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Discrete dental variations and biological distances of nubian populations.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 58:75-79 (1982)
Discrete Dental Variations and Biological
Distances of Nubian Populations
DAVID L E E GREENE
Department of Anthropology, university of Colorado, Boulder. Colorado 80309
KEY WORDS
Discrete dental variations, biological distance,
divergence, Smith-Grewal statistic, Nubia, Wadi Halfa, Kulubnarti
ABSTRACT
During the 1963-1964 field season, the University of Colorado’s
Nubian Expedition excavated a series of Meroitic, X-Group, and Christian
cemeteries from Wadi Halfa Sudan. Recently a joint expedition sponsored by the
Universities of Colorado and Kentucky excavated two additional Christian
cemeteries from Kulubnarti, some 80 miles south of Wadi Halfa. Earlier analysis
of discrete dental variations demonstrated that the Wadi Halfa populations did
not differ significantly from one another. Application of the Smith-Grewal multivariate measure of biological divergence, as modified by Sjovold, and Green and
Suchey, corroborates the original conclusion of biological stability and continuity
for the Wadi Halfa populations, as well as demonstrating that the Kulubnarti
populations are part of that pattern. None of the populations are significantly different from one another.
In 1979 the University of Colorado, in conjunction with the University of Kentucky, excavated two Christian cemeteries located near
the Medieval Christian stronghold of Kulubnarti, some 80 miles south of Wadi Halfa along
the Nile in the region of Nubia known as the
Batn-el-Hajr, or Belly of Stones (Van Gerven,
1981).Skeletons from these cemeteries (Table 1)
add to the population samples from Nubia
previously collected by the University of Colorado’s Nubian Expedition in the Wadi Halfa
region of the Sudan (Armelagos et al., 1965).
Analyses of the skeletal remains from the
Wadi Halfa region have contributed to the
understanding of the skeletal biology of Nubia
as well as addressing major questions in paleodemography, paleoepidemiology, paleopathology, microevolution, and population
relationships (e.g., Van Gerven et al., 1973;
Armelagos, 1969; Swedlund and Armelagos,
1969; Greene, 1973, 1981).
The majority of these investigations have
depended upon the proposition that there was
a considerable degree of genetic stability and
continuity in the Wadi Halfa area through the
sequential cultural phases labeled by archaeologists as Meroitic, X-Group, and Christian
periods. However, prior to the late 1960s most
0002-948318215801-0075$02.000 1982 ALAN R. LISS, INC.
specialists had argued that instead of genetic
stability and continuity, the area was, to the
contrary, characterized by major population
change brought about by the movement of the
X-Group people into the area as the preceding
Meroitic culture declined (Elliot-Smith and
Wood-Jones, 1910; Batrawi, 1935). The
X-Group people were thought to be more
Negroid than the Meroitics and thus introduced different genetic material through
hybridization with the remnant Meroitics.
Therefore, following this older perspective, one
would expect to find differences in the expression of traits with significant genetic components when contrasting Meroitics with
X-Group people or X-Group people with those
of the Christian era.
This older perspective, genetic change produced by major migration and hybridization,
was initially tested by Greene (1966, 1967a) in
his analysis of discrete dental morphological
traits from populations in the Wadi Halfa area.
Using a series of univariate comparisons, he
demonstrated that there were no significant
differences in the occurrences of 16 permanent
discrete dental morphological traits between
Received May 8. 1981. accepted September 28.1981.
76
D.L. GREENE
TABLE 1. Cemetery samples and their cultural affiliations
Area
Wadi Halfa
Cemetery
6-B-16
NAX
6-K-3
Affiliation
Meroitic
X-Group
Christian
Dates'
? - 350 AD
ca.
ca. 350- 550 AD
ca. 1050-1150 AD
Kulubnarti
21-$46
21-R-2
Christian
Christian
ca. 550- 750 AD
ca. 750-1450 AD
'Dates are for the approximate durations of the Meroitic and X-Group periods in the Wadi Halfa area (Greene. 1967a). The Christian cemetery
6-K-3 is dated following Adams (1967). The dates for the Kulubnarti cemeteries are from Van Gerven (1981).
the populations. From this, he concluded that
the Meroitic and X-Group populations are not
representatives of different racial groups, but
instead represent a continuum of successive
local Mendelian breeding populations in the
Wadi Halfa area (Greene, 1973, 1981).
Greene's conclusions were reaffirmed by Van
Gerven et al.'s (1976) discriminant function
and principle components analysis of cranial
metrics from the same Wadi Halfa populations. Also, other investigators such as
Nielson (1970), using different population
samples from Lower Nubia than those used by
Greene and Van Gerven et al., argue as well for
population continuity.
Some investigators, though, still argue for
discontinuity through racial displacement in
Lower Nubia (Strouhal, 1971; Strouhal and
Jungwirth, 1980). Thus the question of continuity versus discontinuity has not been completely resolved among those physical anthropologists working on skeletal materials from
Nubia. Consequently, the analysis of new
population data and a re-analysis of older data
using more powerful techniques will help
clarify the controversy.
The purpose of this paper is twofold. First, in
that a newer and potentially more powerful
multivariate method, the Smith-Grewal statistic (Grewal, 1962),than the series of univariate
comparisons originally used by Greene has
been developed and tested with considerable
success in assessing biological distance or
divergence of populations outside of Nubia, it
will be used to further test and corroborate
Greene's original conclusion that the Wadi
Halfa populations show a high degree of population stability and continuity. Second, the
Smith-Grewal statistic will also be used to
evaluate the degree of biological divergence
between the Wadi Halfa populations and the
new population samples from Kulubnarti,
some 80 miles to the south. How similar are
these populations? The answer to this question
will help determine the direction of further
research into the nature of biocultural evolution in Nubia. If the Kulubnarti populations
diverge significantly from the Wadi Halfa
populations, then researchers will have to
evaluate the potential effects of population
genetic differences on disease rates, mortality,
and microevolutionary process. On the other
hand, if the Kulubnarti populations do not
diverge significantly from those of Wadi Halfa,
then researchers will be able to assume genetic
stability and continuity, not only for the Wadi
Halfa area, but over a much larger area extending at least 80 miles further to the south.
METHODS
In 1967 Berry and Berry first applied the
Smith-Grewal statistic to the determination of
biological distance in human populations using discrete skeletal variants. Since that time
it has been widely used as a non-metrical multivariate measure of distance. Most applications
in physical anthropology have focused upon
cranial variations (Finnegan and Cooprider,
1978),though at least one has utilized discrete
morphological variants in the dentition (Berry,
1976).
Sjgvold in 1973 reviewed the applicability of
the Smith-Grewal statistic and further developed its theoretical rationale. Green and
Suchey, in 1976, added additional theoretical
understanding, and in particular demonstrated that the Freeman-Tukey transformation should be used to stabilize variances
in small samples.
Consequently in this study, each discrete
trait frequency of occurrence was transformed
using
8 = %sin-'(l -2k/(n+1))
+ ?hsin-'(l-2(k+l)/(n+l)),
where k equals the occurrence of a trait and
n equals the total number of observations.
Mean measures of divergence (or distance)
were then found:
77
BIOLOGICAL DISTANCES OF NUBIAN POPULATIONS
where r equals the number of pairs of traits
considered, Oli is transformed frequency of the
ith trait in the first population, nIi the total
number of observations for the ith trait in the
first population, O,, the transformed frequency
of the ith trait in the second population,
and nZithe total number of observations for
the ith trait in the second population. The
variance of a mean measure of divergence then
equals:
and the standard deviation equals the square
root of the variance.
The statistic D and its variance are based
upon the assumption of statistical independence between all traits considered (Sjqvold,
1973). care must be taken when considering
discrete traits which are bilaterally expressed
to control for the potential confounding effects
of symmetrical or asymmetrical expression
(Sjqvold, 1973; Greene, 1967b). If there are
significantly different expressions of a trait
between the sexes in a population, then sexspecific comparisons should be made in calculating D. Otherwise the frequencies can be
combined.
In the earlier study of the Wadi Halfa populations (Greene 1967a), 16 dental traits were
found to be statistically independent of one
another, not significantly asymmetrical in
bilateral expression, and not significantly different in distribution by sex. Due to small sample sizes, it is not possible to determine
whether or not the same pattern of bilateral
symmetry and the lack of differential expression by sex prevails in the Kulubnarti populations. Furthermore, even though some vari-
ants are individually observable in fairly large
numbers (Table 2), due to tooth loss and heavy
wear the number of cases showing the simultaneous Occurrence of several different traits is
not large enough to test statistically for independence. However, for purposes of this paper,
it is assumed that the Wadi Halfa pattern of
statistical independence, bilateral symmetry,
and no difference in expression by sex also
prevails in the Kulubnarti populations.
Not all of the original 16 traits are appropriate for the current analysis. In the earlier
study, all teeth were extracted and direct
observations were made on molar root fusions
and third molar agenesis as well as maxillary
premolar root fusions. Similar extractions are
not feasible at the current time for the Kulubnarti samples; and even if they were, there is
some doubt that root fusions in particular can
be scored objectively as discrete variations in a
way comparable to the categories used in the
earlier study since fusions do vary in a continuous way. The loss of third molar agenesis information is probably not serious in that even
when it was used in the original study it added
very little to the crude measure of distance
then used.
In addition, even though the same investigator (Greene ) made all of the observations in
the Wadi Halfa and Kulubnarti samples, experience has shown that mandibular molar
fissure patterns are most difficult to score consistently and therefore have been eliminated.
Berry (1976), in comparing fissure observations made by different observers, came to the
same conclusion.
Cusp number on the first maxillary molars
was not used since almost all of the Nubian
populations have four cusps at frequencies
near 100%. Therefore, this would have added
little discriminatory power to the D estimates.
Finally, for some of the traits that were in
the early study categorized into more than present or absent classes, the finer categories
were combined as present. Doing this, as well
TABLE 2. Trait frequencies and Freeman-Tukey tramformations
NAX
6-B-16
1)
2)
3)
4)
5)
6)
7)
Wn
11/48
36157
28/36
32/36
41/48
16/34
22/48
e
0.5660
-0.2616
-0.5675
-0.8314
-0.7511
0.0572
0.0817
Wn
19/64
42163
38/47
29137
52161
29/44
24142
6-K-3
8
0.4108
-0.3341
-0.6417
-0.5814
-0.7914
-0.3163
-0.1401
Wn
20148
14/28
10113
58161
24131
8/18
43/62
2 1-S-46
8
0.1631
0.0000
-0.5224
-1.0083
-0.5568
0.1056
-0.3903
Wn
26/52
14/24
13/15
38/38
17/17
317
10121
8
0.0000
-0.1608
-0.7442
-1.1364
-1.0929
0.1263
0.0455
21-R-2
Wn
21/58
32149
34139
34/37
20124
9117
10126
8
0.2746
-0.3045
-0.7905
-0.9096
-0.6851
-0.0557
0.2242
78
D.L. GREENE
TABLE 3. Distances (0)
6-B-16
6-B-16
NAX
-0.0028
(0.0236)
NAX
6-K-3
6-K-3
0.0155
(0.1103)
21-S46
0.0574
(0.0466)
21-R-2
-0.0299
(0.0307)
0.0212
(0.0311)
0.0108
(0.0447)
0.0061
(0.0291)
-0.0053
(0.0054)
0.0192
(0.0388)
-0.0422
(0.05941
21-546
21-R-2
Standard deviations are in parentheses.
as making the observations between Wadi
Halfa and Kulubnarti more readily comparable, also insures the independence of the
traits. Otherwise, for example, if maxillary second molars were scored as 4, 4 -, 3 + , or 3,
then several, depending upon views of degrees
of freedom, statistically dependent variables
would be included in D; pesence or absence of
4, presence or absence of 4 - , presence or
absence of 3 + , and presence or absence of 3.
Therefore, the traits used in the present
study are as follows: 1)Carabelli’s Trait on
Maxillary First Molar: Cusp, pit, and groove
combined as present. Genetic studies indicate
that cusps, pits, and grooves may be variable
manifestations of the same genotype (Kraus,
1951; Tsuji, 1958).This is further supported in
Nubian populations by bilateral concordance
studies (Greene, 1967a).2) Four cusps on Maxillary Second Molar: The 4 and 4- categories
used in the earlier study are combined since the
distinction between the two can be obscured
by relative tooth size (Greene, 1967a).3) Three
cusps on Maxillary Third Molar: Both 3 and
3 categories scored as present. Occasionally
3 + + teeth (Greene, 1967a) occur here. The
supernumerary cuspule in this type may be the
metaconule recently reintroduced into the
literature by Harris and Bailit (1980). 4) Five
cusps on Mandibular First Molar: This also includes a very small number of six cusped
molars (C6or C7).5) Four cusps on Mandibular
Second Molar. 6) Four cusps on Mandibular
Third Molar. 7)Shoveling on Central Maxillary Incisors: Hrdlicka’s trace or moderate
shoveling are combined. Shoveling in Nubian
populations rarely exceeds these levels. If central incisors were missing and lateral incisors
could be observed, then the shoveling trait
manifestation on the laterals was used for this
observation, since the shoveling field in the incisors always produces shoveling in the later-
+
als if it exits in the centrals (Carbonell, 1963;
Greene, 1967a).
When both right and left teeth were present
and observable, observations were made from
the left teeth. When only one or the other was
present and observable, it was used. Data from
both sexes were combined. All observations
were made on permanent teeth. And, finally,
observations were restricted to those teeth
with minimum wear, no greater than Brothwell’s Stage 3 (Brothwell, 1963).
RESULTS
The three largest cemetery samples from the
Wadi Halfa area (6-B-16,NAX, and 6-K-3)were
used in the earlier study to evaluate biological
distance and are used here to confirm the
results of that earlier study and to compare
with the recently excavated cemetery samples
from Kulubnarti (214-46 and 21-R-2).)
As Sjqivold (1973) points out, the SmithGrewel measure of biological divergence (or
distance) is a multivariate statistic that tests
the hypothesis that the difference between two
populations is no greater than zero. Consequently, D values can be negative as well as
positive (Table 3). If the absolute value of a D
value exceeds twice its standard deviation,
then the difference is statistically significant
at least at the 0.05 level (SjBvold, 1973).When
the Freeman-Tukey transformation is used to
calculate 0 as in this analysis, then if the D
value exceeds twice its standard deviation the
difference is statistically significant at somewhere between 0.05 and 0.03 (Green and
Suchey, 1976).
All of the D values are extremely low and
none are even close to being significant.
DISCUSSION
Prior to Greene’s analysis of the Wadi Halfa
populations, many archaeologists and physical
BIOLOGICAL DISTANCES OF NUBIAN POPULATIONS
anthropologists believed that the transition
from the Meroitic cultural phase to the
X-Group in Nubia was accompanied by a major
infusion of people who were biologically different from the Meroitic people. Indeed, some
(i.e. Strouhal, 1971)continue to argue that the
X-Group people are far more negroid than are
the Meroitics. On the other hand, none of the
recent proponents of that opinion have incorporated the Wadi Halfa populations, or those
from Kulubnarti, into their analysis, nor have
their population samples been incorporated in
this study. It is possible, however, that there
may have been some infusion of more Negroid
peoples into other parts of Nubia during the
X-Group period.
The present analysis does clearly corroborate the earlier study of the Wadi Halfa populations and, furthermore, demonstrates that the
pattern of biological stability and continuity
extends from Wadi Halfa to Kulubnarti. In
this area of Nubia there is no evidence for the
infusion of people with radically different
biological backgrounds during the X-Group
period.
ACKNOWLEDGMENTS
Research support for this paper was made
possible by National Science Foundation grant
no. BNS-78-00255,Co-principle Investigators
W.Y. Adams, D.L. Greene, and D.P. Van
Gerven.
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