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BRIEF COMMUNICATION
Northern exposure: Mandibular torus in the Greenlandic Norse
and the whole wide world
G. Richard Scott
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Roman Schomberg
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Victoria Swenson
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Donovan Adams
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Marin A. Pilloud
Department of Anthropology/MS 0096,
University of Nevada Reno, Reno, NV
89557
Correspondence
G. Richard Scott, Department of
Anthropology/MS 0096, University of
Nevada Reno, Reno NV 89557
Email: grscott@unr.edu
Abstract
Objectives: In the first issue of the American Journal of Physical Anthropology, E.A. Hooton noted
the expression of Eskimoid characteristics in the Icelandic skull, one of which was mandibular
torus. Our goal is to evaluate this trait in another North Atlantic population, the Greenlandic
Norse.
Materials and methods: An investigation of mandibular torus was carried out on all Greenlandic
Norse skeletons disinterred up to 1986 (n5109), along with comparative samples from Iceland
(n582), Norway (n598), and Denmark (n564). Torus expression was scored on a six grade scale
with absence and five degrees of trait presence.
Results: Greenlanders and Icelanders show extraordinarily high frequencies (65–97%) and pro-
nounced expressions of mandibular torus. More surprising was the almost complete absence of
this trait in a Danish Viking sample (9%) and a significantly lower frequency in medieval Norwe-
gians (48%).
Discussion: The dramatic expression of mandibular torus in the Greenlandic Norse and their con-
trast to related Scandinavian populations in Europe stimulated the collection of data from the
literature and the database of Christy G. Turner II for 49,970 individuals in 335 populations. When
plotted on a global scale, mandibular torus shows a strong clinal distribution with the highest fre-
quencies in northern latitudes and the lowest frequencies around the equator. Although
mandibular torus has some hereditary component, as indicated by family studies, the trait has a
strong environmental component of variance. How factors of a northern environment, including
climatic stress and dietary behavior, influence torus expression remains enigmatic.
1
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INTRODUCTION
The Norse colonized Greenland from Iceland in A.D. 986. During their
500 year occupancy of the island, the Norse exhibited a number of
temporal trends, including decreases in tooth, brain, and body size and
an increase in third molar agenesis (Scott, Halffman, & Pedersen,
1992). Another trait that exhibits an interesting pattern of variation is
mandibular torus, a bony growth on the lingual side of the mandible.
Mandibular torus has long been known to be common among northern
groups, especially Eskimos, Aleuts, and Lapps (Hrdlička, 1940; Moor-
rees, 1957; Oschinsky, 1964; Schreiner, 1935). None, however, exhibit
this torus to such a degree as the Greenlanders (Scott, Halffman, &
Pedersen, 1992; Sellevold, 1980).
Researchers have long debated the etiology of mandibular tori.
The higher frequencies in Asians compared to Europeans (Jainkittivong
& Langlais, 2000) led some to argue the trait is heritable (Carson, 2006;
Sawyer, Allison, Elzay, & Rezzia, 1979). Even granted this pattern of
variation, there is disagreement as to how genes contribute to the
development of these bony exostoses. Early studies described the
mode of inheritance as either autosomal dominant or autosomal reces-
sive (Alvesalo & Kari, 1972; Johnson, Gorlin, & Anderson, 1965; Krahl,
1949; Suzuki & Sakai, 1960). Some studies suggest mandibular torus is
inherited as a monoallelic trait with complete or partial penetrance, an
explanation utilized when patterns of segregation are not consistent
with simple Mendelian models (e.g., Gould, 1964). Moorrees, Osborne,
and Wilde (1952) suggested three independent loci control tori
American Journal of Physical Anthropology 2016; 00: 00-00 wileyonlinelibrary.com/journal/ajpa V
C2016 Wiley Periodicals, Inc.
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1
Received: 29 April 2016
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Revised: 20 June 2016
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Accepted: 1 July 2016
DOI 10.1002/ajpa.23053
expression. In a recent study, researchers found 93.6% of monozygotic
twins were concordant for mandibular torus expression. Dizygotic
twins, by contrast, had a concordance rate of 79.4% (Au
skalnis et al.,
2015). The most parsimonious interpretation holds that mandibular
torus is a threshold trait with a polygenic mode of inheritance. Despite
disagreement on mode of inheritance, family and twin studies nonethe-
less indicate heredity plays some role in mandibular torus development.
Several environmental causes have been proposed to explain the
presence and variation in mandibular torus. Eggen (1989) examined
individuals with mandibular torus in two categories: those who brux
and those who do not. From this comparison, he estimated that 30%
of mandibular torus expression is dictated by genes with the remaining
70% reflecting environmental factors (e.g., occlusal stress). Occlusal
stress and parafunctional activity may be important components of the
production of these exostoses (Hassett, 2006; Igarashi, 2016; Johnson,
1959; Kerdpon & Sirirungrojying, 1999; Pechenkina & Benfer, 2002).
Mayhall (1970) and Eggen and Natvig (1991) suggest a coarse diet pro-
motes the development of mandibular torus. Eggen (1993) also pro-
posed that a marine diet with high levels of omega-3 fatty acids and
vitamin D might promote excessive bone growth with a possible influ-
ence on unusually large mandibular and palatine tori. This idea was
tested by Baumann, Lynnerup, and Scott (in press) who examined the
relationship between torus expression and stable carbon and nitrogen
isotope compositions in Greenlandic Inuit and Norse. For the most
part, these authors found no significant association between stable iso-
topes and torus. The only statistically significant finding was an inverse
relationship between mandibular torus expression and stable nitrogen
isotope levels in the Inuit (but not the Norse).
Mandibular torus is uncommon in young individuals although rela-
tively high frequencies have been reported for Lapp and Aleut children
(Moorrees, Osborne, and Wilde, 1952). Haugen (1992) found a larger
number of individuals with mandibular torus in the 35- to 65-year-age
group. Jainkittivong and Langlais (2000) identified a statistically signifi-
cant prevalence that increases with age in a Thai sample. Topazian and
Mullen (1977) suggest those with a predisposition for mandibular torus
exhibit continuous growth of this exostosis throughout life. Other
researchers have found it becoming more pronounced over the course
of an individual’s lifetime relative to specific climatic, dietary, and life-
style factors (Axelsson & Hedegård, 1981; Eggen, 1989; Hrdlička,
1940; Ihunwo & Phukubye, 2006; Jainkittivong & Langlais, 2000;
Pechenkina & Benfer, 2002). This suggests that while mandibular torus
is heritable, environmental factors such as masticatory stress influence
the degree to which tori are expressed (Carson, 2006; Moorrees,
Osborne, and Wilde, 1952).
There is disagreement among researchers regarding sex differences
in mandibular torus. Some have found no sex differences in torus expres-
sion while others report higher frequencies in either males or females.
No consistent pattern has emerged across dozens of studies and hun-
dreds of samples. This contrasts with palatine torus, which shows a con-
sistent bias in favor of females (Halffman, Scott, & Pedersen, 1992).
Our goal is to evaluate the geographic and temporal variation of
mandibular torus among Norse populations in the North Atlantic, with
a focus on Greenlanders. Additionally, we want to determine how the
pattern of torus variation among Europeans in this part of the world
compares to populations in every environmental setting imaginable,
from the Arctic to subarctic, temperate deciduous forests, grasslands,
tropical rainforests, deserts, and Pacific islands. Excluding Antarctica,
every continent is sampled.
2
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MATERIALS
All Greenlandic Norse skeletons excavated up to 1986 were examined
in this study. The Eastern settlement sites of Herjolfnes and Gardar
along with the Western settlement sites of Sandnes and Anavik were
excavated by P. Nørlund and A. Roussel between 1921 and 1932
(Nørlund, 1924, 1929; Roussell, 1936, 1941). The Benedictine Convent
of the Eastern settlement was excavated by C.L. Vebæk from 1945 to
1948 (Vebæk, 1956). K. Krogh and J.B. Jørgensen excavated Thjod-
hild’s Church during the 1960s (Krogh, 1967; Lynnerup, 1998).
Comparative data were collected from Icelandic, Norwegian, and
Danish samples. The Icelandic sample, excavated in 1905 by V. Steffan-
son, dates around the 14th and 15th centuries and is comprised of
remains excavated from Alftanes Island and Haffiordery (Hooton,
1918). C. Long excavated the Norwegian sample in the 1970s from the
medieval church of St. Gregory’s in Trondheim, Norway (Hanson,
FIGURE 1 Six grade scale used to score mandibular torus
expression in the Norse; grade 1 not shown as it is only evident
through palpation
2
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SCOTT ET AL.
1986). This sample dates from the early 12th century to 1531. While
the Norwegian and Icelandic samples are medieval in age, the Danish
sample came from a variety of Viking age burials dating between A.D.
800 and 1000.
Although the dates of each burial location in Greenland are not
precise, they can be placed in a broad temporal framework. Thjodhild’s
Church, dating to the early years of occupation (ca. A.D. 1000–1150),
is referred to as the Early Eastern Settlement. Burials from the sites of
Sandnes and Anavik make up the Western Settlement sample. Due to
temporal complications and small sample sizes, Gardar, Herjolfnes, and
the Benedictine Convent were combined to create a Middle Late East-
ern Settlement sample that is roughly contemporaneous with the
Western settlement sample (ca. 13th-14th centuries). Radiocarbon
dates on human bone corroborate these temporal assignments (Arne-
borg et al., 1999).
The above data were collected by the first author (GRS). However,
to put the North Atlantic Norse into a broader world context, data
were obtained from a wide variety of published sources. When geo-
graphic areas were underrepresented, we went through the original
data sheets of Christy G. Turner II (CGT II) to fill in the blanks. This was
particularly true for Southeast Asia, Australia and the Pacific, Mesoa-
merica, and South America. We report mandibular torus frequencies
for 335 world populations. From the literature, data were obtained for
42,418 individuals from 202 samples; an additional 7,552 individuals
TABLE 1 Expression of mandibular torus in Vikings, Norwegians, Icelanders, and Norse Greenlanders
Age Grade of Expression Total X
2
X
2
Mean trait
Sample Sex Range n0 1 2 3 4 5 Frequency age sex score
Vikings M 18–30 16 93.8 6.3 0.0 0.0 0.0 0.0 6.3
F 7 100.0 0.0 0.0 0.0 0.0 0.0 0.0 NA
M30622 95.5 4.5 0.0 0.0 0.0 0.0 4.5 NA
F 19 78.9 15.8 5.3 0.0 0.0 0.0 21.1 NA
Total 64 90.6 7.8 1.6 0.0 0.0 0.0 9.4 0.109
Norwegians M 18–30 15 73.3 13.3 13.3 0.0 0.0 0.0 26.7
F 16 43.8 31.3 25.0 0.0 0.0 0.0 56.2 0.036
M30635 54.3 34.3 8.6 2.9 0.0 0.0 45.7 1.447
F 32 43.8 37.5 6.3 12.5 0.0 0.0 56.2 0.333
Total 98 52.0 31.6 11.2 5.0 0.0 0.0 47.8 0.694
Iceland M 18–30 9 44.4 22.2 0.0 11.1 22.2 0.0 55.6
F 15 33.3 40.0 13.3 13.3 0.0 0.0 66.7 1.600
M30615 26.7 13.3 26.7 6.7 26.7 0.0 73.3 2.105
F 43 25.6 39.5 20.9 14.0 0.0 0.0 74.4 0.333
Total 82 29.3 32.9 18.3 12.2 7.3 0.0 70.7 1.353
Greenland Eastern
Early (EE)
M18–30 2 0.0 50.0 50.0 0.0 0.0 0.0 100.0
F 5 0.0 40.0 40.0 20.0 0.0 0.0 100.0 NA
M30620 5.0 40.0 25.0 15.0 15.0 0.0 95.0 1.210
F 7 0.0 14.3 0.0 28.6 28.6 28.6 100.0 NA
Total 34 2.9 35.3 23.5 17.6 14.7 5.9 97.0 2.235
Greenland Eastern
Middle Late (EML)
M18–30 1 0.0 0.0 100.0 0.0 0.0 0.0 100.0
F 10 40.0 40.0 10.0 10.0 0.0 0.0 60.0 NA
M30610 0.0 20.0 40.0 30.0 10.0 0.0 100.0 7.410*
F 17 17.6 41.2 29.4 0.0 11.8 0.0 82.4 1.266
Total 38 18.4 34.2 28.9 10.5 7.9 0.0 81.5 1.553
Greenland Western
Settlement (West)
M18–30 2 0.0 100.0 0.0 0.0 0.0 0.0 100.0
F 10 30.0 50.0 10.0 0.0 10.0 0.0 70.0 NA
M3066 33.3 0.0 16.7 33.3 0.0 16.7 66.7 1.009
F 19 42.1 21.1 15.8 10.5 10.5 0.0 57.9 0.862
Total 37 35.1 29.7 13.5 10.8 8.1 2.7 64.8 1.351
EE: Thjodhild’s Church.
EML: Gardar, Herjolfnes, Benedictine Convent.
West: Sandnes, Anavik.
SCOTT ET AL.
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3
were tabulated from the CGT II database from 133 samples. The total
number tabulated equals 49,970, with the North Atlantic samples
bringing the total to over 50,000. Although there might be minor differ-
ences in how researchers score the lowest grades of mandibular torus,
the large number of samples and individuals smooth out issues associ-
ated with interobserver error.
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METHODS
Mandibular torus is a bony growth expressed on the internal aspect of
the mandible below the lower canine and extending back as far as the
second molar. Trait expression varies among individuals who exhibit
one continuous growth or have expression broken down into two or
more distinct lobes. Determining the degree of torus expression does
not lend itself to interval scale measurement as there are no consistent
landmarks. However, the bony ridges and lumpy nodules that make up
the torus vary considerably in size, both in terms of linear length along
and projection away from the body of the mandible (Hassett, 2006). To
accommodate this variation, a ranked scale was developed that
includes grade 0 (absence) and grades 1 through 5 (increasingly pro-
nounced degrees of expression). When a mandible lacks a torus alto-
gether, this is determined through a combination of visual examination
and palpation. When there are no visible signs of torus and no slight
bony projection detectable by touch, the individual is scored as grade
0. A rank of 1 is assigned to a torus that cannot be visibly identified
but is evident by palpation. Grades 2 and above are all visually observ-
able and range from slight to pronounced protuberances (Figure 1).
4
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RESULTS
4.1
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Torus expression by age and sex
Table 1 shows the class frequency distributions for mandibular torus in
the six Scandinavian samples broken down by two adult age categories
and sex. Although age may be implicated in torus development, there
is no significant difference between young adults and older adults in
any sample. Torus was so rare in Vikings that a test of sex difference
was not possible. For the remaining samples, four of five show no sig-
nificant difference between males and females. There was a significant
difference for the Eastern Middle Late sample but small sample sizes
may be implicated in this finding. At least for the samples in this study,
age and sex differences are minimal or nonexistent.
4.2
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Geographic variation
While the Scandinavian samples exhibit no patterned differences in
age and sex, they show pronounced temporal and geographic variation.
In the Viking age sample, mandibular torus is extremely rare. A few
jaws exhibit palpable tori but only one shows a small grade 2 form.
Over 90% of this sample fails to show any torus whatsoever and mean
trait expression is 0.109. The closest sample to the Vikings is medieval
Norwegians. For this group, about half (47.8%) of the sample exhibits
some form of torus with palpable expressions the most common
(31.6%). Mean trait expression is 0.694. The Icelanders and Green-
landers differ dramatically from the Vikings and Norwegians. The most
pronounced tori are found in the Eastern Early sample, which has a
total frequency of 97% and a mean trait score of 2.235. These values
are significantly higher than those for Icelanders (70.7%; mts 51.353)
FIGURE 2 Class frequency distributions for mandibular torus in
the Greenlandic Norse, along with Vikings and medieval Norwegians
and Icelanders
4
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SCOTT ET AL.
and the two medieval Greenlandic samples (81.5 and 64.8%;
mts 51.553 and 1.351). This dramatic difference is illustrated in Figure
2 that shows the distribution of torus expression in the two European
samples and the four North Atlantic samples.
5
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DISCUSSION
The Greenlandic Norse were exposed to an inhospitable climate
where wood was scarce and agriculture impossible due to short
growing seasons and the presence of permafrost. During the 500
year Norse occupation of Greenland, expression of mandibular torus
was at a maximum in the settlement period population (see Table 1
and Figure 2). It is difficult to determine the extent to which environ-
mental factors in Greenland contributed to this pattern because the
settlement period population came directly from Iceland. Although
we examined medieval Icelanders, we do not know how settlement
period populations from Iceland exhibited mandibular torus. Medie-
val Greenlanders show dramatic torus frequencies and expressions
consistent with observations of medieval Icelanders, but these are
less pronounced than what we see in the earliest colonizers of
Greenland. All three Greenlandic samples and the Icelanders exhibit
more mandibular torus than related populations from Denmark and
Norway. Given the presumably similar genetic backgrounds of Scan-
dinavian populations in Europe and the Norse colonists in the North
Atlantic, it seems that environmental pressures trump genetic back-
ground in determining mandibular torus expression in these
TABLE 2 Mean frequencies of mandibular torus for 15 regional groups
Regional group kMean % S.D. 95% confidence limits References
Greenland and Iceland 11 0.512 0.2036 0.375–0.649 (Axelsson & Hedegård, 1981; Drenann, 1937; Fischer-Møller,
1942; Igarashi, Ohzeki, Uesu, Nakabayashi, & Kanazawa, 2008;
Oschinsky, 1964; Steffensen, 1969)
Northern Europe 15 0.177 0.1418 0.098–0.255 (Alvesalo & Kari, 1972; Axelsson & Hedegård, 1981; Drenann,
1937, Furst & Hansen, 1915; Haugen, 1992; Howells, 1941; Kolas
et al., 1953; McLoughlin, 1950; Mellquist & Sandberg, 1939;
Oschinsky, 1964; Schreiner, 1935; Sognnaes, 1954) (CGT 6)
Southern Europe 10 0.147 0.1633 0.030–0.264 (Cunha, 1994; Czarnetzki, 1975; Galera, Garralda, Casas, Cleuve-
not, & Rocha, 1995; Hrdlička, 1940; Reichart, Neuhaus, &
Sookasem, 1988; Rouas & Midy, 1997; Witkop & Barros, 1963)
North Africa and
Middle East
17 0.030 0.0635 0.003–0.062 (Irish, 1993; Khaki, 2000; Salem, Holm, Fattah, Basset, & Nasser,
1987; Sawair, Shayyab, Al-Rabab’ah, & Saku, 2009) (CGT 1)
South Asia 8 0.163 0.1277 0.056–0.270 (Kaul & Anand, 1979; Ohno, Sakai, & Mizutani, 1988; Shah,
Sanghavi, Chawda, & Shah, 1992; Zoubov, 1973) (CGT 1)
Sub-Saharan Africa 27 0.039 0.0692 0.012–0.067 (Adeyemo, Emeka, Taiwo, & Adeyemi, 2009; Agbaje, Arowojolu,Kolude,
& Lawoyin, 2005; Bruce, Ndanu, & Addo, 2004; de Villiers, 1968; Dosum,
Arotiba, & Ogunyinka, 1998; Drenann, 1937; Ihunwo & Phukubye, 2006;
Irish & Konigsberg, 2007; Rightmire, 1972; Shaw, 1931) (CGT 2)
North Asia 56 0.408 0.1894 0.357–0.458 (Akabori, 1939; Dodo, 1974; Dodo & Ishida, 1987; Djurić-Srejić&
Nikolić, 1995; Hrdlička, 1940; Igarashi, in press; Igarashi et al., 2008;
Miyashita, 1935; Ohno, Sakai, & Mizutani, 1988; Pechenkina &
Benfer, 2002; Rouas & Midy, 1997; Sakai, 1954; Sugihara et al.,
2003; Tamaki, Marzola, & Tamaki, 1970; Zoubov, 1973) (CGT 29)
Southeast Asia 31 0.097 0.0989 0.061–0.134 (Hashim, Haidar, & Kalsom, 1983; Jainkittivong, Apinhasmit, &
Swasdison, 2007; Kerdpon & Sirirungrojying, 1999; Nair, Samar-
anayake, Philipsen, & Itthagarun, 1996; Reichart et al. 1988; Van
den Broek, 1941; Zoubov, 1973) (CGT 24)
Australia-Melanesia 31 0.018 0.0344 0.006–0.031 (Campbell & 1925; Fenner, 1939; Hrdlička, 1940) (CGT 27)
Polynesia and
Micronesia
15 0.030 0.0492 0.002–0.057 (Turner & Scott, 1977; Witkop & Barros, 1963) (CGT 12)
Circumpolar
(Eskimo-Aleuts)
38 0.596 0.1825 0.536–0.656 (Dodo & Ishida, 1987; Furst & Hansen, 1915; Hrdlička, 1940; Jarvis
& Gorlin, 1972; Jorgensen, 1953; Mayhall, 1970; Mayhall, Dahlberg,
& Owen, 1970; Mayhall & Mayhall, 1971; Moorrees, 1957;
Moorrees et al., 1952; Oschinsky, 1964; Ossenberg, 1978; Russell &
Huxley, 1899; Schreiner, 1935; Scott, 1991; Steffensen, 1969; 85)
Native North America
(North)
14 0.290 0.2000 0.174–0.405 (Cybulski, 1975; Ossenberg, 1978) (CGT 3)
Native North America
(South)
31 0.233 0.1882 0.164–0.302 (Birkby, 1973; Blakely, 1973; Buikstra, 1972; El-Najja, 1974;
Hooton, 1918; Hooton, 1930; Hrdlička, 1940; Ossenberg, 1978;
Sublett, 1970; Wiltschke-Schrotta, 1988) (CGT 9)
Mesoamerica 13 0.053 0.0854 0.001–0.104 (Escobar, Conneally, & Lopez, 1977) (CGT 10)
South America 18 0.053 0.0592 0.024–0.083 (Balaez, Diaz, & Perez, 1983; Bernaba, 1977; Hrdlička, 1940;
Sawyer et al., 1979; Yaacob, Tirmzi, & Ismail, 1983; 85) (CGT 9)
World total 335 0.224 0.2425 Literature (202); CGT (133)
SCOTT ET AL.
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5
colonizing populations. To evaluate this question further, these six
Scandinavian samples are viewed in the context of torus expression
around the world.
5.1
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World variation
The 335 samples tabulated for total mandibular torus frequencies were
broken down into 15 major geographic areas (see Table 2). The first
group, representing the Norse colonists of Greenland and Iceland, does
not include the samples reported in this study. Those were independ-
ent observations provided by other researchers. Western Eurasia is
broken down into four regions, including Northern and Southern
Europe, North Africa-Middle East, and South Asia. Africa has been less
intensively studied for torus than other regions so there is only a single
Sub-Saharan Africa category. Asia and the Pacific are more complex.
Asia is divided into North Asia and Southeast Asia. The Pacificisbro-
ken down into Australia-Melanesia and Polynesia-Micronesia. Over a
third of the world samples come from the Americas which are divided
into five regions: Circumpolar, North America (North), North America
(South), Mesoamerica, and South America.
In terms of percentages, the geographic pattern of mandibular
torus variation is clear if regions are broken down into high (40%1),
moderate (20–39%), low (10–19%), and very low frequency (<10%)
groupings. Not surprisingly the high frequency group is headed by Cir-
cumpolar populations (Eskimo-Aleuts) with a mean frequency of
59.6%. Greenland and Iceland have the next highest average frequency
(51.2%), followed by North Asians (40.8%). The high frequencies in Cir-
cumpolar and North Asian populations likely reflect genetic relation-
ships to some extent. The same cannot be said for Greenland and
Iceland where convergence rather than similar genetic backgrounds is
indicated. Only two regions fall in the moderate frequency category:
American Indians in the northern reaches of North America and those
found at lower latitudes as far south as the U.S.-Mexican border. Popu-
lations in the northern and southern parts of Europe, along with Asiatic
Indians, fall in the low frequency grouping. Almost half of all world
samples fall in the very low frequency group. Southeast Asia is close to
10% (i.e., 9.7%) but the remaining six groups are at or below 5%. Fre-
quencies are very low in Sub-Saharan Africans along with North
Africans-Middle Easterners. The world’slowestfrequenciesareinthe
Pacific, especially Australia and Melanesia, although Polynesia and
Micronesia are not far behind. In marked contrast to their neighbors to
the north, American Indians in Mesoamerica and South America have
low mean torus frequencies that are exactly the same at 5.3%.
In addition to the broad regional characterizations, individual
sample frequencies were plotted on a world map to illustrate the
pattern of variation for mandibular torus. Figure 3 shows that man-
dibular torus is strongly correlated with latitude. High latitude popu-
lations of both Asian and European descent show the highest torus
frequencies in the world. Torus frequencies are markedly reduced in
populations approaching the equator. The clinal maps are basically
blank in Africa, Australia, the Pacific, Mesoamerica, and South Amer-
ica despite being represented by dozens of samples and thousands
of individuals. The contrast in the Americas is especially telling.
North American Indians differ to some extent from Mesoamerican
and South American Indians, but the distinction between these areas
for mandibular torus is far more dramatic than we see in genetic or
dental markers (cf., Cavalli-Sforza, Menozzi, & Piazza, 1994; Scott &
Turner, 1997).
The suggestion that mandibular torus development might be asso-
ciated with wear is without foundation for a very basic reason. North-
ern populations have no monopoly on tooth crown wear. Researchers
who have not worked with Eskimo-Aleut samples often assume they
show an extraordinarily high degree of wear, but this is not the case.
They show pronounced wear but no more than countless other groups
who live at or near the equator and rarely express mandibular torus (e.
g., Australian aboriginals). If bruxism impacts mandibular torus, occlusal
stress may play a small role in its development but only a small role.
What is it about northern latitudes that trigger unusually large tori?
Beyond stress, cold and a high protein diet are two major factors that
might be involved in torus formation. Until a test is devised to tease
out divergent proximate causes, we can only conclude that genetics
plays a small role but environmental agencies play the predominant
FIGURE 3 World map showing clinal variation in mandibular torus frequencies; the highest frequencies are shown as dark gold with the
lowest frequencies as light gold
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SCOTT ET AL.
role in the manifestation of frequent and pronounced mandibular tori
in northern populations from disparate genetic backgrounds.
ACKNOWLEDGMENTS
Remarkably, the late Christy G. Turner II collected more data on
mandibular torus than any other single individual but, to the authors
knowledge, he never did anything with these data. He published
extensively, but his efforts were devoted primarily to how tooth
crown and root morphology could be used to address anthropologi-
cal issues (e.g., peopling of New World and Pacific). Going through
his original data sheets allowed us to evaluate populations from geo-
graphic regions largely unknown for mandibular torus frequencies (e.
g., Australia, New Guinea, Mesoamerica). Although the picture that
emerged from a consideration of 202 sample frequencies taken from
the literature pointed strongly in the direction of latitudinal clines in
torus frequencies, the addition of 133 samples from the CGT collec-
tion solidified the point considerably, especially for equatorial
populations.
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