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Diachronic variation in cranial thickness of near eastern populations.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 62127-133 (1985)
Diachronic Variation in Cranial Thickness of Near Eastern
Populations
PATRICIA SMITH, YOHANAN WAX, ADRIAN BECKER, AND
SHMUL EINY
Departments of Orthodontics (A.B.1 and Anatomy (PS., S. E.), Hadassah
School ofDentaZ Medicine, Department of Statistics iY. W.),Hebrew
University, Jerusalem, Israel
KEY WORDS
Near East, Cephalometrics, Cranial thickness,
Diachronic change
ABSTRACT
Cephalometric radiographs were taken of 111 skulls of skeletal remains of populations living in Israel and Jordan during the last 12,000
years. From these radiographs, skull length and height, and cranial thickness
were measured. For each sex and period, high correlations were found between
cranial thickness at vertex, bregma, and lambda. Cranial thickness at nasion
was correlated with sinus width but not sinus height. All measurements were
correlated with skull length but not skull breadth. Using multivariate analysis, no significant differences in cranial thickness were found between the
sexes. Significant diachronic trends were found in lambda and sinus width,
and they were independent of variation in skull length.
The Near East, with its long history of
agriculture and pastoralism (Bar-Yosef,
19841, is a good region in which to examine
the long-term effects of such adaptations on
the human physique. Studies carried out on
skeletal and dental morphology of Holocene
populations have shown little evidence of unidirectional change in these parameters, but
rather a series of fluctuations that have been
interpreted as reflecting secular change and
population replacement (HrdliEka, 1938; Arensberg, 1973; Ferembach, 1973; Smith et
al., 1984). However, in a radiographic study,
Smith et al. (1984) did find evidence of diachronic change in humeral cortical thickness
over the last 12,000 years. We have accordingly begun investigating the total extent of
variation in bone mass. In this report we
present the findings of a radiographic study
of cranial thickness in skulls of specimens
ranging from the terminal Pleistocene
(10,500 B.C.E.’) to recent (1,800 C.E.).
In addition to chronological factors, a number of other variables have been associated
with cranial thickness. Studies have been
carried out both from direct measurement of
skulls and cephalometric radiographs, the
latter taken both of the living and of dry
skulls. Such studies have shown significant
0 1985 ALAN R. LISS, INC.
interpopulation variation not only in overall
thickness, but also in relative thickness of
frontal, parietal, and occipital bones. Adeloye et al. (1975) postulated that cranial
growth patterns, as well as liability t o haemoglobinopathies affecting diploic width-especially of the parietals, might contribute to
the differences observed. Brown et al. (1979)
suggested that cranial thickness was associated with general skeletal robusticity, a hypothesis borne out by comparisons made by
them, both of Australian crania of different
periods and of Australian Aborigine and
Caucasian populations. It has also been postulated that cranial thickness may be inversely related to cranial capacity (Todd,
1924)or to variation in piezoelectric currents
associated with differences in the direction
and intensity of magnetic fields operating on
the earth’s surface a t different periods (Ivanhoe, 1979).
In addition t o investigating population differences, a number of studies have been carried out on age-related changes in cranial
thickness of the adult skull (Adeloye et al.,
1975; Baer, 1956; Baer and Harris, 1969;
Received July 15, 1983; revised March 26, 1984; accepted January 14,1985.
’B.C.E., Before Christian Era; C.E., Christian Era.
128
P. SMITH, Y.WAX, A. BECKER, AND S. EINY
Hansman, 1966; Hellman, 1927; Israel, 1968,
1973; Tallgren, 1974). However, in two of the
few longitudinal studies that have been carried out (Israel, 1968, 1973; Tallgren, 1974),
conflicting conclusions were reached. Israel
(1968) found a n overall increase of 5-6% in
most dimensions measured, while Tallgren
(1974) found no such changes.
Since the available archaeological and anthropological evidence suggests several
waves of population replacement in the Near
East during the Holocene, any discussion of
diachronic change in this region must include some measure of population differences
as distinct from chronological sequence. In
the present study we have attempted this
through the incorporation of length and
height measurements of the skull into the
analysis. We have also grouped the specimens by biological age, as well as chronological sequence and sex, in order to test for the
effects of these variables.
Fig. 1. Tracing of cephalometric roentgenograph with
lines constructed for measurement.
MATERIALS AND METHODS
Cephalometric roentgenographs were
taken of 111skulls of skeletal remains excavated from a number of sites in Israel and
Jordan. They were identified by period as
follows: recent Bedouin, 1800 c.E.; Early
Arab, 800-1500 c.E.; Late Hellenistic to Byzantine, 100 B.C.E.-400 c.E.; Middle Bronze
Age, 2,200-1,550 B.c.E.; and Natufian, 10508500 B.C.E.
For each individual, age and sex determinations were made from the entire skeleton,
where present (after Krogman, 1962). Lateral cephalographic roentgenographs were
then taken of the skulls, using a specially
designed cephalostat, such that the cranium
was inverted, as described by Brown (1973).
To reduce differences in magnification of
midline structure, the focus to midsagittal
distance was fixed for each specimen a t 180
cm, and the midsagittal to cassette distance
a t 15 cm. In addition a scale was suspended
parallel to and opposite the midsagittal plane
of each specimen and used to determine the
magnification of midline structures on the
roentgenograph.
The roentgenographs so obtained were
placed on a viewing box and covered with
acetate paper. The skull was then traced onto
the paper. In addition to anatomical landmarks, a number of constructed lines and
angles were added to the tracing (Fig. 1). At
bregma a line was drawn from the outer table of the skull, a t right angles to the Frank-
fort plane. This line was used to measure
skull height and cranial thickness a t vertex.
Finally, maximum anterior-posterior length
of the skull was measured along a line drawn
parallel to the Frankfort plane.
For the frontal sinus, maximum height and
depth measurements were taken at right angles to one another, such that they incorporated the maximum superior-inferior and
anterior-posterior dimensions of the sinuses
(Fig. 2). All data were transferred to the computer. The measurements were corrected for
magnification, so that analysis was carried
out on corrected values. All measurements
were taken by one observer, using Vernier
calipers accurate to 0.1 mm, and the magnification was recorded from the scale, as projected on the film.
Scattergrams and Pearson correlation coefficients were used to assess the relationship
between the various cranial thickness parameters and between them and the corresponding length and height of the skull. The
relationships were examined separately for
each sex and age subpopulation in each period. Period differences in the seven cranial
thickness measurements controlled for the
effects of the confounding factors; sex, age,
and skull length and height were estimated
through the use of Multivariate Analysis of
Covariance (MANCOVA) models (Hull and
Nie, 1981).These models included period and
sex factors, their interaction, and the covar-
DIACHRONIC CHANGE IN CRANIAL THICKNESS
919
3 i N
A
B
129
I I I I I I I I
C
Fig. 2. Tracing of sinus outline to show variations
and planes of measurement.
iants-age (as a dichotomous variable),
length-height, and sex-length. The goodness
of fit of the model was examined by comparing the observed means of the cranial thickness measurements in period and sex
subclass to the predicted means under the
model.
The significance of cranial thickness
changes through time was assessed using the
Roy union intersection test. Univariate analysis of the covariance model was used to test
the significance of the changes through time
in each of the cranial thickness characteristics. All analyses were performed using the
SPSS-MANCOVA program, after Hull and
Nie (1981).
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d M e i i i 3 -
RESULTS
The Natufian skulls were fragmentary,
limiting the number of valid measurements
that could be carried out on them. They were
therefore omitted from the statistical
analysis.
Mean values for males were higher than
those of females (Table 1)and increased with
age (Table 2). Cranial thickness parameters
showed positive, and on the average higher,
correlation among males than among females (Table 3). The highest correlations
found were between vertex and bregma (0.8
males, 0.68 females), and both were positively correlated with lambda (0.57 males,
0.32 and 0.36 females). A similar pattern applied to male-female values for each period
studied, but Box's M-test for homogeneity of
dispersion matrices revealed no significant
differences (p = 0.15) between the dispersion
matrices in period-sex subclasses. The correlation between skull length and cranial
thickness was also fairly high but not that
between skull height and cranial thickness.
o o r n o o m o o
mmNmmNmm
130
P. SMITH, Y.WAX, A. BECKER, AND S. EINY
TABLE 2. Mean values and standard deuiation for skulls of differentperiods (sexes combined)
S.D
No
X
S.D
No.
X
S.D
No
Middle
Bronze
X
1.6
1.5
1.0
4.7
2.4
3.4
8.7
5.6
24
24
23
23
23
24
24
24
7.6
5.8
5.9
20.4
7.3
12.1
176.1
115.0
1.2
1.5
1.2
5.6
2.0
2.9
7.7
5.1
15
15
15
15
15
15
15
15
6.5
5.6
5.5
23.3
9.8
14.3
174.1
113.4
1.7
2.1
2.1
5.4
2.6
2.7
9.8
5.7
14
14
14
12
12
13
14
11
6.8
5.8
6.1
22.2
9.2
13.1
181.8
113.0
1.6
1.2
1.1
5.6
2.5
2.7
7.6
3.7
2.5
2.7
1.0
6.5
1.2
1.8
3.7
4.7
12
12
12
12
12
12
12
12
8.7
6.3
6.5
23.5
9.7
14.8
179.7
116.7
0.9
0.8
1.3
6.3
2.5
4.8
7.0
6.4
9
9
9
9
9
9
9
9
7.2
5.1
5.0
25.4
10.3
14.7
176.6
113.1
1.8
1.2
1.3
6.0
2.5
4.0
8.6
4.7
2
2
7.3
8.2
7.9
27.2
10.0
11.7
183.4
135.5
1.7
3.5
3.7
5.3
1.2
1.7
11.3
53
Bedouin
Parameter
No
X
Age group 15-49
Lambda
19
7.9
5.6
Vertex
19
19
Bregma
6.0
18
Sinus height
20.5
Sinus width
18
7.9
19
Nasion
11.4
19
Length
178.6
19
Height
114.9
Age group 50 +
Lambda
3
8.3
3
Vertex
6.0
Bregma
3
5.6
Sinus height
3
16.1
3
Sinus width
6.3
3
Nasion
12.7
3
Length
183.6
Height
3
116.3
-
HellenisticByzantine
Early Arab
~~
~~
2
2
2
2
2
2
S.D
TABLE 3. Pearson correlation coefficients between skull characteristics
males (aboue diagonal) and females (below diagonal)
Lambda
Vertex
Bregma
Sinus height
Sinus width
Nasion
Length
Height
Lambda
Vertex
Bregma
-
0.57
0.57
0.80
0.32
0.36
0.19
0.02
0.04
0.16
0.02
I
0.68
0.06
0.23
-0.22
0.42
0.06
0.07
0.10
-0.04
0.49
0.05
This was particularly true for males. In view
of these findings, length, and its interaction
with sex, were introduced as covariants in
subsequent analyses. In view of the slight
differences found between younger and older
age groups, age was also incorporated as a
covariant in the multivariate model.
Table 4 shows the results of the covariance
model, with cranial thickness as the dependent variable, period and sex as grouping
factors, and covariates as previously defined.
As the significance levels show, only period
showed a significant effect (p = 0.007), and
there was no significant interaction between
sex and period. Values obtained for individual parameters are shown in Table 5. Significant differences over time were found only
for lambda and sinus width. The observed,
expected, and adjusted means calculated for
these two variables are shown in Figure 3,
with the multiple comparison taken into ac-
Sinus
Ht
Sinus
Wdth
0.18
0.14
0.17
0.32
0.32
0.27
0.67
0.50
0.27
-0.07
-0.03
0.25
0.09
0.14
Nasion
Length
Height
0.39
0.28
0.24
0.46
0.71
-
0.41
0.40
0.36
0.17
0.27
0.29
-0.05
-0.14
0.28
0.23
0.26
-0.01
0.02
0.08
0.34
0.43
-
-
TABLE 4. Multivariate significance tests for overall
differences in cranial thickness parameters among the
factor levels
Factor
Period
Sex
Period bv sex interaction
p-value for Roy test
0.007
0.97
0.19
count. The small differences between observed and expected means demonstrates the
validity of the model used. The adjusted
means for lambda increased while those for
sinus width decreased. Major significant differences were present between the two more
recent groups (Bedouin and Arab) and the
two earlier groups (Hellenistic and Bronze
Age). Although male and female adjusted
values for lambda width were widely separated, no significant differences were present
(p = 0.5).
131
DIACHRONIC CHANGE IN CRANIAL THICKNESS
isticByzantine skulls, and one Middle Bronze
Age skull fell into this category. They included females and both young and old individuals in whom cranial thickness at vertex
ranged between 7.4 and 9.4mm. In no instance was any pathological lesion such as
Paget's disease or haemoglobinopathies
identified.
The Natufian skulls were larger than all
others measured, and thicker at vertex and
bregma (Table 1).They resembled the Middle
Bronze crania most closely.
TABLE 5. Llniuariate F-test' for differences over time
F
D-value
4.59
0.86
1.27
1.59
4.58
2.02
0.005
0.47
0.29
0.20
0.005
0.12
Parameter
Lambda
Vertex
Bregma
Sinus height
Sinus width
Nasion
'With (3.81)degrees of freedom.
Cranial thickness at vertex and bregma,
while not showing statistically significant
differences between periods, was thicker in
the earlier, Middle Bronze Age sample than
in other samples studied. This was so despite
the fact that a relatively larger percentage of
Early Arab skulls had exceptionally thick
cranial bones. Ten skulls were exceptionally
thick, with cranial thickness at vertex more
than one standard deviation greater than the
mean value of the total sample. Seven Early
Arab skulls, two Bedouin skulls, two Hellen-
DISCUSSION
The high correlation found between the
variables studied here demonstrates the importance of a multivariate approach to the
analysis of diachronic trends. However, such
studies are frequently subject to limitations
imposed by sample sizes. In the present study
this restricted the number of age categories
used. In order to best control for age effects,
tests were carried out twice, once using ages
SINUS Y I D T H
10-
9B-
I
7-
8
6-
w
A
.d
54-
w
d
.*
3-
2-
8
1-
8
0
I
I
I
LWBDA
ld9B-
x
?65-
o
A
.
4
x
m
m
A
*
b
o
4-
L
32-
15
O
A
I
X
Ii
"I
I
0
D
x
L
0
I
I
57
69
Fig. 3. Observed, expected, and adjusted values for
mean values of lambda and frontal sinus width. Horizontal axis = measurements in mmx 10; vertical axis =
group, where 1,3,5,
,7 represent males of increasing age
from Bedouin to Middle Bronze and 2, 4, 6, 8 represent
81
93
Lm
females ranked from Bedouin to Middle Bronze; open
triangles = adjusted values; open squares = observed
values; crosses = expected values; closed squares = superimposition of observed and expected values.
132
P. SMITH, Y. WAX, A. BECKER, AND S. EINY
15-39 and 40+ and once using ages 15-49
and 50+. The results obtained were similar
for both age groupings and not significant.
Our findings regarding the lack of statistically significant sex differences in cranial
thickness a t any location other than nasion,
on uncorrected data agree with those of
Brown et al. (1974) on Australian Aborigines
and Adeloye et al. (1975) on North American
whites and blacks. In our study, as in the
study by Brown et al. (1979) a tendency was
found for female values to be smaller than
those of males, although Adeloye et al. reported a tendency for increased frontal bone
thickness in older females. This is a n interesting finding in view of the dimorphism
shown by all the groups studied here, in
length and height of the skull. It is also interesting to note that sex differences in the
development of muscle markings in the nuchal crest region (Krogman, 1962) are not
reflected in cranial thickness at lambda. The
pronounced interaction shown between skull
length and thickness of cranial bones further
suggests that shorter skulls are relatively
thicker.
Age-related changes in cranial thickness
were similarly insignificant in our samples.
While this study was, by necessity, a crosssectional study, reference to other studies
supports the hypothesis that thickness of cranial bones shows little correlation with age.
Todd (1924) and Adeloye et al. (1975) both
found age-related oscillations in cross-sectional samples studied by them. Todd’s study,
like ours, was based on dry skulls, while
Adeloye et al. measured cephalographs taken
of living individuals. The longitudinal studies, by Israel et al. (1968, 1973) and Tallgren
(1974), yielded conflicting results. This may
be related to differences in the age groups
selected by them for study. All of Israel’s
subjects were younger than 56 years, at the
time of the second phase of the longitudinal
study, while Tallgren’s (1974) subjects COVered a wider (20-73 years) age range.
As expected from reference to published
studies on the skeletal morphology of Near
Eastern populations (Arensberg, 1973; Ferembach, 1976; Smith et al., 19841, the Bronze
Age to recent populations showed fluctuations in skull length and height ratios
suggestive of population replacement rather
than unidirectional trends. Diachronic
changes were present a t lambda and in sinus
width. Cranial thickness a t lambda was
thickest in the two most recent groups and
was independent of skull length, while sinus
width was greatest in the two earliest groups.
However, a marked difference in cranial
thickness at vertex and bregma and in sinus
size was also found between the Natufian
and all later groups. A tendency was found
for the Middle Bronze Age group to approach
the Natufians most closely in these parameters.
Comparison with populations studied elsewhere is limited because of differences in
measurement techniques used. Israel (1968,
19731, Tallgren (19741, and Adeloye et al.
(1975) used constructed landmarks rather
than anatomical ones, as used here, and/or
failed to correct for radiographic enlargement, which averages 6-8% for midline
structures using conventional cephalometric
techniques. Cranial thickness at lambda,
vertex, and bregma in Near Eastern Middle
Bronze and later periods lie well within the
range of variation of modern European and
North American Caucasians, and is thinner
than that of North American blacks or Australian Aborigines.
Nasion is relatively thick in our samples,
and the frontal sinus is large. This appears
to be a characteristic of recent Caucasians as
compared with other population groups.
ACKNOWLEDGMENTS
This work was supported by a grant from
the Israel Academy of Sciences. Part of this
study is based on work carried out by S. Einy
in partial fulfillment of the D.M.D. requirements of the Hebrew University.
The authors would like to thank Y. Ainan
for carrying out data analysis, J. Berkowitz
for her painstaking work with the illustrations, and Hannah Siegal for coping with the
typing and numerous tables.
We are particularly grateful to an anonymous reviewer for his constructive and detailed advice during the review stage of this
work.
LITERATURE CITED
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Tel Aviv.
Baer, M J (1956) Dimensional changes in the human
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Baer, MJ, and Harris, JE (1969) A commentary on the
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Bar Yosef, 0 (1984) The Mediterranean Levantine EpiPaleolithic as the background to the Neolithic Revolution. In P Sorenson and P Mortensen (ed):The Origins
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skeleton. Arch. Oral. Biol. 13:133-137.
Israel, H (1973)The dichotomous pattern of craniofacial
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Ivanhoe, F (1979)Direct correlation of human skull vault
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Smith, P, Bar Yosef, 0, and Sillen, A (1984)Archeological and skeletal evidence for dietary change during the
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Cochen and G Armelagos (eds): Paleopathology and
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Tallgren, A (1974)Neurocranial morphology and aging:
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