Comparative craniofacial variation in Navajo Indians and North American Caucasians.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 76:145-154 (1988) Comparative Craniofacial Variation in Navajo Indians and North American Caucasians GERALD S. PHIPPS, REBECCA Z. GERMAN, AND RICHARD J. SMITH Department of Orthodontics (G.S.P,R.Z.G.,R .J.S.) and Department of Biomedical Science (R.Z.G.), Washington University School of Dental Medicine, St. Louis, Missouri 63110 KEY WORDS Cephalometrics, Variability, Craniofacial morphology ABSTRACT Landmarks digitized from lateral cephalometric radiographs of 107 Navajo Indians between 10 and 12 years of age were analyzed to determine coefficients of variation or standard deviations for 38 cephalometric measurements. These values were compared with the same measures of variation for identical measurements on North American whites derived from the Michigan and Philadelphia Growth Studies. For the majority of variables, there were no differences between groups.Variation for the genetically and environmentally isolated Navajo Indians was the same as that of the highly diverse Caucasian samples. However, measurements of upper, lower, and total anterior facial height (N-ANS,ANS-Me, and N-Me, respectively) indicate that these features are substantially less variable in Navajo Indians relative to the Michigan and Philadelphia populations. Phenotypic variation of anthropometric traits within and among isolated human populations has been the subject of considerable investigation. The results of several studies suggest that there is a slight reduction in variability within isolated groups when compared with industrialized, cosmopolitan populations (Hunt, 1966; Neel et al., 1964; Schull and Neel, 1965; Smith and Bailit, 1977b; Stern, 1973). Others, however, have reported higher variation within isolated populations. The Hutterites, a highly isolated and inbred religious sect distributed in Anabaptist colonies in the western United States and Canada, were examined by Howells (1966). He concluded that this group did not exhibit reduced variability in anthropometric traits. On the contrary, intrafamily variation was found to be greater than interfamily variation, demonstrating the maintenance of variability in the smallest of population units. Recent studies (Harper, 1980; Szathmary, 1983, 1984) examining variation in gene frequencies for Native Americans have demonstrated a consistent high degree of variation within, rather than between, groups. Investigators finding reduced variation in isolated populations generally invoke de- 0 1988 ALAN R.LISS, INC. creased genetic variation due to homozygosity and decreased environmental variation as the mechanisms for the variance reduction. Those studies reporting increased or equivalent variation in isolated populations generally explain these findings on the basis of decreased heterotic buffering. That is, within any population, increasing homozygosity may reduce the developmental homeostasis seen in heterozygotes, resulting in greater phenotypic variance (Lerner, 1954). For craniofacial anthropometric traits, comparison of variability in urban and isolated populations is complicated by an additional consideration. Westernization seems to be accompanied by an increase in the prevalence of malocclusion (Bjork and Helm, 1969; Corruccini et al., 1983; Hunt, 1961; Lombardi and Bailit, 1972). A dietary basis for this observation, related either to decreased dental attrition (Begg, 1954; Lombardi, 1982) or to decreased functional stimulation of jaw growth (Corruccini, 19841, is more likely than a genetic admixture effect (Chung et al., 1971; Smith and Bailit, 1977a). In either case, an increase in the Received September 21, 1987; accepted January 18, 1988 146 G.S. PHIPPS ET AL. variability of facial skeletal dimensions is likely to accompany this increase in malocclusion (Mann, 1979). Although skull metrics have been exhaustively studied, both radiographically in living subjects and directly on skeletal specimens, relatively few workers have directly considered the question of comparative variability. In this study, we compare a population of Navajo native Americans to two urban populations specifically to examine changes in variability among populations, age groups, and between sexes. MATERIALS AND METHODS Sample selection The Navajo Indians are related to the Athapascan-speaking groups currently located on the Northwest Pacific Coast of Canada and the United States. About 1,000 years ago, the Navajo migrated to the southwest United States (Troup et al., 1982). Currently, 200,000 Navajo occupy a 30,000square-milereservation in northeast Arizona, northwest New Mexico, and small portions of Utah and Colorado (Bureau of Census, 1984). The Navajo population is well-suited for genetic studies due to a restricted gene pool, resulting from consanguinity; founders effect; and limited genetic admixture (Cole, 1964; Troup et al., 1982). The degree of isolation this tribe has maintained has limited genetic mixture with other population groups and has aided in keeping the Navajo racial strain relatively pure. By examining gene frequencies, Williams et al. (1985) demonstrated an average Caucasoid admixture for Southern Athapascan groups, including Navajo, of about 4%. As described by Spuhler and Kluckhohn (19531, “the Navajo do not concentrate their population into villages. Rather, the community is composed of biological families (or more usually such families combined into extended families with matrilineal descent and matrilocal residence) widely spaced in small houses or hogans.” The higher level of consanguinity seen in the Navajo, relative to the general population, is most likely a result of geographic and cultural isolation and not due to incest (Kluckhohn and Leighton, 1947; Downs, 1972). Population sample Pretreatment lateral cephalometric radiographs and study models of 107 Navajo In- dians (Table 1)were obtained from the Navajo Orthodontic Program at Shiprock, New Mexico. The following criteria were used in the selection of subjects for this study: 1. Navajo Indians of 4 4 bloodline (no known admixture) as determined from birth certificates and other documentation presented to the Public Health Service. 2. Residence of record and place of birth located on the Navajo Reservation. 3. Age 10 to 12 years, as determined from documentation accompanying the cephalometric radiographs and study models. 4. No history of previous orthodontic treatment. 5. No significant medical history. Although every attempt was made to eliminate bias in sample selection, it should be understood that the records examined in this study may not be entirely representative of the Navajo population. Rather, they represent the records of subjects with a malocclusion significant enough to have justified the taking of orthodontic records. However, for any result showing decreased variability in Navajos, this sample selection is conservative. Since all subjects exhibited some treatable degree of malocclusion, we would expect variability in this sample to be higher than in a totally random Navajo sample that included individuals with ideal occlusion. Even when groups of subjects with one specific type of malocclusion have been compared to normal occlusion groups, the malocclusion group has been found t o have a generalized increased variation in craniofacial morphology (Cangialosi, 1984; Isaacson et al., 1971; Mann, 1979). Data collection and measurement reliability Cephalometric radiographs were taken with a Siemens Orthopantamograph a t a distance of 60 in and subject-film distance of 15 cm. All radiographs were evaluated identically. Landmark coordinates were recorded using a Numonics 2400 Digitizer, IBMAT computer, and the Washington University ORTHODIG program (Dunford-Shore and German, 1986), and then converted directly into angular and linear measurements related to the Bjork (1947), Downs (1948), and Steiner (1960) analyses. Repeated measurements on a series of ten radiographs resulted in no significant error (P < .005) in measurement technique. The average error in measurement technique was 147 CRANIOFACIAL VARIABILITY IN NAVAJO INDIANS TABLE 1. Sampb sizes by age and sex Age (yr) Navajo Michigan Philadelphia 10 Male 11 12 10 Female 11 12 10 46 45 10 43 54 12 44 59 34 35 61 24 30 50 17 27 69 0.25 mm with the largest average error being 0.63 mm for location of the apex of the maxillary central incisor. Choice of variables and statistics Measurements provided by the three cephalometric analyses generated 85 variables for comparison with other groups. The Michigan Growth Study (Riolo et al., 1974) and Philadelphia Growth Study (Saksena et al., 1987) were chosen for comparison because they are based on large, random samples and they report both means and standard deviations of measurements by age and sex. Of the original 85 variables, 32 coincided with the Michigan Growth Study and 19 coincided with the Philadelphia Growth Study (Table 2). The data for each of these variables was statistically analyzed using the SYSTAT package (Wilkinson, 1986) on an IBM-AT computer. The definitions of all cephalometric landmarks used in Table 2 are given in Riolo et al. (1974) and Saksena et al. (1987) and are illustrated in Figure 1. A variety of statistical methods have been used to compare variability within and among groups. Comparison of standard deviations has proven useful in some previous studies (Howells, 1966; Hunt, 1966). However, the standard deviation is of limited value in comparisons of variability for large dimensions since it has a positive correlation with the mean (Haugen, 1977, 1978a,b, 1979, 1980). Nee1 et al. (1964) utilized the coeEcient of variation (the standard deviation divided by the mean) to compare Xavante Indians with residents of Hamburg, Germany. The coefficient of variation is best employed when the magnitude of the means are large enough to require a relative expression of variability in percent of the mean (Sokal and Braumann, 1980). The evaluation of coefficients of variation can be both descriptive (Yablokov, 1974) and inferential (Galler and Gould, 1979). In this study, we will first qualitatively assess differences in variation between samples for each variable. Then, using a complete linear model with three Fig. 1. Landmarks used to derive the angular and linear measurements listed in Table 1. Symbols for identified points are as follows: nasion (N), sella (S), porion (Po), articulare (Ar), orbitale (Or), anterior nasal spine (ANSI, posterior nasal spine (PNS), subspinale (A), incision superius (Is),incision inferius (Ii), infradentale(Id),occlusal plane (OP), supramentale (BD), pogonion (Pg), menton (Me), and gonion (Go). factors-age, sex, and sample-we will test the hypothesis that the coefficient of variation (or the amount of variation) was equal in each treatment. For some measurements, the standard deviation is a more appropriate measure of variability than the coefficient of variation. These variables include angular and linear measurements that have positive and negative values. The resulting mean values fluctuating around zero markedly inflate coefficients of variation. RESULTS The comparative statistics for the selected variables are listed in Table 2. The six columns in each table for each population represent measurements of Variability for the AT-S Go-pg Angular skeletal measurements SNA SNB S-N-ANS SN-Pg G0-h Linear skeletal measurements (mm) Ar-N N-S &-Id Ar-B Ar-PNS ANS-PNS Ar-Ii N-ANS ANS-Is N-Me ANS-Me Variable 4.2 6.5 4.1 3.7 7.5 7.1 4.6 5.8 10.0 3.9 6.5 7.5 6.9 3.4 3.9 2.7 5.0 3.3 4.7 4.1 3.9 4.3 6.9 3.9 4.1 3.3 9.6 4.2 6.2 9.5 12.1 4.7 4.2 4.4 4.8 4.3 10 M 11 3.9 4.1 3.5 3.5 9.4 7.5 4.0 4.9 7.3 3.4 4.8 6.8 8.3 4.0 4.7 4.1 4.7 3.8 3.8 4.6 2.6 5.1 10 4.4 3.9 3.1 3.8 8.0 5.4 2.1 6.1 7.7 3.9 5.4 10.6 8.9 3.0 12 Navajo 3.8 3.3 3.8 3.1 5.2 6.2 4.9 5.9 4.6 3.6 4.7 3.4 - I - 3.9 4.2 3.4 3.2 6.7 4.8 3.8 5.9 7.4 4.8 7.1 10 4.3 5.5 5.9 5.8 10.3 6.5 6.1 4.2 8.1 3.9 6.4 8.9 11.8 6.0 12 4.4 4.6 3.8 3.8 9.4 6.5 5.3 3.4 8.4 3.8 5.5 8.0 6.6 7.0 F 11 3.7 3.4 3.7 5.0 3.8 3.7 4.0 3.8 6.7 4.3 4.6 6.3 6.5 4.9 6.8 - 11 M 4.1 3.5 4.3 4.5 3.7 4.2 4.2 3.9 6.4 5.5 4.9 6.6 7.1 5.1 7.2 - 12 4.7 5.0 5.1 5.8 4.6 4.6 4.4 4.5 - - - 4.9 4.0 4.4 4.7 6.6 7.4 4.7 6.3 10.1 5.5 7.0 - 11 F 4.7 3.8 5.1 5.0 7.6 5.8 5.7 7.1 10.3 5.8 7.5 10 Michigan 4.4 4.4 4.3 5.0 4.4 4.0 4.6 4.4 6.9 5.9 5.0 6.9 9.7 5.1 5.7 - 12 4.0 4.0 4.2 3.9 4.4 7.1 6.8 9.9 5.2 - 7.1 5.5 - 4.0 3.9 10 4.0 4.4 3.8 4.3 6.3 5.9 4.2 6.3 6.7 9.9 5.5 - 4.3 4.4 - 11 M TABLE 2. Variability (coefficientsof uariatian or standard deuiatwns) for all measurements separately by age, sex, and population 4.0 4.2 4.4 4.1 4.2 6.6 6.9 9.0 4.6 - 7.1 - 4.2 4.1 - 12 4.1 3.9 4.4 4.3 4.8 6.0 8.4 9.8 4.6 - 6.3 5.8 - 4.7 3.2 10 Philadelphia F 4.6 4.8 4.9 5.2 5.9 7.2 8.2 9.3 6.3 7.1 6.9 - - I 4.8 4.3 11 4.1 4.1 4.3 4.3 4.9 6.9 7.7 7.4 5.7 - 4.4 3.8 6.7 - 12 Go-MdSN ANS-PNsIGo-Me ArWGo-Me N-S-Ar SAr-Go Po-Or/N-Pg Angular skeletal measurements (standard deviations) ANB N-A-Pg OP/SN Po-Or/Go-Me Po-OdOP A-B/N-Pg Dental measyements At01 1 to &Me Dental measurements btandard deviations) 1toOP IS to A-Pg (m) ISto N-A (m) 1to N-A - to N-B (mm) 1to N-B 17.0 17.0 1.7 2.9 4.9 5.8 2.7 6.4 3.8 6.6 5.9 4.0 9.2 5.8 7.5 3.5 2.4 6.6 1.9 7.3 15.3 26.9 4.3 5.6 4.3 3.0 3.1 7.1 2.9 4.3 3.1 3.8 8.7 8.4 7.8 4.1 2.8 5.8 1.7 8.2 10.6 17.8 3.0 4.4 4.4 5.2 2.7 6.1 2.9 6.3 4.9 3.7 4.7 4.4 4.3 3.1 2.9 8.4 1.2 5.5 6.3 2.3 1.9 5.3 1.4 5.5 6.5 6.5 2.8 5.8 2.9 3.6 2.8 4.2 9.8 11.9 3.2 3.7 3.6 3.5 6.7 3.1 2.7 5.6 1.4 6.2 8.9 6.0 2.3 5.3 3.3 5.5 4.7 3.0 11.8 15.4 6.1 3.0 3.9 5.3 4.6 2.0 3.5 8.1 1.4 5.6 7.1 7.0 2.9 6.2 4.2 6.5 5.0 4.3 14.1 14.1 3.9 5.8 5.0 6.1 5.5 2.6 2.2 5.3 2.3 5.6 6.9 5.3 2.0 4.9 3.2 5.0 3.7 2.7 4.1 - 13.5 16.5 5.6 2.5 2.3 6.0 2.5 6.0 7.3 5.6 1.9 4.5 3.8 4.7 3.6 2.6 4.2 - 13.5 16.3 - 6.4 2.6 2.7 5.7 2.6 6.4 7.6 6.2 2.1 4.8 3.7 5.5 4.8 2.7 14.5 17.9 4.6 6.9 2.4 2.2 7.0 2.1 6.2 7.1 7.2 6.4 2.7 2.4 6.1 2.3 6.0 7.1 6.4 2.2 4.5 3.6 4.4 2.9 3.2 3.2 4.2 2.7 5.7 3.5 4.2 3.7 3.7 - - 16.1 18.9 - _ 10.6 17.6 6.9 3.0 2.8 6.5 2.5 6.7 8.0 6.9 2.4 5.5 3.3 5.2 3.0 3.6 15.5 19.8 3.5 150 G.S. PHIPPS ET AL. TABLE 3. Analysis of variance of complete model SOUm Age Sex Sample Age sex * Mean-square F-ratio P 7.902 10.743 13.244 2 1 2 3.951 10.743 6.622 0.320 0.870 0.536 0.726 0.352 0.586 3.677 2 1.838 0.149 0.862 Sum-of-squares DF Age * Sample sex * Sample 6.368 4 1.592 0.129 0.972 11.896 2 5.948 0.482 0.618 Age * sex * Sample Error 19.867 4,150.431 4 336 4.967 12.352 0.402 0.807 Tests for interaction effects between variables are indicated by asterisks. two sexes a t the ages 10,11, and 12. In most instances, the value listed is the coefficient of variation. Where standard deviations are reported instead, they are clearly indicated. For the majority of variables, no apparent patterns were evident. For most variables, the group with the lowest or highest coefficient of variation was not consistent with respect to age, sex, or sample. In most cases, the range of the coefficients of variation within a variable was not remarkable. For a few variables, specific patterns emerged. Ar-PNS (articulare to posterior nasal spine), which is sometimes used as an approximate measure of the upper pharyngeal space, was more variable a t all ages and in both sexes for the Navajo group when compared to the Michigan group. The coefficient of variation of 11-NB (lower incisor to the nasion-B point line), a sagittal measure of the position of the mandibular central incisor in relation to the anterior limits of the facial skeleton, was always lower in Navajos than in the Michigan sample, for both sexes at all ages. The coefficients of variation for upper, lower, and total anterior facial heights (N-ANS, ANS-Me, and N-Me, respectively) are suggestive of substantially reduced variation in Navajo Indians, relative to both the Michigan and Philadelphia samples. Of the 36 possible pairwise comparisons for these variables, there were only two exceptions to this pattern. Eleven-year-old males from Philadelphia and twelve-year-old females from Michigan had a lower coefficient of variation than their age- and sex matched Navajo counterparts for one measurement each. Table 3 contains the results of a complete unbalanced analysis of variance of all factors and interactions. Only measurements from Table 2 expressed as coeftkients of variation were included in this analysis, producing an N of 354. The squared multiple R for the complete model was 0.018. No main factor or interaction even remotely approached significance. We thus accept the null hypothesis of equal coefficients of variation among treatments. Across all variables there is no difference in variation among samples, age groups, and sexes. DISCUSSION There have been numerous studies of craniometric traits, generally related to one of two broad categories. Many studies have reported and compared sample means derived from cephalometric radiographs of living subjects (Altemus, 1968; Broadbent et al., 1975; Brown and Barrett, 1964; Craven, 1958; Gresham, 1968; Packard, 1967; Richardson, 1980). The other common category of study design has looked at metric traits in the skulls of non-living subjects (Abdushelishvili, 1984; Brown, 1973; Cederquist and Dahlberg, 1979; Haugen, l977,1978a,b, 1979,1980; Kanda, 1964; Kanda et al., 1968; Key and Jantz, 1981; Tattersall, 1968).These studies provide extensive data on differences in craniofacial form, but not on differences in form variation. Previous studies comparing phenotypic variation of anthropometric traits in isolated populations to industrialized groups suggest that there is only a slight reduction in variability within the isolated group (Hunt, 1966;Neel et al., 1964; Schull and Neel, 1965; Smith and Bailit, 1977b). Neel et al. (1964) evaluated the variability of an assortment of traits in Xavante Indians, described as a “small, quite endogamous group with a relatively high coefficient of inbreeding where CRANIOFACIAL VARIABILITY IN NAVAJO INDIANS polygamy is common and sterility is rare.” The intragroup variation for the Xavante was only slightly less than that of the cosmopolitan population of Hamburg, Germany. Smith and Bailit (1977b), comparing the variation of occlusion and dental arches among an isolated group of Melanesians with that of industrialized groups, demonstrated only a slight reduction in variance between the groups. They concluded: “the maintenance of a large amount of phenotypic variation when there are reasons to expect a decrease in both environmental and genetic variance cannot be satisfactorily explained.” The results of the present study indicate that there are no differences in overall facial variability between young adolescent Navajo Indians and highly diverse Caucasian samples from Philadelphia and Michigan. The discussion of craniofacial trait variability between populations has received limited attention in the literature. When between population comparisons were made, it was generally for the purpose of distinguishing population groups from one another on the basis of dimension and form, rather than observed levels of variation (Altemus, 1960; Howells, 1972; Kowalski et al., 1975). A series of studies by Koski (1973) and associates (Vinkka and Koski, 1975; Vinkka et al., 1975) examined variability in the angular relationship between specific craniofacial traits, represented as anatomic lines traced on lateral cephalograms. Although their method is interesting and informative, it is also unique, and does not allow for comparison to this or most other studies. A comprehensive evaluation of craniofacia1 variability has been presented by Haugen (1977,1978a,b, 1979,1980) on the upper and middle face of medieval skulls from Oslo. Haugen found facial height variables to be in the “medium range of variability.” Using the standard deviation for statistical comparisons, Haugen demonstrated greater variability in males than in females. However, comparisons based on the coefficient of variation showed no sex differences. Reinbold et al. (1985), in an investigation of cranial dimensions in relation to differences in climate, found increased susceptibility of males to short-term environmental variation. However, there was no indication of a significant sex differences in variability within groups for any of the populations examined in the present study. 151 The most interesting exception to the general finding of similar variation within groups is the distinctly reduced variability in measurements of anterior facial height (N-Me), upper anterior facial height (N-ANS), and lower anterior facial height (ANS-Me) for Navajo Indians. As reviewed by Woodside and Linder-Aronson (19791, the correlations between these three measurements within populations are generally low. The consistent results for the three measurements can therefore be considered to strengthen the observation that there is a real difference in the variability of anterior vertical facial height among the groups included in this study. The obvious question to be considered is whether this reflects a biological reduction in variability of anterior facial height of the Navajo or an increase in variability of the Michigan and Philadelphia samples, and whether this difference might be due to genetic and/or environmental influences. This is a classic question which has been the topic of extensive investigation (Harris et al., 1973; Hunter et al., 1970; Kraus et al., 1959; Lundstrom, 1955; Watnick, 1972). The general tendency in the literature has been to attribute greater influence to genetic factors than to environmental ones. Nevertheless, particularly for anterior facial height, environmental factors should not be ruled out. Consistency of diet, respiratory allergies, climate, and head posture, among other variables, have an important effect on craniofacial dimension and form (Beals, 1972; Corruccini et al., 1983; Corruccini, 1984; Hunt, 1961; Nakata et al., 1974; Shapiro, 1969; Shea, 1977; Tarvonen and Koski, 1987; Waugh, 1937). The issue of diet consistency is perhaps the most interesting for the present sample. Hunt (1961) suggested that the decreased facial height seen in skulls of Australian Aborigines and early unacculturated Europeans might be related to a combination of attrition and increased forces of mastication, limiting vertical growth of the upper face. Corruccini et al. (1983) studied the dental casts of 340 Pima Indians between the ages of 11-30 and 31-50 and demonstrated less variability in occlusion for the older Pima, raised on a less refined diet. In a series of studies of laboratory animals given a soft diet, Corruccini and Beecher (1982, 1984) and Beecher et al. (1983) identified both dental and skeletal effects strongly suggestive of a positive association between mastication and jaw development. 152 G.S. PHIPPS ET AL. One of us (G.S.P.) spent 14 months working with and observing this Navajo population prior to the onset of this study. Based on these personal observations, any hypothesis of dietary differences between 10-12-year-old Navajo children and their Michigan and Philadelphia counterparts are considered unlikely. Living conditions on the Navajo Reservation have been substantially modernized over the last decade. Automobiles, paved roads, supermarkets, and fastfood restaurants provide a notable influence in the modern Navajo society and resulting diet. Children presently in a 10-12-year age group do not subsist on a traditional Navajo diet. Thus we rule out the explanation that observed differences in facial variability are due to population differences in diet. It is more likely that anterior facial height is less variable in Navajo Indians due to decreased genetic variation. Several other studies have confirmed that heritability and familial resemblances are greater for anterior vertical facial dimensions than for most other metric features of the skull (Byard et al., 1985; Lundstrom and McWilliams, 1987; Nakata et al., 1974; Szopa, 1976). Broadbent, BH, Sr, Broadbent, BH, Jr, and Golden, WH (1975)Bolton Standards of Dentofacial Developmental Growth. St. Louis: C.V. Mosby Company. Brown, T (1973)Morphology of the Australian Skull. Canberra: Australian Institute of Aboriginal Studies. Brown, T, and Barrett, MJ (1964)A roentgenographic study of facial morphology in a tribe of Central Australian Aborigines. Am. J . Phys. Anthropol. 22:33-42. B m a u of Census (1984)America.n I n d i a n h a s and Alaska Native Villages: 1980.Washington, D.C.: U.S.Department of Commerce. Byard, PJ, Poosha, DVR, Satyanarayana, M, and Rao, DC (1985)Family resemblance for components of craniofacial size and shape. J. Craniofac. Genet. Dev. Biol. 5229-238. Cangialosi, TJ (1984)Skeletal morphologicfeatures of anterior open bite. Am. J . Orthod. 85:28-36. Cederquist, R, and Dahlberg, AA (1979)Age changes in facial morphologyof a n Alaskan Eskimo population. Int. J. Skel. Res. 639-68. Chung, CS, Niswander, JD, Runck, DW, Bilben, SE, and Kau, MCW (1971)Genetic and epidemiologicstudies of oral characteristics in Hawaii‘s schoolchildren. 11. Malocclusion. Am. J. Hum. Genet. 23:471-495. Cole, FtL (1964)A Cephalometric Evaluation ofthe Navajo Indian. M.S. Thesis, h m a Linda University. Corruccini, Rs (1984)An epidemiological transition in dental occlusion in world populations. Am. J. Orthod. 86:419-426. Corruccini, RS, and Beecher, RM (1982)Occlusal variation related to soft diet in a nonhuman primate. Science 218:74-76. Corruccini, RS, and Beecher, EW (1984) Occlusofacial morphological integration lowered in baboons raised on ACKNOWLEDGMENTS a soft diet. J. Craniofac. Genet. Dev. Biol. 4:135-142. The authors wish to thank Dr. C. Michael Corruccini, RS, Potter, RHY, and Dahlberg, AA (1983) Changing occlusal variation in F‘ima Indians. Am. J. Beck and his staff for their assistance in Phys. Anthropol. 62:317-324. gathering patient records for this study, Brian Craven, AH (1958)A radiographic cephalometric study of Dunford-Shore for his assistance with comthe Central Australian Aboriginal. Angle Orthod. 2812-35. puter operations, and Rita Kuehler for typing several drafts of this manuscript. This Downs, JF (1972)The Navajo. New York Holt, Rinehart and Winston, Inc. work was supported by NIH BRSG funds to Downs, WB (1948)Variations in facial relationship, their R.Z. German and R.J. Smith. significance in treatment and prognosis. Am. J. Orthod. 34:812-840. 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