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Evolutionary changes in the masticatory complex following the transition to farming in the southern Levant.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 135:136–148 (2008)
Evolutionary Changes in the Masticatory Complex
Following the Transition to Farming in the
Southern Levant
R. Pinhasi,1* V. Eshed,2 and P. Shaw3
1
Department of Archaeology, University College Cork, Cork, Ireland
Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
3
School of Human and Life Sciences, Roehampton University, Holybourne Avenue, London,
SW15 4JD, United Kingdom
2
KEY WORDS
dental crown reduction; selective pressures; transition to agriculture; Levant
ABSTRACT
A post-Pleistocene reduction trend in the
dimensions of the masticatory complex followed the transition to agricultural lifestyle in several world regions. A
major limitation of previous studies is large temporal gaps
between the analyzed skeletal populations, which do not
allow the detection and analysis of a diachronic morphological transition. In this work, we analyze a large number
of specimens from the southern Levant, where agriculture
first emerged in situ and for which there is a good diachronic sequence of the shift from a hunting-gathering
way of life to a food producing, farming economy (12,000–
7,000 uncalibrated bp). Changes in the masticatory complex are examined in the context of three prevailing dental
reduction models: the Probable Mutation Effect (Brace,
1963; Brace and Mahler, 1971), Increasing Population
Density Effect (Macchiarelli and Bondioli, 1986) and Selective Compromise Effect (SCE) (Calcagno, 1989). A series of
linear regressions of dimension vs. time and coefficients of
variation for each dimension are analyzed. Our results
indicate significant reduction in the buccolingual but not
mesiodistal dental dimensions and in the ramus breadth
and anterior height dimensions of the mandible but not in
its overall size. These findings, taken together with low
coefficients of variation for the buccolingual dimensions,
suggest selective pressure resulting in reduction of specific
dimensions. The observed trend is in partial accordance
with the SCE but differs from the trends observed in other
regions, and is therefore best explained as a region-specific
variant of the SCE. Am J Phys Anthropol 135:136–148,
2008. V 2007 Wiley-Liss, Inc.
The Levant is the region in which some of the world’s
earliest farming communities first emerged. The transition between foraging and food production economies in
the Levant was a major threshold in human prehistory
and involved profound changes in mobility, social organization, subsistence, and technology (Henry, 1989; Kuijt,
1994; Eshed et al., 2004a,b, 2006). In the southern Levant, the early Holocene Natufian culture (12,500–
10,200, uncalibrated radiocarbon years before present;
henceforth: ‘‘uncal bp’’) marks the onset of the transition
to a fully sedentary lifestyle with a subsistence base that
continues to rely on hunting, gathering, and foraging
(Belfer-Cohen, 1991). It is generally divided into three
major chronological phases: Early (11,700–11,300 uncal
bp), Middle (recent) (11,300–10,500 uncal bp), and Final
(late) (10,500–10,300 uncal bp) (Bocquentin et al., 2001;
Valla et al., 2004; Fig. 1).
The first agricultural communities in the Levant
emerged during the succeeding Pre-Pottery Neolithic A
period (PPNA, 10,000–9,200 uncal bp), with a subsistence base that combines reliance on cultivation of
domestic cereals and legumes, the collection of wild
seeds and fruits, and hunting (Bar-Yosef, 1989; Kuijt,
1994). The PPNA displays architectural, technological,
and artistic attributes that indicate cultural continuity
with their Natufian predecessors (Banning, 1998). By
the middle of the following Pre-Pottery Neolithic B period (PPNB, 9,200–8,100 uncal bp) the subsistence base
shifted to include domestic cereals and a growing reliance on domesticated livestock (cattle, pigs, goats, and
sheep). It marks the peak of the Pre-Pottery Neolithic
period in terms of cultural uniformity across a wide geographic sphere of interaction, complex architecture, technology, and art (Aurenche and Kozlowski, 1999). The
Pre-Pottery Neolithic C (PPNC, 8,100–7,600 uncal bp)
was a short transitional period, which is associated with
the gradual decline of the PPNB, possibly due to overexploitation of resources (Galili et al., 2005). The Pottery
Neolithic period (PN, 7,600–7,000 uncal bp) marks the
end of a transformation from a hunter-gatherer socioeconomic system to a fully agricultural economy, the introduction of pottery, and the end of hunting (Orrelle and
Gopher, 2000).
Pronounced reduction in jaw and tooth dimensions
was reported among Early Holocene populations from
Europe (Brace et al., 1987; y’Edynak, 1989; y’Edynak
and Fleisch, 1983), North Africa (Chamla, 1980); Nubia
(Greene, 1972; Carlson and van Gerven, 1977; van
Gerven et al., 1977; Calcagno, 1986, 1989); and the Near
East (Dahlberg, 1960; Smith et al., 1984, 1986). Some of
C 2007
V
WILEY-LISS, INC.
C
Grant sponsors: Irene Levi-Sala CARE Foundation, National Geographic Society, Israel Science Foundation.
*Correspondence to: Ron Pinhasi, Department of Archaeology,
University College Cork, Cork, Ireland. E-mail: r.pinhasi@ucc.ie
Received 7 February 2007; accepted 8 August 2007
DOI 10.1002/ajpa.20715
Published online 28 November 2007 in Wiley InterScience
(www.interscience.wiley.com).
EVOLUTIONARY CHANGES IN THE MASTICATOR COMPLEX
137
Fig. 1. Map of the Natufian and Neolithic sites, by period.
the observed reduction trends were addressed in the context of the transition from hunter-gatherer to a fully
Neolithic lifestyle (cf. Greene, 1972; Carlson and Van
Gerven, 1977; Armelagos et al., 1989; Calcagno, 1989;
Larsen, 1995, 1997). These post-Pleistocene cranio- dental
changes took place in a relatively short period in evolutionary terms (Hillson, 2005). The following models have
been proposed to explain reduction trends in one or more
of the above mentioned regions:
a. The Probable Mutation Effect (PME) suggests that in
the absence of natural selection, mutations will be the
main force acting towards a reduction of structural
size and complexity of teeth and other organs. Thus,
developmental processes, controlled by complex
genetic mechanisms, will be disrupted resulting in an
incomplete or a simplified dental structure (Brace,
1963; Brace and Mahler, 1971). Brace and Mahler
(1971) hypothesized that the invention and use of pottery during the early Holocene and the subsequent
changes in food preparation techniques led to a relaxation of selective forces on the masticatory apparatus
and the onset of PME, which resulted in a consequent
decrease in tooth size.
b. Increasing Population Density Effect (IPDE) suggests
that reduction in dental crown size was mainly
derived from changes in population densities associated with the transition to a sedentary lifestyle. Thus,
the new post-Pleistocene environmental conditions
were associated with a new set of adaptive pressures.
These triggered a selection for reduction in nutritional and metabolic requirements, which led to a corresponding reduction in body size. Reduction in tooth
size was therefore a byproduct of selection for smaller
body size (Macchiarelli and Bondioli, 1986).
c. Selective Compromise Effect (SCE) is a model that
was introduced by Calcagno, based on his study of
reduction trends in post-Pleistocene Nubian populations (1986, 1989). It proposes that larger morphologically-complex crowns provide more surface area for
caries, which in turn can significantly affect the individual’s fitness. However, large crown area is essential
for the mastication of abrasive foodstuff. In the case
of populations who undergo a subsistence shift following the transition to agricultural economy, a selective compromise must occur between a selection for
smaller teeth with less complex cusp pattern and thin
enamel and a selection for bigger teeth with thicker
enamel to counter occlusal wear. A central aspect of
this model is the assumption that selection for smaller
dentition is triggered by dental crowding and high prevalence of cariogenic disease (cf. y’Edynak and Fleisch,
1983; Calcagno and Gibson, 1988; y’Edynak, 1989),
which is evident in Near Eastern and Nubian early
Holocene archaeological populations (Dahlberg, 1960;
Smith et al., 1984; Calcagno, 1986; Eshed et al., 2006).
American Journal of Physical Anthropology—DOI 10.1002/ajpa
138
R. PINHASI ET AL.
The above models provide three different approaches to
the observed mandibular and dental reduction among
agricultural populations. The PME essentially suggests
mutation as the predominant mechanism that induces
morphometric change and is hence a stochastic microevolutionary model. Both the IPDE and SCE models
emphasize the role of selective pressures in the dental
reduction process. However, the IPDE model views dental reduction as a byproduct of selection for smaller body
size following the decrease in nutrition and an increase
in population densities during the Neolithic period
(Machiarelli and Bondioli, 1986) while the SCE emphasizes functional-based reduction in teeth dimensions as
the direct outcome of balancing selective pressures (Calcagno, 1989).
Each of the above models for post-Pleistocene dental
reduction is associated with a set of specific assumptions
and predictions (see also Christensen, 1998):
Model 1 (PME): All dental dimensions are reduced
indicating a general decrease in size over time, variation in all dimensions either increases or remains
constant over time.
Model 2 (IPDE): Overall reduction in the main mandibular and dental dimensions and a corresponding
reduction in their metric variation. This condition
must be associated with evidence of decrease in
overall health and a decrease in stature that began
following a transition to sedentary lifestyle (cf. Macchiarelli and Bondioli, 1986).
Model 3 (SCE): Overall reduction in the main mandibular dimensions and a corresponding reduction in all
or a specific set of dental dimensions [i.e. total change
in overall crown area, or a uniform trend of change
in length or breadth dimensions that may potentially
and differentially affect certain tooth groups (e.g. posterior dentition to reduce prevalence of caries)], and
in their corresponding metric variation.
A major limitation of previous studies on post-Pleistocene dental and mandibular reduction trends was that
their skeletal samples did not include representative
specimens from the period of transition. While Levantine
jaw and dental reduction trends were previously studied
by Smith et al. (1984, 1986), their results were compromised by the limited sample size and combining specimens to groups that do not correspond to specific
archaeological phases and hence do not provide the sufficient resolution to address changes in the masticatory
complex in relation to specific cultural changes. It therefore remained unclear what sort of changes in the masticatory complex occurred in this region. The availability
of Natufian and Neolithic specimens that were recovered
during the last 2 decades from excavations in Israel
offers a unique window into the study of morphological
change in human populations (Fig. 2). In this region,
this process began with the transition to a fully sedentary lifestyle (Natufian Period), followed by an increase
in the reliance on cereals during the PPNA, the introduction of domestic livestock (Mid-PPNB) and eventually
the introduction of pottery (PN). Hence, a major issue in
the Levantine diachronic sequence is whether the intensity and particular pattern of a process of dental and jaw
reduction occurred in a uniform manner across the total
time span, or rather drastically changed in intensity and
pattern following the transition between the Natufian
and PPNA periods (hence representing a ‘‘punctual’’
Fig. 2. A schematized chronology of the Natufian and Neolithic cultures of the Levant based on uncalibrated 14C dates,
and associated skeletal samples utilized in this study.
rather than a continuous trend). Moreover it is of interest to examine whether the invention of pottery resulted
in the intensification of existing reduction trends as suggested by the PME model.
In this study we investigate the following:
1. The nature of the reduction trend: (a) which crown
dimensions and mandibular dimensions are significantly reduced over time; and (b) is there any evidence to suggest that the trend intensified or reduced
in magnitude during (i) the early Neolithic period
(PPNA onwards) and/or (ii) the PN period.
2. Assuming that a significant reduction trend is observed, we investigate which of the above models best
fit our data by assessing the obtained results in conjunction with published reports on diachronic changes
in the prevalence of dental pathologies (Eshed et al.,
2006), stature (Smith et al., 1984), cranial dimensions
(Pinhasi, 2004); and overall health (Smith et al., 1984).
Subsequently, we address the relationship between the
observed trend and those reported for other populations
that underwent a similar cultural/economic transition to
inspect whether some of its aspects are universal among
post-Pleistocene populations that underwent a transition
to agricultural economy.
MATERIAL AND METHODS
We analyzed a total sample of 242 individuals (some of
which are represented by only few isolated teeth) from
five archaeological periods (Table 1, Fig. 1). Only some of
the archaeological phases from which the skeletons were
recovered are associated with radiocarbon dates for their
specific layer/context. The rest were given an average
uncalibrated date in years before present (uncal bp) for
American Journal of Physical Anthropology—DOI 10.1002/ajpa
139
EVOLUTIONARY CHANGES IN THE MASTICATOR COMPLEX
TABLE 1. Summary table of chronology, sites, and number of specimens
a
Date
Lab no.
References
2
13
Natufian (ancient)
Natufian (ancient)
11700 2 11300 BP
11700 2 11300 BP
11590 6 540
RANGE
RANGE
Ly-1660
Ein Mallahab
9
Natufian (recent)
11300 2 10500 BP
RANGE
Ein Mallahab
15
Natufian (final)
10500 2 10300 BP
RANGE
Hayonim Cave
Hayonim Cave
12
7
Natufian (ancient)
Natufian
(recent 5 middle)
12010 6 180
11300 2 10500 BP
OXA-743
RANGE
Garfinkel, 1999
Belfer-Cohen, 1988;
Bocquentin et al.,
2001; Valla et al., 2004
Belfer-Cohen, 1988;
Bocquentin et al.,
2001; Valla et al., 2004
Bocquentin et al., 2001;
Valla et al., 2004
Belfer-Cohen, 1988
Belfer-Cohen, 1988;
Bocquentin et al.,
2001; Valla, 2004
Belfer-Cohen, 1988
Site
Period
N
Areq el Ahmar
Ein Mallahab
Rakefetb
4
Nahal Oren
Nahal Orenb
Hatoulab
10
6
7
Natufian recent
and final
Natufian (middle)
Natufian (Late)
PPNA
Jericho
Abu Hureyrac,d
Abu Hureyrad,e
Abu Hureyraf
Abu Hureyrad,g
Abu Ghosh
Yiftahelb
Bananab
Abu Madib
Nahal Betzetb
Nahal Oren
Neolithicb
Kefar Hahoreshb,h
11
4
6
5
3
22
6
7
4
1
6
PPNA
PPNB
PPNB
PPNB
PPNB
PPNB
PPNB
PPNB
PPNB
PPNB
PPNB
9551 6 63
8676 6 72
8330 6 100
8190 6 77
8490 6 100
60 6 8895
8870 6 90
9200 2 8100
9200 2 8100
8330 6 100
9200 2 8100
28
PPNB
8650 6 50
RTT-3733.1
9
3
PPNB
PPNB
8710 6 150
8155 6 50
BM-253
GrN-14538
31
3
PPNC
PN
7755BP 6 55
7050 6 100
RT2495,93
RT-1642
PN
PN
7600 2 7000
6565 6 70
RANGE
RT724
b
d
Jericho
Bastai
Atlit Yamb
Lod (Neve Yaraq)b
Tell Roim Westb
Neve Yama
4
4
10980 6 260
11300 2 10500 BP
10490 6 430
10030 6 140
I-7032
RANGE
SMU-9
GifA 91360
BM-1327
BM-1423
Oxa-2168
BM-1424
OxA-878
RT-2453
Pta-4242
RANGE
RANGE
RT-1394
RANGE
Noy, 1989
Belfer-Cohen, 1988
Lechevallier and Ronen,
1994
Burleigh, 1983
Burleigh et al., 1982
Housley, 1994
Burleigh et al., 1982
Housley, 1994
Segal and Carmi, 2003
Garfinkel et al., 1987
Hershkovits pers. com.
Hershkovits pers. com.
Carmi and Segal, 1992
Noy et al., 1973
Goring-Morris et al.,
2001
Burleigh, 1983
Muheisen. and Gebel,
1987
Galili, 2004
Gopher and Blockman,
2004
Dani Nadel pers. com.
Wreschner, 1977
PA is the Period’s average date in uncalibrated years BP, entries for Neolithic specimens are from the chornological table published
by Garfinkel (1999). Natfufian chronology is based on Valla et al., 2004; Bocquentin et al., 2001; Belfer-Cohen, 1988.
a
Based on number of specimens.
b
Department of anatomy and anthropology, Tel Aviv University, Israel.
c
Phase 6, Trench C.
d
Natural History Museum, London.
e
Phase 5, Trench E.
f
Trench B.
g
Trench D, Levels 68, Phase 4, Trench D.
h
Based on Minimum Number of Individuals-MNI.
i
Anatomy Centre University of Göttingen, Germany.
the period with which they are associated, based on the
Levant Neolithic chronology published in Garfinkel (1999).
The most commonly applied dental measurements are
the maximum length and breadth dimensions of the
tooth crown, also known as the mesiodistal and buccolingual diameters, respectively. Buccolingual and mesiodistal
dimensions were measured using the method of Moorrees
(1957). All left-sided teeth were measured except when
missing, worn, or poorly preserved. In such cases, the
right side antimeres were used instead. Loose dentition
that could be assigned to the correct anatomical position
was also measured when associated archaeological documentation indicated that it belongs to a single specimen.
We excluded all mesiodistal dimensions when inter-proximal wear or pathology resulted in reduction of the over-
all crown length and buccolingual dimensions when occlusal wear or pathology reduced the overall crown
height below the point at which maximum breadth
dimension appear to have been located (cf. Christenen,
1998). Jaw dimensions were measured based on the
standard methodology specified in Bräuer (1988).
Specimens from the Department of Anatomy and Anthropology, Tel-Aviv University, were measured by RP
and VE. All other specimens were measured by RP. Data
consistency was assessed by examining inter-observer
error on a randomly selected subset of 22 Natufian specimens that was independently measured by RP and VE.
A t-test for two independent samples on the two data
sets showed that none of the means or standard deviations was significantly different at 99% confidence inter-
American Journal of Physical Anthropology—DOI 10.1002/ajpa
140
R. PINHASI ET AL.
TABLE 2. Linear regressions of teeth dimensions over time for the total set of specimens
Upper
N
r2
Slope mm/
1000 years
Sig.
F
Lower
N
r2
Slope
(mm/1000 years)
Sig.
F
I1MD
I1BL
I2MD
I2BL
CMD
CBL
P3MD
P3BL
P4MD
P4BL
M1MD
M1BL
M2MD
M2BL
M3MD
M3BL
77
78
69
70
105
106
92
91
90
90
107
107
89
88
64
63
0.043
0.061
0.067
0.010
0.000
0.036
0.026
0.181
0.026
0.152
0.000
0.122
0.002
0.112
0.013
0.150
0.100
0.070
0.098
0.039
0.004
0.091
0.086
0.228
20.067
0.191
0.001
0.185
20.029
0.217
20.085
0.260
Ns
*
*
Ns
Ns
Ns
Ns
**
Ns
**
Ns
**
Ns
**
Ns
**
0.9
1.4
0.1
1.5
0.8
3.4
0.1
0.2
0.6
0.1
3.7
1.6
0.0
0.0
0.1
0.2
I1MD
I1BL
I2MD
I2BL
CMD
CBL
P3MD
P3BL
P4MD
P4BL
M1MD
M1BL
M2MD
M2BL
M3MD
M3BL
71
72
89
91
119
120
128
129
125
122
148
151
150
151
107
104
0.002
0.254
0.004
0.136
0.044
0.099
0.024
0.249
0.002
0.082
0.010
0.144
0.015
0.075
0.007
0.068
0.023
0.177
20.027
0.164
0.081
0.158
0.026
0.234
20.021
0.125
0.054
0.171
0.061
0.151
0.050
0.145
Ns
**
Ns
**
*
**
Ns
**
Ns
**
Ns
**
Ns
**
Ns
**
0.7
0.1
0.2
1.1
0.1
2.0
0.6
0.0
0.8
1.2
0.5
0.0
0.6
0.7
0.0
4.9*
Slope values are in mm per 1000 years, Sig. indicates significant slope values at * 5 P \ 0.05, and ** 5 P \ 0.01.
val. None of the specimens was sexed since a large part
of the sample contained mandibles and crania without
postcranial remains. However, a previous study on the
skeletal samples from the Natufian and Pre-Pottery periods indicate a similar degree of sexual dimorphism across
the studied time interval (around 10%, Smith et al., 1984).
Linear regressions of change in dimension over time
were calculated for (a) the total set; (b) the Natufian and
Pre-Pottery Neolithic specimens (excluding the PN set)
to test reduction trends in the jaw and dentition. We analyzed 32 regressions of mesiodistal and buccolingual
dimensions representing the complete adult dentition
and nine regressions of mandibular measurements representing the main dimension of the mandibular corpus
and ramus. For each dimension studied, only regressions
with a statistically significant value for the regression
slope’s coefficient indicate a significant diachronic trend.
These were then examined to assess the magnitude and
direction of the change over time. Additionally, scatter
plots for all significant dimensions were visually examined to support the linearity in the observed trends.
We then analyzed whether the reduction trend has
changed in intensity following the transition from the
Epipalaeolithic (Natufian) to the Neolithic (PPNA-PN)
period. Analyses of Covariance (Ancova) were performed
to detect any significant difference in the magnitude of
the reduction trend for each dimension. The null hypothesis was that there is no significance difference in the
magnitude of the slope for a given dimension. A significant P value (set at P \ 0.05) indicates that the regression slopes for each period are different and that the
null hypothesis should be rejected.
The Coefficient of Variation (CV) provide a standardized way to compare the magnitude of morphological
variation in the dentition and other morphological structures (Sokal and Braumann, 1980):
CV ¼ 100
S
X
S, standard deviation and X, arithmetic mean.
For small sample size, a correction factor should be
applied:
CVc ¼ CVð1 þ ð1=4nÞÞ;
n, sample size (Plavcan and Cope, 2001).
Low CV values suggest that a given dimension is subject to directional selection (Mayr, 1963; Leamy and
Bader, 1970). While there have been some cases where
the amount of variation in the phenotype has increased
with directional selection (Guthrie, 1963), the majority of
studies indicate that directional selection is responsible
for a reduction in phenotypic variability (Frayer, 1978).
CVs were calculated for the data set to detect diachronic changes in variability of mesiodistal vs. buccolingual dimensions for (1) the total dental set (2) upper and
lower dentition, and (3) on the total set of dental dimensions by period, including the tripartite division of the
Natufian (Fig. 2). The sum of the mesiodistal mandibular
dimensions provides an estimate of the total length of
the lower dental arch. We used multiple imputations
software Norm V2.02 (Schafer, 1999) to replace missing
values for up to four teeth (but not from the same tooth
group) and then calculated the sum of half of the lower
arcade, multiplied by two to obtain an estimate of its
overall length. The low number of specimens with nearly
complete upper dentition did not allow the estimation of
a similar sum for the upper arcade. According to Sokal
and Baunmann (1980), it is only possible to compare
between two coefficients of variation from independent
samples by a conventional t-test when the distribution of
the sample coefficients approaches normality. Since some
deviation from normality was noted in the case of both
parameters, we applied a robust nonparametric test
(Wilcoxon for two related samples) to assess difference
between the CVs of mesiodistal and buccolingual dimensions of the lower dental arcade.
RESULTS
Dental data
Table 2 provides results of the regression analyses of
changes over in upper and lower mesiodistal and buccolingual dimensions (sample size, slope value, r2 value,
and significance value). All the buccolingual dimensions
of both the upper and lower dentition, with the exception
of upper second incisor and upper canine, were significantly reduced. The only mesiodistal dimensions that
were significantly reduced are those of the second upper
incisor and the lower canine. In total, 16 of the regression slopes are significant at P \ 0.05; out of which
American Journal of Physical Anthropology—DOI 10.1002/ajpa
EVOLUTIONARY CHANGES IN THE MASTICATOR COMPLEX
seven are of the upper dentition and nine of the lower
dentition and only two are of mesiodistal dimensions.
Thirteen of the regression slopes show a reduction rate
greater than 0.1 mm/1000 years (Table 2, bold ink); none
of which are of mesiodistal dimensions. These include all
the buccolingual dimensions of the lower dentition, and
the buccolingual dimensions of the posterior upper dentition (premolars and molars). Figure 3 illustrates some of
the regression slopes for both significant (buccolingual)
and nonsignificant (mesiodistal) dental dimensions. The
average slope value for the significant maxillary buccolingual dimensions is 0.19 and 0.17 mm/1000 years for
the mandibular dentition. The average slope value for
the buccolingual dimensions of the posterior maxillary
dentition is 0.22 mm/1000 years and 0.16 for the posterior maxillary dentition. The average slope rate for the
anterior buccolingual dimensions of the lower dentition
is 0.17 mm/1000 years. The average slope rate for the
significant mesiodistal dimensions is 0.09 mm/1000 years
and is therefore approximately half the rate of the average reduction in buccolingual dimensions. Table 2 also
provides the results of the Ancova for each dimension.
The only difference in slopes between the Natufian and
Neolithic sets was for in the case of the buccolingual
dimension of the lower third molar. Since P value was
set to (P \ 0.05) it was expected that at least one of the
32 slopes will flag significant by chance. Hence the null
hypothesis, that there is no significant difference in the
slope values of the Natufian vs. Neolithic sets, should
not be rejected.
Table 3 provides the results of the regressions on the
same data set excluding all PN specimens (11 in total).
The significance tests of the slopes yielded very similar
results. Three of the dimensions that were significantly
reduced in the previous analysis are nonsignificant in
the current test: the lower buccolingual dimension of the
third molar, the mesiodistal dimension of the upper second incisor, and the mesiodistal dimension of lower canine. The latter were only significant at P \ 0.05 in the
case of the analysis of the total set. In the current analysis, 13 of the regression slopes are significant at P \
0.05; out of which six are of the upper dentition and
seven of the lower dentition and all are of buccolingual
dimensions. Twelve of the regression slopes show a
reduction rate greater than 0.1 mm/1000 years (Table 3,
bold ink). These include all the buccolingual dimensions
of the lower dentition with the exception of the lower
third molar, and the buccolingual dimensions of the
posterior upper dentition (premolars and molars). It
therefore appears that the trend of significant reduction
in the buccolingual dimensions of all dentition and the
higher rate of reduction for the posterior upper dentition and all the buccolingual dimensions of the lower
arcade is not an artifact of the inclusion of the PN
group.
Results of the analysis of CV by period for the upper
and lower dentition are provided in Tables 4 and 5,
respectively. The nonparametric test on the total period
indicates a significant difference (P \ 0.01) between the
mesiodistal and buccolingual CVs. A significant difference (P \ 0.01) was also detected when analyzing each
jaw dimensions separately. Paired tests for each period
(except for PN due to small sample size) showed that differences are highly significant for the early/ancient
Natufian period, and the late/final Natufian period, but
nonsignificant for the middle/recent Natufian period and
for the PPNA, PPNB, and PPNC periods (Fig. 4).
141
The analysis of the sum of the mesiodistal mandibular
dimensions was used to estimate whether there were any
significant changes over time to the total length of the
lower dental arch. Regression of the sum of the lower
mesiodistal dimensions vs. time (in years bp) indicates no
significant trend while a regression of the average lower
buccolingual dimension per specimen over time shows a
statistically significant reduction trend (P \ 0.01).
Mandibular data
The regressions of change in each of nine mandibular
dimensions over time (in 1000 years) is provided in Table 6
(sample sizes, slope values, r2 values, and significance
values). It is evident that only the ramus breadth and
anterior symphyseal height dimensions were significantly reduced over the time period (Table 6). Since
ramus height and breadth dimensions are significantly
correlated (r 5 0.425, P \ 0.01, and n 5 72), the significant reduction in ramus breadth alone indicates a unidirectional change in the overall shape of the ramus as
it becomes narrower without a corresponding change in
height.
Figure 5 illustrates the regression slopes for the two
dimensions with a significant reduction trend (symphyseal height—A, and ramus breadth—C), which contrast
with the no significant change in the dimension of the
mandibular length (Fig. 5B).
The exclusion of the PN group (Table 7) did not
change the results but yielded a lower significance value
for the slope of the ramus breadth dimension (P \ 0.05).
The slope parameters indicate a slightly slower reduction rate in ramus breadth dimension (0.55 mm/1000
years) and for the symphyseal height dimension (0.795
mm/1000 years).
DISCUSSION
Our statistical analysis indicates reduction mainly in
the buccolingual dimensions of the posterior upper dentition and both the anterior and posterior lower dentition.
The reduction in dimension over time is significant for
14 out of the 16 buccolingual dimensions and in only 2 of
the 16 mesiodistal dimensions. The analysis of the mandibular dimensions shows that only two dimensions out
of the nine, the anterior symphyseal height and ramus
breadth, were significantly reduced. It therefore indicates a diachronic reduction trend that is nearly uniform
across the dentition and that is not associated with an
overall reduction of mandibular size, but rather with
particular changes in the corpus height at the mandibular symphysis and a reduction in ramus breadth.
The average slope value for the buccolingual dimensions is 0.17 mm/1000 years, which is a greater figure
than the one reported by Brace et al. (1987) for European Neolithic populations (0.049 mm/1000 years for the
average maxillary buccolingual dimension and 0.041
mm/1000 years for the average mandibular buccolingual
dimension). Brace et al. (1987) report that the rate of
reduction in buccolingual dimensions in general and in
maxillary dentition in particular is accelerated among
post-Pleistocene European populations when compared
with the rates among Late Pleistocene populations. Calcagno (1989) in his study of diachronic dental trends
among post-Pleistocene Nubian populations notes that
‘‘length dimensions do not reduce with nearly the consistency nor magnitude as the breadth, and some even dis-
American Journal of Physical Anthropology—DOI 10.1002/ajpa
142
R. PINHASI ET AL.
Fig. 3. Bivariate scatterplots of both significant (right column, A, C, E) and nonsignificant (left column, B, D,) regression slopes
of change in dental dimensions over time (in uncalibrated radiocarbon years). [Color figure can be viewed in the online issue, which
is available at www.interscience.wiley.com.]
American Journal of Physical Anthropology—DOI 10.1002/ajpa
143
EVOLUTIONARY CHANGES IN THE MASTICATOR COMPLEX
TABLE 3. Linear regressions of teeth dimensions over time for the total set excluding the Pottery Neolithic group
Upper
N
r2
Slope
(mm/1000 years)
Sig.
Lower
N
r2
Sig.
Slope
(mm/1000 years)
I1MD
I1BL
I2MD
I2BL
CMD
CBL
P3MD
P3BL
P4MD
P4BL
M1MD
M1BL
M2MD
M2BL
M3MD
M3BL
73
74
64
65
99
100
88
87
86
86
102
102
84
84
62
61
0.036
0.100
0.023
0.014
0.002
0.025
0.025
0.122
0.038
0.121
0.008
0.101
0.004
0.097
0.007
0.107
0.096
0.093
0.061
0.048
20.019
0.082
0.091
0.198
20.085
0.183
20.066
0.181
20.004
0.219
20.064
0.207
Ns
**
Ns
Ns
Ns
Ns
Ns
**
Ns
**
Ns
**
Ns
**
Ns
**
I1MD
I1BL
I2MD
I2BL
CMD
CBL
P3MD
P3BL
P4MD
P4BL
M1MD
M1BL
M2MD
M2BL
M3MD
M3BL
64
65
82
84
111
112
119
120
119
116
140
143
142
143
100
97
0.002
0.196
0.024
0.081
0.025
0.064
0.003
0.230
0.004
0.051
0.002
0.089
0.016
0.067
0.003
0.016
Ns
**
Ns
**
Ns
**
Ns
**
Ns
**
Ns
**
Ns
**
Ns
Ns
20.026
0.165
20.072
0.130
0.066
0.134
0.028
0.244
20.037
0.104
0.025
0.137
0.068
0.148
0.011
0.076
Slope values are in mm per 1000 years, Sig. indicates significant slope values at * 5 P \ 0.05, and ** 5 P \ 0.01.
play insignificant decreases.’’ Thus, our current results
do not stand in contrast to those reported by Brace et al.
(1987) and Calcagno (1989), but rather indicate a particularly pronounced reduction trend that mainly affects
the buccolingual dimensions of the Levantine populations.
Lack of significance in 14 out of the 16 mesiodistal
dimensions taken together with no significant reduction
in the mandibular size and estimated lower arch length
suggest that both the mandibular overall size dimensions and the overall dental arcade were not significantly reduced over time. The difference in the CVs for
mesiodistal vs. buccolingual dimensions suggest that
selective pressures acted on the buccolingual dimensions
and resulted in their overall reduction over time but
that these pressures did not act on the mesiodistal and
overall mandibular size dimensions. It therefore appears
that in the southern Levant, dental reduction was not
associated with a reduction in overall jaw dimensions as
was reported in the case of Nubia (Calcagno, 1989) and
Serbia (y’Edynak, 1989).
Which of the above models best explain this pattern of
mandibular and dental reduction? The PME model can
be rejected as a possible mechanism behind the observed
reduction trend since the data indicates a uniform
change in specific dimensions, which best fits a model of
directional selection rather than one that proposes the
accumulation of random mutations. Furthermore, the
exclusion of PN specimens from the analysis of dental
reduction did not significantly alter the overall dental or
mandibular reduction patterns. It therefore appears that
the observed trend continues during the PN period and
that more than likely, the development of pottery in the
Levant did not by itself mark a major shift in the dietary
habits of Levantine populations (also cf. Gopher, 1998).
Our results do not support the assumptions that
underlie the IPDE model. First, there is no reduction in
the overall size of the dentition but particularly in its
buccolingual dimensions. Secondly, there is no significant
reduction in overall mandibular size (no reduction in
mandibular corpus length and breadth dimensions). A
report on average stature of males and females during
the Natufian, PPNA, and PPNB periods in the southern
Levant region (Smith et al., 1984) shows no significant
decrease in stature following the transition to agriculture. Craniometric analyses on Natufian and PPNB popu-
lations show no evidence for overall gracilisation and
decrease in all cranial dimensions following the transition to agriculture (Pinhasi, 2004). Thirdly, the IPDE
assumes that selection for smaller body size would only
occur in response to overall deterioration in the health
status of the early agricultural populations. While deterioration in health was indeed reported in the case of
many world regions (cf. Larsen, 1995), it does not agree
with data for the southern Levant, which indicates no
evidence for the deterioration in overall health following
the transition (Smith et al., 1984). It therefore appears
that the IPDE does not provide a satisfactory explanation for the observed Levantine trend.
Our results are compatible with certain aspects of the
SCE model: evidence of selection for smaller buccolingual dimensions (low CV values) and a nearly uniform
reduction trend in this dimension. However, there is no
significant change over the span of this analysis in overall mandibular length (Fig. 4) or in lower dental arch
dimensions (as estimated from the sum of the mesiodistal dimensions of the lower dentition). This contrast with
significant reduction in ramus breadth and anterior
height dimensions.
The SCE model associates the reduction trends in dental dimensions following the transition to agriculture
with changes in the prevalence rates of two pathological
conditions: malocclusion and dental infections, which are
mainly the outcome of an increase in the prevalence
of caries (Calcagno, 1989; Larsen, 1997; Christensen,
1998). There is no published data on dental crowding
and malocclusion among the southern Levantine population. A recent study by Eshed et al. (2006) on the same
skeletal samples that were analyzed in this work reports
no significant differences in the prevalence of caries,
periapical lesions, and antemortem tooth loss between
the Natufian and Neolithic populations. However, the
study revealed a high prevalence of periodontal disease
(PD) among the Natufians, which is significantly reduced
during the PPN periods. According to Eshed et al.,
(2006) the differences in PD do not appear to be associated with changes in overall oral hygiene or in diet but
are most likely the outcome of physiological causes due
to the application of extensive occlusal forces in the mastication of abrasive food during the Natufian period.
This observation is further supported by evidence of differences in wear pattern among the two populations: the
American Journal of Physical Anthropology—DOI 10.1002/ajpa
American Journal of Physical Anthropology—DOI 10.1002/ajpa
LI1MD
LI1BL
LI2MD
LI2BL
LCMD
LCBL
LP3MD
LP3BL
LP4MD
LP4BL
LM1MD
LM1BL
LM2MD
LM2BL
LM3MD
LM3BL
UI1MD
UI1BL
UI2MD
UI2BL
UCMD
UCBL
UP3MD
UP3BL
UP4MD
UP4BL
UM1MD
UM1BL
UM2MD
UM2BL
UM3MD
UM3BL
3
4
7
7
9
9
9
9
8
8
8
8
9
9
8
8
N
6
6
8
8
10
10
10
10
10
10
11
11
12
12
7
7
N
1.51
0.49
0.76
0.48
0.34
0.62
0.50
0.97
0.83
0.74
0.68
0.74
1.11
1.52
1.02
1.45
5.30
6.77
6.05
6.95
7.10
8.61
7.17
8.63
7.13
8.88
10.99
11.35
10.79
11.16
10.60
11.11
Mean
1.01
0.37
0.57
0.42
0.40
0.50
0.64
0.51
0.71
0.41
1.24
0.53
1.00
0.55
0.77
1.04
SD
CV
7
8
6
7
10
10
10
10
11
11
13
12
12
12
9
9
N
9.02
7.61
7.05
6.66
7.14
8.43
6.91
9.66
6.60
9.84
9.87
11.95
9.83
11.92
9.43
11.26
Mean
0.42
0.21
0.32
0.91
0.78
0.91
0.92
0.90
0.27
0.63
1.73
0.80
0.78
0.64
0.70
0.80
SD
CV
4.68
2.74
4.48
13.70
10.92
10.77
13.29
9.34
4.13
6.38
17.48
6.70
7.89
5.35
7.44
7.08
Middle Natufian
9
9
8
8
15
15
18
18
17
17
15
15
11
11
7
7
N
8.97
7.22
6.84
6.56
7.25
8.63
6.75
9.43
6.32
9.42
10.16
11.69
9.05
11.87
8.71
11.35
0.53
0.40
0.63
0.38
0.65
0.54
0.74
0.56
0.48
0.67
1.19
0.81
0.91
1.09
1.11
0.61
SD
Final Natufian
Mean
5.87
5.49
9.21
5.72
8.91
6.26
11.03
5.98
7.61
7.11
11.69
6.92
10.03
9.22
12.70
5.41
CV
3
3
3
3
4
4
4
4
4
4
4
4
4
4
3
3
N
8.83
7.73
7.34
6.81
7.50
8.88
6.98
9.36
6.71
9.64
9.99
11.40
9.06
11.59
8.78
10.54
0.50
0.21
0.17
0.56
0.40
0.52
0.48
0.05
0.44
0.57
0.72
0.42
0.57
0.76
1.27
0.94
SD
PPNA
Mean
5.67
2.73
2.28
8.15
5.35
5.83
6.90
0.57
6.56
5.88
7.25
3.68
6.32
6.57
14.51
8.88
CV
29
29
24
24
39
39
24
24
23
23
35
36
30
30
21
21
N
8.87
7.32
6.81
6.74
7.73
8.55
7.04
9.24
6.95
9.04
10.70
11.60
9.98
11.66
9.22
10.87
0.66
0.39
0.65
0.62
0.49
0.68
0.54
0.53
0.57
0.78
0.74
0.73
0.97
1.00
1.08
0.75
SD
PPNB
Mean
11
11
11
11
13
13
13
13
12
12
15
15
13
13
10
10
N
5.65
6.44
5.78
6.48
6.96
7.93
6.66
8.42
6.62
8.48
11.10
11.29
10.62
10.89
10.52
10.20
Mean
1.50
0.52
1.05
0.78
0.71
0.88
0.59
0.65
0.37
0.77
0.71
0.51
0.43
0.70
0.42
0.36
SD
CV
26.57
8.04
18.19
12.06
10.15
11.05
8.89
7.70
5.62
9.07
6.39
4.56
4.10
6.39
3.96
3.54
Middle Natufian
8
8
7
7
10
10
13
13
13
12
15
15
16
16
16
16
N
5.18
6.31
5.96
6.82
6.86
7.71
6.74
8.27
6.68
8.49
10.84
11.02
10.62
10.75
10.55
10.46
Mean
0.49
0.47
0.77
0.81
0.44
0.69
0.38
0.41
0.67
0.46
0.89
0.64
0.73
0.67
0.75
0.74
SD
Final Natufian
9.40
7.49
12.91
11.94
6.39
8.95
5.65
4.99
9.97
5.41
8.19
5.77
6.91
6.25
7.13
7.12
CV
5
5
6
7
10
11
10
11
11
11
15
15
14
14
9
9
N
5.65
6.17
6.04
6.38
6.82
7.63
6.94
7.75
6.92
8.12
10.96
10.67
10.41
10.20
11.00
10.43
Mean
0.42
0.29
0.49
0.39
0.82
0.72
0.41
0.43
0.35
0.50
0.65
0.57
0.51
0.65
0.65
0.46
SD
PPNA
7.39
4.67
8.06
6.09
12.09
9.47
5.97
5.55
5.09
6.15
5.90
5.36
4.87
6.35
5.86
4.43
CV
23
23
30
30
44
44
43
43
44
42
51
52
58
58
42
39
N
5.53
6.11
6.18
6.50
6.84
7.80
6.95
7.89
7.05
8.34
10.99
10.80
10.61
10.53
10.43
10.27
Mean
0.27
0.43
0.41
0.45
0.45
0.55
0.50
0.53
0.46
0.54
0.63
0.63
0.63
0.81
0.95
0.66
SD
PPNB
TABLE 5. Tooth measurements and coefficient of variation of the lower dentition (all periods excluding PN)
16.39
6.63
10.89
6.93
4.26
7.06
6.98
9.99
12.45
7.56
6.29
6.02
11.29
12.59
11.14
12.78
CV
19.09
5.52
9.39
6.01
5.60
5.84
8.99
5.87
9.95
4.67
11.31
4.63
9.31
4.90
7.24
9.37
Early Natufian
9.25
7.46
6.96
6.86
7.87
8.86
7.10
9.75
6.70
9.76
10.74
12.34
9.84
12.10
9.20
11.35
SD
Early Natufian
Mean
TABLE 4. Tooth measurements and coefficient of variation of the upper dentition (all periods excluding PN)
4.85
7.07
6.66
6.93
6.55
7.11
7.21
6.67
6.55
6.44
5.78
5.81
5.90
7.67
9.12
6.43
CV
7.40
5.38
9.58
9.27
6.30
7.99
7.69
5.79
8.21
8.66
6.89
6.31
9.76
8.54
11.72
6.88
CV
6
6
10
11
13
13
17
17
16
16
20
22
17
18
7
7
N
11
11
9
9
10
10
8
8
11
11
14
14
8
8
8
7
N
0.46
0.32
0.22
0.40
0.51
0.50
0.56
0.47
0.50
0.31
0.93
0.54
0.99
0.97
1.46
0.92
5.34
5.92
5.99
6.39
6.65
7.65
6.76
7.63
6.99
8.24
10.78
10.70
10.37
10.25
10.26
10.53
Mean
0.59
0.39
0.38
0.35
0.38
0.51
0.42
0.61
0.45
0.54
0.80
0.45
0.78
0.49
0.85
1.08
SD
PPNC
8.68
7.07
6.76
6.47
7.54
8.44
6.58
9.25
6.69
9.50
10.33
11.47
9.64
11.51
9.64
10.64
SD
PPNC
Mean
11.09
6.63
6.35
5.43
5.76
6.64
6.15
7.96
6.48
6.53
7.44
4.20
7.54
4.75
8.28
10.30
CV
5.30
4.59
3.24
6.20
6.72
5.96
8.45
5.11
7.53
3.23
9.01
4.68
10.25
8.45
15.14
8.64
CV
144
R. PINHASI ET AL.
145
EVOLUTIONARY CHANGES IN THE MASTICATOR COMPLEX
TABLE 6. Linear regressions of mandibular dimensions over
time for the total set of specimens
Variable
N
r2
Slope
(mm/1000 years)
Sig.
F
RAMH
MAXL
RAMB
GONB
CONDB
ANTH
HM2_M1
ANTHIC
M2THIC
78
82
100
65
48
88
109
97
111
0.017
0.001
0.097
0.004
0.047
0.125
0.001
0.011
0.014
0.405
0.047
0.649
0.572
1.244
0.850
0.056
1.049
20.167
Ns
Ns
**
Ns
Ns
**
Ns
Ns
Ns
3.0
0.3
0.0
2.2
0.0
0.2
1.0
0.9
1.0
Slope values are in mm per 1000 years, Sig. indicates significant
slope values at * 5 P \ 0.05, and ** 5 P \ 0.01.
Fig. 4. Differences in CV values for mesiodistal and buccolingual dimensions of the dentition, by period.
Natufians have evenly distributed flat wear, while the
PPN populations have a more angled wear and the presence of cupped wear on occlusal surfaces. Similar
changes in wear pattern following the transition to agriculture were observed in Nubia (Smith, 1984), Japan
(Kasai and Kawamura, 2001) and other regions and are
believed to reflect a reduction in toughness of agricultural diets.
Therefore there is evidence for change in wear following change in mastication demands, which may be associated with the observed reduction pattern in some of
the mandibular dimensions and in the buccolingual
dimensions of most of the dentition. This fits well with
the ‘‘Masticatory-Functional Hypothesis’’ of Carlson and
Van Gerven (1977), which suggests that a decrease in
the functional demands placed on the masticatory complex among early agriculturalists lead to corresponding
alterations in the craniofacial complex. The change in
the size of the dentition is then viewed as a compensatory process following reduction in the anteroposterior
growth of the craniofacial complex. Since this study did
not involve the analysis of craniofacial dimensions, it is
not possible at this stage to ascertain whether the Levantine transition involved a similar trend. However,
previous craniometric analyses on much smaller Levantine samples shows that the Natufian’s vault and craniofacial architecture differ from the PPNB (Abu Hureyra)
sample. The Natufians had long vaults and a high and
narrow facial morphology while the Abu Hureyra
(PPNB) population had shorter and broader vaults, and
shorter faces (Pinhasi, 2004). Hence, the Natufian-Neolithic change in craniofacial and vault morphology is not
one of a simple reduction in overall size as predicted by
the IPDE model but rather suggests adaptation to a new
set of selective pressures (some of which are more than
likely relating to changes in diet).
Lack of change in caries rate may be the outcome of
SCE whereas dental reduction is counter-balanced by an
increasingly cariogenic diet as was noted in a diachronic
study of changes in dental dimensions among prehistoric
agricultural populations from the Valley of Oaxaca, Mexico (Christensen, 1998). In other words, lack of evidence
for an increase in caries is not by itself contra evidence
for selection for smaller dental dimensions but rather
the outcome of SCE. In the case of the southern Levantine populations, selection for smaller crown surface area
only affected the shortening of the buccolingual dimensions as a reduction in the mesiodistal dimension of crowns
would have led to change in the overall length of the dental arcades and a corresponding reduction in mandibular
and maxillary dimensions. Hence, the observed reduction
in buccolingual dimension and the retention of overall long
dental arches and robust mandibles can be viewed as part
of the overall compensatory balancing process.
The major limitation of the current study is its inability to assess the full array of morphological, pathological
and ontogenetic factors that may have been part of the
observed reduction pattern. For this reason, and to avoid
tautology, we focused on the assessment of our data in
relation to three models that explain post-Pleistocene
dental and mandibular reduction. Our results best fit
with the SCE model, which takes into account the synergy between selection for smaller dentition, which are
related to both changes in masticatory-functional demands and prevalence of oral pathology. However, our
results show that the SCE need not involve evidence for
overall mandibular size reduction particularly when the
dimensions that are being reduced are buccolingual. In
fact, a reduction trend in buccolingual dimensions will
achieve a reduction in the overall crown area (and hence
a reduced surface, which may be affected by caries),
while avoiding the shortening of the overall length of the
mandibular and maxillary dental arcades. The reduction
in the latter will follow a corresponding reduction in
overall mandibular dimensions, which will then result in
a masticatory apparatus that is no longer adapted for
the mastication of abrasive diet.
CONCLUSIONS
In this study, we analyzed diachronic trends in the
masticatory apparatus of late hunters and early farmers
from the southern Levant region. Temporal trends of
change in dental and mandibular dimensions were
examined using a series of linear regressions. Our results indicate a pronounced reduction trend that mainly
affected the buccolingual dimensions of the upper and
lower dentition. In total, 16 of the regression slopes are
American Journal of Physical Anthropology—DOI 10.1002/ajpa
146
R. PINHASI ET AL.
Fig. 5. Bivariate scatterplots of both significant (right column, A, C) and nonsignificant (left column, B) regression slopes of
change in mandibular dimensions over time (in uncalibrated radiocarbon years). [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com.].
significant; out of which seven are of the upper dentition
and nine of the lower dentition and only two are of
mesiodistal dimensions. The trend affected both Naturian
and Neolithic populations and hence appears to have
started prior to the period of initial crop domestication
(PPNA). The average reduction rate (slope value) for the
significant buccolingual dimensions and significant mesiodistal dimensions is 0.17 mm/1000 years. Interestingly,
the reduction in the buccolingual dimensions of the lower
dentition was not accompanied by a corresponding reduction in the overall dimensions of the mandible. Only the
anterior symphyseal height and the ramus breadth were
significantly reduced over time. Analysis of covariance
indicate that selection most likely acted only on the buccolingual dimensions resulting in overall decrease in
crown area but no overall decrease in dental arch length.
TABLE 7. Linear regressions of mandibular dimensions
over time for the total set of specimens excluding the
Pottery Neolithic group
Variable
N
r2
Slope
(mm/1000 years)
Sig.
RAMH
MAXL
RAMB
GONB
CONDB
ANTH
HM2_M1
ANTHIC
M2THIC
75
77
95
61
45
83
103
92
105
0.005
0.033
0.060
0.031
0.038
0.092
0.001
0.012
0.019
0.242
20.979
0.550
0.883
1.23
0.795
20.052
1.23
20.022
Ns
Ns
*
Ns
Ns
**
Ns
Ns
Ns
Slope values are in mm per 1000 years, Sig. indicates significant
slope values at * 5 P \ 0.05, and ** 5 P \ 0.01.
American Journal of Physical Anthropology—DOI 10.1002/ajpa
EVOLUTIONARY CHANGES IN THE MASTICATOR COMPLEX
Our results best fit with the ‘‘Masticatory-Functional
Hypothesis’’ of Carlson and Van Gerven (1977), which is
part of the SCE model (Calcagno, 1989). It suggests that
selective compromise may have affected the dental and
mandibular dimensions of the southern Levantine postPleistocene population in a manner that is not similar to
other post-Pleistocene trends (as it did not involve a
reduction in mandibular size). The fact that our study
focused on the earliest farming communities in the
region during a relatively short period of time in evolutionary terms, suggests that we may have discerned the
initial phase of a complex evolutionary process and
hence account for the difference between our results and
those reported from the above-discussed studies. Future
research will involve the assessment of wear patterns
in relation to changes in craniofacial and masticatory
complex and dental crowding to shed more light on this
process and its universalities.
ACKNOWLEDGMENTS
We thank Prof. Dani Nadel from Haifa University for
his kind permission to study some of the unpublished
PN material from the site of Tel Roim West (TRW),
Israel. Prof. Nigel Goring-Morris from the Hebrew University in Jerusalem gave permission to study some of
the unpublished PPNB specimens from the site of Kfar
HaHoresh, Israel. We also thank Simon Mays for reading and editing the manuscript and the anonymous
referees for their helpful comments.
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