities and diversity of native mammalian species associated with 27 hunter– gatherer groups from North America
Area
Arctic
Subarctic
Plains
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
Group
Density,
n/100 km2
Species
diversity
Location
Latitude N
Longitude W
Mountain people
Asiaqmiut
Patliqmiut
Naskapi
Chipewyan
Attawapiskat Cree
Dogrib
Hare
Kolchan
Slave
Nabesna
Sekani
Yellowknife
Grand Lake Victoria Cree
Tahltan
Beaver
Waswanipi Cree
Micmac
Blackfoot
Plains Cree
Assiniboine
Crow
Arapaho
Cheyenne
Kiowa-Apache
Comanche
Kiowa
1.4
1.0
1.3
0.4
0.4
1.4
0.6
0.5
0.5
1.4
0.6
1.0
0.2
0.7
1.1
0.5
0.5
2.3
4.3
1.9
5.8
2.6
3.0
3.0
1.4
5.0
1.4
29
18
18
29
31
34
31
27
34
39
35
46
23
41
46
45
37
40
40
46
44
60
76
66
48
52
57
Alaska
Nunavut
Nunavut
Québec
Manitoba
Ontario
NW Territories
NW Territories
Alaska
NW Territories
Alaska
British Columbia
NW Territories
Québec
British Columbia
Alberta
Québec
New Brunswick
Alberta
Saskatchewan
Saskatchewan
Montana
Colorado
Wyoming
Oklahoma
Texas
Oklahoma
67°30⬘
62°
62°
54°
60°
52°30⬘
64°
66°45⬘
62°30⬘
60°30⬘
62°30⬘
56°30⬘
64°15⬘
48°30⬘
57°30⬘
57°15⬘
49°30⬘
47°
51°
52°
50°
45°
40°
42°30⬘
36°
33°
36°30⬘
154°45⬘
99°45⬘
95°
69°
99°45⬘
83°30⬘
116°
126°
154°30⬘
120°
141°
125°15⬘
111°45⬘
77°45⬘
130°
119°
76°30⬘
66°30⬘
112°30⬘
107°
105°
108°
105°
105°30⬘
99°
100°
102°
Density data from Kelly (6) and Burch (5). The mid-value was adopted for Dogrib density. Numbers of native mammalian taxa were compiled by using the
interactive maps of the Smithsonian Museum of Natural History web site on North American mammals (www.mnh.si.edu/mna//main.cfm). Coordinates
corresponding to the center of the historical range occupied by each hunter– gatherer group were used to calculate species diversity as assessed based on maps
in Sturtevant (46). Except for bison (added to the species list for nos. 16 and 19 –27), no attempt was made to correct for recent changes in species distribution.
Hunter-Gatherer Density (n/100 km2)
10
1
0.1
10
100
Mammalian Species Diversity (n species)
Fig. 1.
Relationship between hunter– gatherer density and mammalian
species diversity (log-log scale). Triangles are cold, open-country human
groups (Table 1, nos. 1–3 and 19 –21), and solid circles are forested northern
and temperate grassland human groups (Table 1, nos. 4 –18 and 22–27).
Morin
similarity of the compared ecosystems, it is reasonable to assume
that shifts in terrestrial mammalian species diversity during the
M/UP transition in western Europe would have been accompanied
by changes in human population densities.
Rangifer Fluctuations in Abundance and Human Demography
Historically, humans that were heavily dependent on wild Rangifer
had low population densities and appear to have experienced
demographic fluctuations of higher amplitude compared with
populations with more diverse diets (4, 5).
The tendency of Rangifer populations to experience sporadic
fluctuations of abundance, sometimes with rough patterns of
periodicity, is known (13). For example, after a peak at the end of
the 19th century, the George River herd (Québec, Canada) declined dramatically in the early 20th century and remained low until
the 1960s, when it was estimated at ⬇4,700 individuals and considered on the verge of extinction. Yet this population reached a
new estimated peak of ⬇776,000 caribou in 1993. In 2001, the
estimate had fallen to ⬇385,000 caribou, suggesting that the population had entered a new declining phase (14, 15). In this case, the
amplitude of the fluctuation is 165:1.
Fluctuations of Rangifer abundance are extremely variable, with
durations between highs and lows ranging from only decades to
slightly more than a century. Some Rangifer populations in southwestern Alaska exhibit a 40- to 50-year periodicity (16), whereas in
Greenland some Rangifer populations have a periodicity of 65–115
years (17). Peary caribou in the Canadian High Arctic have
exhibited a relatively short 20-year periodicity (18). These fluctuations in abundance have been observed in the absence of human
and carnivore predation and most commonly are attributed to
PNAS 兩 January 8, 2008 兩 vol. 105 兩 no. 1 兩 49
ANTHROPOLOGY
relationship driven by an as-yet-unidentified parameter (e.g., total
animal biomass or total ungulate biomass)—they suggest that
mammalian species diversity can be used to predict forager density,
an approach compatible with the critical role played by terrestrial
mammals in the diet of these human groups. As a result of the
210
140
70
Mulchatna
0
75
Nelchina
Alaska
50
25
0
Fortymile
40
20
0
Numbers of caribou (in thousands)
750
George River
500
250
QuébecLabrador
0
Feuilles River
500
250
0
1.6
Nuuk
0.8
Greenland
0
8.0
Sisimiut
4.0
0
600
Taimyr
400
200
0
75
Lena-Olenek (Bulunsk)
Russia
50
25
0
100
Yana-Indigirka
50
0
2
85
-1
48
18
7
87
-1
73
8
1
2
90
-1
98
8
1
7
92
-1
23
19
2
95
-1
48
9
1
7
97
-1
73
9
1
2
00
-2
98
9
1
Fig. 2. Temporal fluctuations of Rangifer populations in four regions: Alaska (data from refs. 16, 47, and 48), Québec-Labrador (data from refs. 14, 15, and
49), western Greenland (data from ref. 17), and northern Russia [data from refs. 21 (pp. 44 and 66) and 50 (pp. 79 – 83)]. All values connected by a solid line are
based on surveys, except for Greenland (caribou skin trade counts before 1950, caribou kills after 1950). Values connected by a dashed line are extrapolations
based on historical data. The 1935 value (500,000) for the Fortymile herd was not included here because it is probably an overestimation. When multiple values
were available for a specific time interval, the one nearest to the middle of the interval was adopted.
overgrazing or to extremely unfavorable snow and ice conditions
(13, 19).
Another characteristic of several, but not all, Rangifer populations is that their lows tend to be synchronized at a regional scale,
a phenomenon possibly mediated by large-scale climate systems
such as the North Atlantic oscillation (20). These climate systems
may, for example, result in prolonged severe snow and ice conditions over several consecutive years, causing catastrophic mortality.
According to Fig. 2, the 1960s and 1970s corresponded to low
numbers in several Rangifer populations of Alaska and QuébecLabrador, whereas the 1860–1950 period points to generally low
caribou abundance in western Greenland, although the fit between
regional populations is not always perfect. Little comparable data
exist for Eurasia. Trends suggest that reindeer numbers might have
been low during the 1950s in northern Russia, although the time
series are often short and confounded by human intervention on
wild populations (via reindeer breeding and extensive hunting) and
conflicts in population size estimates (21). Regional synchrony in
population lows is likely to have a negative impact on human
50 兩 www.pnas.org兾cgi兾doi兾10.1073兾pnas.0709372104
densities by decreasing opportunities to secure food in times of crisis
from relatives and friends established in other communities (the
‘‘safety net’’) and by reducing the probability of finding higher
Rangifer density in adjacent areas.
Recent studies also suggest that fluctuations in Rangifer abundance increase with latitude, a pattern attributed to a south-tonorth weakening of density dependence and to the increasing effect
of stochastic abiotic factors along the same gradient (18, 20).
Therefore, under severe climatic conditions, Rangifer-dependent
foragers would have been more susceptible to demographic fluctuations compared with Rangifer-dependent foragers living in more
permissive environments.
In summary, three aspects of Rangifer population dynamics may
influence human population densities: (i) the high amplitude of the
Rangifer fluctuations in abundance, (ii) the tendency for some
Rangifer populations to decline synchronously at a regional scale,
and (iii) the trend toward more frequent fluctuations of greater
magnitude in Rangifer abundance with deteriorating climatic conditions and/or increasing latitude. How do these findings fit into our
understanding of human demography during the late Pleistocene?
Morin
D
E
F
EJJ
EJM
EJF
EJO sup
EJO inf
p
EJOP su
EJOP inf
EGPF
Fig. 3. The Saint-Césaire stratigraphy (modified from ref. 24, pp. 10 and 11).
From bottom to top: EGPF corresponds to a Denticulate Mousterian occupation, EJOP sup to a Châtelperronian occupation, EJO sup to a ProtoAurignacian occupation, EJF to an Early Aurignacian occupation, and EJM and
EJJ to two Evolved Aurignacian occupations. EJOP inf and EJO inf are small
occupations with unclear cultural attribution.
The Saint-Césaire Faunal Record
In 1979, a Neanderthal skeleton was found at the base of a
limestone cliff at Saint-Césaire in Charente-Maritime, France,
associated with Châtelperronian artifacts, an EUP industry then
attributed to modern humans (22). This finding had important
repercussions because it indicated that Neanderthals were involved
in the emergence of the Upper Paleolithic.
Further work at Saint-Césaire revealed a high-resolution stratigraphy covering the full span of the M/UP transition. Fifteen
occupations, thermoluminescence-dated between 30 and 43 kyBP
(23), along with several thousand artifacts and animal remains were
uncovered during the excavations (24). In this sequence (Fig. 3),
levels EGPF through EJJ are particularly important because they
document the M/UP boundary. Level EGPF corresponds to a
Denticulate Mousterian occupation, EJOP sup to a Châtelperronian occupation, EJO sup to a Proto-Aurignacian occupation, EJF
to an Early Aurignacian occupation, and EJM and EJJ to two
distinct Evolved Aurignacian occupations. EJOP inf and EJO inf
are small occupations for which the cultural attribution is less
secure.
The abundance of burned and cut-marked specimens and the low
incidence of carnivore remains and carnivore-modified bones in the
faunal samples indicate that humans were the main accumulators
of the faunal remains at Saint-Césaire (25). Furthermore, the high
␦15N value found in western European Neanderthals, including the
St Césaire 1 specimen (11), indicate that most of their dietary
proteins came from large herbivores. This finding strengthens the
use of the Saint-Césaire fauna for examining changes in human
population densities in Late Pleistocene Europe. Lastly, a study of
bone refits has shown that occupation mixing has been limited at
Saint-Césaire (26). These results support the potential of the
stratigraphy of this site for addressing fine-grain research questions.
Reindeer, steppe bison, and horse represent 96% of total species
composition for the Saint-Césaire occupations (Table 2). These
Large species
Reindeer
Steppe bison
Red deer
Megaceros
Roe deer
Wild boar
Horse
Wooly rhino
Wild ass
Mammoth
Spotted hyena
Wolf
Arctic fox
Polecat
Pine marten
Lynx
Badger
Cave lion
Hare
Total
Micromammals
Narrow-skulled vole
Common vole
Ground squirrel
Snow vole
Water vole
Pine vole
Garden dormouse
Root/Male vole
Collared lemming
Total
Mousterian
EGPF
Châtelperronian?
EJOP inf
Châtelperronian
EJOP sup
Proto-Aurignacian
EJO sup
Aurignacian I
EJF
Evolved
Aurignacian
EJM
Evolved
Aurignacian
EJJ
(n ⫽ 866)
24.7
38.0
1.0
0.8
—
—
34.1
0.2
—
0.8
0.2
0.1
—
—
—
—
—
—
—
99.9
(n ⫽ 9)
55.6
22.2
—
11.1
11.1
—
—
—
—
100.0
(n ⫽ 285)
33.0
35.8
2.5
0.4
—
0.4
26.3
0.4
—
0.7
—
0.7
—
—
—
—
—
—
—
100.2
(n ⫽ 2)
50.0
—
—
—
50.0
—
—
—
—
100.0
(n ⫽ 803)
20.2
48.7
5.1
—
0.5
0.5
17.4
3.5
0.2
2.6
0.4
0.2
0.2
0.1
—
—
—
0.2
—
99.8
(n ⫽ 38)
76.3
10.5
—
—
13.2
—
—
—
—
100.0
(n ⫽ 411)
84.9
4.6
0.5
—
—
—
5.4
0.7
—
1.9
—
0.7
0.2
0.2
0.5
—
—
—
0.2
99.8
(n ⫽ 84)
95.2
1.2
—
—
3.6
—
—
—
—
100.0
(n ⫽ 3,432)
82.3
4.8
0.3
0.2
—
0.0
11.2
0.2
—
0.5
0.0
0.3
0.1
0.0
—
0.0
0.0
0.1
—
100.0
(n ⫽ 69)
85.5
1.4
1.4
—
11.6
—
—
—
—
99.9
(n ⫽ 829)
72.4
9.4
0.2
—
—
—
13.6
0.1
—
4.0
—
0.1
—
—
—
—
0.1
—
—
99.9
(n ⫽ 100)
93.0
—
1.0
—
4.0
.
1.0
1.0
—
100.0
(n ⫽ 327)
69.1
11.9
0.6
—
—
—
17.4
—
—
0.3
0.3
0.3
—
—
—
—
—
—
—
99.9
(n ⫽ 109)
89.0
6.4
0.9
—
0.9
0.9
.
0.9
0.9
99.9
Antlers excluded. Micromammal data are from Morin (25) and Marquet (28).
Morin
PNAS 兩 January 8, 2008 兩 vol. 105 兩 no. 1 兩 51
ANTHROPOLOGY
Table 2. Large species and micromammal species composition in the Saint-Césaire levels
EUP, the same factor is expected to have reduced micromammal
species diversity as well, based on latitudinal trends in modern
analogues (8). Furthermore, if the climatic hypothesis is correct, the
trend toward increasing reindeer abundance at Saint-Césaire
should be associated with a significant increase in the abundance of
cold-adapted micromammals.
Both predictions are met by the data. The increasing abundance
of reindeer in the Saint-Césaire sequence is matched by a concomitant increase in the abundance of the narrow-skulled vole, a
cold-adapted species. Importantly, the decline in the diversity of
large species in the EUP of Saint-Césaire is accompanied by a
marked decline in micromammal species diversity (Fig. 4a). The
correlation between micromammal species diversity and sample
size is not statistically significant (rs ⫽ ⫺0.77, P ⬎ 0.05). These data
indicate that changes in faunal composition at Saint-Césaire were
induced by increasingly cool climatic conditions. These faunal
changes are in agreement with those observed at Roc de Combe
and Grotte XVI (10, 12) in France, and they suggest that this
climatic deterioration occurred on a regional scale. Additionally,
the high number of reindeer-dominated Aurignacian assemblages
in the same region (27) lends support to the climatic deterioration
inference.
Fig. 4. Faunal diversity at Saint-Césaire and its presumed impact on human
densities. (A) Large mammal versus micromammal species diversity, as measured by the reciprocal of Simpson’s index, in the Saint-Césaire levels. Data are
from Table 2 (EJOP inf and EJO inf assemblages excluded because of small
sample size). (B) Hypothetical reconstruction of fluctuations of hunter–
gatherer densities in western Europe during the Late Pleistocene. The reconstruction is based on an extrapolation of the presumed effects of mammal
diversity on human population densities. The shaded area shows the transition between the Châtelperronian and the Early Aurignacian.
three species are well represented in the Denticulate Mousterian
(EGPF), Châtelperronian? (EJOP inf), and Châtelperronian
(EJOP sup) occupations. In contrast, reindeer increased dramatically in abundance in the overlying Aurignacian occupations, reaching percentages from 69% to 85%. This increase is highly significant
(Châtelperronian versus Proto-Aurignacian; ts ⫽ 23.27, P ⬍
0.0001).
The temporal increase in reindeer abundance at Saint-Césaire is
associated with a sharp decline in species diversity (Fig. 4a). This
contraction of the species spectrum is consistent with the hypothesis
of a climatic deterioration during the M/UP transition (10) because
it is not correlated with sample size (rs ⫽ ⫺0.03, P ⬎ 0.05).
However, cultural factors—for instance, specialization on reindeer
(27)—also may explain these temporal patterns. To examine this
possibility, micromammal species (⬍500 g) recovered from the
Saint-Césaire occupations were used as control data and compared
with the other larger species at the site. Micromammals are helpful
because they typically represent background deposition in Pleistocene assemblages and are sensitive to subtle climatic changes (28).
The narrow-skulled vole (Microtus gregalis), common vole (Microtus arvalis), and water vole (Arvicola terrestris) comprise 98% of
the micromammal species identified at Saint-Césaire (Table 2).
Other micromammal taxa (n ⫽ 6) are poorly represented. Today,
the narrow-skulled vole is restricted to Palearctic tundra and
wooded steppe habitats, whereas the common vole and water vole
are typical of more temperate environments (29). If a climatic
deterioration induced a decline in large species diversity during the
52 兩 www.pnas.org兾cgi兾doi兾10.1073兾pnas.0709372104
Discussion
Assuming that the ecological relationship found between hunter–
gatherer density and mammalian species diversity extends to the
past, the reduction of species diversity in the EUP of Saint-Césaire
is likely to have resulted in significant demographic changes in
human populations. Human population densities not only likely
declined during this period, but they also were subject to more
extreme fluctuations relative to the final Mousterian (Fig. 4b).
These high-amplitude fluctuations would have been induced by a
growing reliance on Rangifer, a highly fluctuating resource. This
evidence suggests that the EUP in the region north of the Pyrenees
and the Alps corresponded to a period of niche contraction for
human populations. On a broader temporal scale, faunal (10, 30)
and climatic (31, 32) data indicate that this EUP pattern continued
through much of the western European Upper Paleolithic, because
little evidence for an expansion of the diet breadth exists for this
region before ⬇16,000 BP (33, 34). Specifically, fluctuations in the
number of humans are expected to have been most extreme, and
densities lowest, during the last Glacial Maximum (27,000–16,000
BP), when northern Europe became depopulated (35, 36).
These data also have implications for the human biological
transition at the time of the M/UP archeological transition. The
contribution of archaic sapiens, especially the Neanderthals, to the
modern human phylogeny is the subject of considerable debate.
The ‘‘replacement hypothesis’’ has stipulated that archaic sapiens
were replaced 40,000 to 35,000 years ago by modern humans
expanding out of Africa (see references in ref. 37). However, recent
studies suggest that the level of gene flow between these populations might have been underestimated (38–41). The results presented here are difficult to reconcile with the ‘‘replacement’’ (demic
expansion) hypothesis.
In France, the purported modern human expansion is said to
have occurred during the Châtelperronian and Early Aurignacian
(27). However, the Saint-Césaire data suggest that a climatic
deterioration during this period fueled a contraction of the human
niche. In this context, the probability that a large-scale expansion
into an occupied territory occurred and met with success appears
to be low. Futhermore, given that the M/UP transition is marked by
great stability in subsistence strategies (25, 30). Therefore, although
replacement of local populations by out-of-Africa migrants might
have contributed in shaping human biological evolution in western
Europe during the EUP, this factor was probably of secondary
importance.
A scenario emphasizing bottlenecks, genetic drift, and gene flow
therefore is favored over population replacement hypotheses for
Morin
Conclusion
Terrestrial ecosystems changed greatly during the EUP in western
Europe. The Saint-Césaire data suggest that a climatically induced
reduction of species diversity in the EUP caused declines in human
population densities. Furthermore, a reliance on reindeer, a highly
fluctuating resource, would have promoted recurrent bottlenecks in
the thinly scattered populations spread north of the Pyrenees and
the Alps. These data also suggest that models building on in situ
mechanisms, particularly population bottlenecks and genetic drift,
may provide more satisfactory explanations of the evolutionary
pathways taken by western European human populations during
the M/UP transition than those relying mostly on demic expansion
or replacement scenarios.
evaluated based on the reciprocal of Simpson’s index (1/D). D is calculated as
follows:
D⫽
冘
n共n ⫺ 1兲
,
N共N ⫺ 1兲
where n is the total number of identified remains for a particular species and N
the total number of identified remains for all species. Unspecified taxa and fish
species were excluded.
Because Middle Paleolithic and EUP foragers rarely included animal resources
other than mammals in their diet, nonmammalian species were excluded from
the analysis of the ethnographic and wildlife data. In these comparisons, terrestrial mammalian species include all native species present today at the specified
coordinates, marine mammals excluded. Human groups for which hunting represented ⬍45% of their subsistence activities, following the classification of
Murdoch (45), also were excluded. A higher hunting threshold (e.g., 80%) was not
adopted here to preserve adequate sample size.
Some of the human density estimates used in the analysis here are very rough,
making these data less than optimal. For instance, many estimates are derived
from 18th and 19th century accounts made by travelers and missionaries. Moreover, some of these estimates were produced in the postcontact period, and
therefore are probably underestimations because of the negative effects of
diseases and the geographical expansion of Europeans on native populations [see
Keeley (4) for a fuller discussion of these and other limitations concerning these
estimates]. Also, historical shifts in wild mammal distribution induced by human
settlement and overhunting (e.g., the dramatic range reduction of bison in the
19th century) and other factors (e.g., the introduction of firearms and horses) also
affect the accuracy of the correlations. Despite these important limitations, it is
thought that they do not completely alter the overall structure of the data.
Ungulate abundance is estimated based on the number of identified specimens,
whereas the minimum number of individuals is used to measure rodent abundance. Percentage comparisons of ungulate abundance are made by using the
arcsine transformation [denoted Ts (ref. 44, pp. 419 – 422)]. Species diversity is
ACKNOWLEDGMENTS. I thank Serge Couturier, Cédric Beauval, Frank Miller,
John Speth, and Robert Whallon for comments on earlier versions of this
manuscript and François Lévêque and Jean-Claude Marquet for discussions on
Saint-Césaire. Funding for the analysis of the Saint-Césaire material was
provided by the Fonds Québécois de la Recherche sur la Société et la Culture,
the Social Science and Humanities Research Council of Canada, the National
Science Foundation, the Service Régional d’Archéologie, Poitou-Charentes
region, and the CELAT Research Center, Université Laval.
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Materials and Methods
Morin
PNAS 兩 January 8, 2008 兩 vol. 105 兩 no. 1 兩 53
ANTHROPOLOGY
explaining the M/UP transition. It is hypothesized that the contraction of the human niche during the EUP promoted recurrent
bottlenecks in western Europe. Combined with genetic drift, pervasive in small populations (1), these recurrent bottlenecks could
account for the progressive loss of archaic traits in the local
populations. The small and decreasing effective size of western
European human populations versus the much larger, and possibly
expanding, effective size of the human populations from Africa may
have contributed to the process (42). Furthermore, the inferred
spatial extension of social relations in the Aurignacian (27), a
strategy that helps to buffer resource stress (43), might have
contributed to the rise in frequency of modern human traits in the
declining populations.