Dental asymmetry as a measure of environmental stress in the Ticuna Indians of Colombia.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 53:133-142 11980) Dental Asymmetry as a Measure of Environmental Stress in the Ticuna Indians of Colombia EDWARD F. HARRIS AND MARTIN T. NWEEIA Department of Orthodontics (EEH.),and School of Dental Medicine (E.F.H., M.T.N.), University of Connectccut,Farmington, Connecticut 06032 KEY WORDS South America Odontology, Asymmetry, Amerindians, ABSTRACT The magnitude of fluctuating dental asymmetry is reported for a marginally Westernized, horticultural Indian group, the Ticuna of the Region Amazonas, Colombia. Asymmetry is lower than in other Amerindian and Eskimo groups reported to date, which accords with the adequacy and reliability of traditional food sources and complements the claim that protein intake is a t or above minimum requirements. Partitioning the variation by sex, arcade, dimension, and tooth discloses several statistically significant effects. Among these: 1)females are proportionately more asymmetric than males; 2) maxillary teeth are more asymmetric than their mandibular counterparts; 3) the mesiodistal dimension is less canalized than buccolingual width in the maxilla, but is more asymmetric in the mandible; and 4) the pattern of asymmetry corresponds closely with the morphogenetic gradients within each tooth field, suggesting that bilaterality provides an additional measure for disclosing underlying genetic and ontogenetic patterns in the dentition. Several approaches are aimed a t assessing the biological effects of different environments on individuals and/or populations. Demographic, epidemiologic, and physiologic parameters each measure how a group is coping with its environment (e.g., Damon, '74). Another approach, and the one used here, is to quantify the degree of developmental stability exhibited by a population sample. The issue is that paired organs (or tissue systems) are seldom exactly symmetric, even though the genetic information is presumed to be (Waddington, '42, '57; Lerner, '54;Rendel, '67). The cause of asymmetry is generally referred to the idiopathic category "stress," since few studies on karyotypically normal humans have access to quantified nutritional or epidemiologic histories, and because the biologic response is non-specific (Hinkle, '73).Attempts a t relating the degree of asymmetry to specific agents in humans have not been successful (e.g., DiBennardo and Bailit, '78). "Stress" incorporates a multitude of inherent and extrinsic agents, including genetic and chromosomal disharmonies, nutritional deprivations, and diseases, infectious and otherwise (Cannon, '32; Selye, '76). Localized side differences in the degree and duration to which growth is retarded by physiological entrench- 0092-948318015301-0133$02.00 G 1980 ALAN R. LISS. INC. ment to the stress condition will result in bilateral asymmetry. Asymmetry is a host response. Heat, cold, and audiogenic stress, pre- and/or postnatally, each produce increased levels of dental asymmetry in rats (e.g., Sciulli et al., '79). Wild and random-bred animals are more symmetric than are inbred strains (e.g., Sumner and Huestis, '21; Bader, '65; Boesiger, '731, and asymmetry can be increased or decreased by selection (e.g., Mather, '53; Waddington, '601, though human studies (Bailit et al., '70; Potter et al., '76) find no evidence of a genetic component. Within an individual, some features are inherently more variable than others (Pearson and Woo, '35; Schultz, '37; Van Valen, '62; Jolicoeur, '63). As part of a descriptive odontometric study of a South American Indian group, the Ticuna of the Region Amazonas, Colombia (Harris and Nweeia, '801, we have assessed dental asymmetry, which we report here. In addition to broadening the narrow baseline of comparative data on dental asymmetry in preliterate groups, the Ticuna are of interest as representatives of the technologic and sociocultural stage encountered throughout the history and much of the prehistory of northern South Received July 27, 1979; accepted February 4, 1980. 133 E.F. HARRIS AND M.T. NWEEIA 134 America outside the areas of cultural florescence (e.g.,Steward and Faron, '59; Willey, '71). In addition, a different statistical approach is used for the study of asymmetry, one which circumvents the inefficiency and the multiple comparisonproblem involved in using variance ratios (e.g., Garn et al., '66a, b; Doyle and Johnston, '77) or intraclass correlations (Bailit et al., '70). The factorial analysis of variance design described below provides a unified approach for the examination of asymmetries by tooth, tooth dimension, arcade, and sex. THE TICUNA Tribes speaking Ticuna (or Tukuna, T i k u n a b a n unaffiliated language possibly related to Arawakan (Mason, '50)-are distributed in and around the intersection of Peru, Brazil, and Colombia. The people live in scattered, semi-permanent, kin-based villages similar to other tropical-forest farming groups of north-central South America (e.g.,Steward, '48; Steward and Faron, '59). The Ticuna are best known ethnographically from the works of Nimuendaju ('48, '52) and Medina ('77). The specific village studied, Arara, about 30 km northwest of Leticia, Region Amazonas, was formed in 1969 as a result of non-Indian coercion from a kin-based unit of a village located in northern Amazonas, adjacent to Brazil. The Ticuna of Arara have access to Western foodstuffs and medical attention (e.g., Medina, '77). Importantly, though, all individuals examined spent their childhood-when crown tooth formation was completed-in an isolated, essentially traditional setting. The Ticuna are horticulturalists, raising primarily platano, yucca, and maize. Fishing provides an important dietary component, but mammals are scarce and hunting contributes little to protein intake. Collecting wild, seasonally available fruits and roots adds substantially to the diet. Data on similar rain forest tribes suggest both that calorie intake (Johnston e t al., '71) and protein consumntion (Chagnon and Hames, '79) are above daily nutritional requirements. Medical examinations of the Ticuna were not conducted. Presumably, they are exposed to a similar spectrum and intensity of problems found in other lowland forest groups. Examinations of a similar group, the Xavante of Brazil, reported by Neel et al. ('64, '67) and Weinstein et al. ('67),emphasize stresses of repeated infections and parasitizations. Neel et al. conclude that, "Physical examination reveals a group which is superficially healthy. The greater evidence of disease in women (lower hemoglobin levels, more common palpable spleens and livers, and soft systolic murmurs) than in men may reflect not only the heavier demands on the women but also the fact that their mode of life results in greater exposures" (Neel et al. '64:128). Insofar as their findings are remesentative of the physical conditions i f other-Indian groups inhabiting virtually identical cultural and natural settings, expectations are that the magnitude of fluctuating dental asymmetry ought to be fairly high by contemporary Western standards, and that a sex difference ought to exist, with females being more asymmetric, on average, than males. MATERIALS AND METHODS Full-mouth dental study models of 57 Ticuna adults (17 to 30 years of age) were measured for maximum mesiodistal (MD) and buccolingual (BL) crown diameters of all permanent teeth (Moorrees, '57) not noticeably affected by attrition, caries, or the like (Harris and Nweeia, '80). The sample has no known bias; cooperation was complete, and only essentially edentulous individuals were omitted. The size difference between left and right antimeres (d = L - R) is used as the measure of asymmetry (Parsons, '64; Garn et al., '66b, '67b). Summary statistics of d provide sample estimates of mean asymmetry and its variability, as well as a test for directional differences (e.g., a negative sign denotes right antimere larger than left). For the analysis of within-group distributions of asymmetry (but not for the inter-group comparisons),the data are transformed to eliminate size differences among teeth. The side difference, d, is divided by the mean size of the left and right teeth. In addition, the absolute value is taken to preclude positive and negative values canceling one another, d" = IL-R( L+R 2 Our rationale is that a given amount of asymmetry in a small tooth pair is of more biologic importance than the same amount in a large pair, when the asymmetries are compared one to another. Likewise, when using d = L - R, other sources of variation in crown size, such as individual, sex, and population differences, may enter into the variance statistic. RESULTS AND DISCUSSION Results are divided into two sections, first a consideration of the degree of asymmetry presented by the Ticuna relative to published re- 135 TICUNA DENTAL ASYMMETRY the buccolingual dimension, Ohio Whites < Eskimo < Ticuna < Puebloans. Consequently, the Ticuna exhibit less asymmetry, on average, than either the Puebloan agriculturalists or the specialized Eskimo hunters. All three of these groups exhibit degrees of asymmetry far in excess of contemporary American Whites. ports of other groups, and second, an analysis of the within-group distributions of asymmetry. Table 1presents summary statistics of d for the Ticuna. In none of the 64 cases is the mean of d significantly different from zero. Moreover, nod is even as large as the standard deviation, so there is no indication of preferential development of any tooth dimension on either side of the midline (i.e., no directional asymmetry). Similarly, the overall distribution of positive (31/64)and negative (33/64)signs of the means is effectively that expected, assuming equal odds. The major source of variation is, then, attributable t o random side differences, i.e., fluctuating asymmetry (Van Valen, '62). 2. Differences within the Ticuna Three considerations have prompted us to examine the within-sample distribution of asymmetries in more than usual detail: 1)laboratory experiments by Siege1 and Doyle ('75) suggest that maxillary and mandibular teeth may respond differently to a given stress; 2) sex and population differences in the length-width ratio of teeth (e.g., Garn et al., '67b; Rosenzweig, '70) and the modest association between length and width (r' = .26, Garn et al., '68) suggest that the two dimensions may respond differently to stress; and 3) cultural and medical features of the Ticuna and similar tropical forest farming groups (Steward, '48) suggest that sex differences may be present in the degree of asymmetry. A three-way analysis of variance (Model I), with the three factors being sex (male, female), arcade (maxilla, mandible), and tooth (11,12,C, P1, P2, M1, M2, M3), is used to circumvent multiple comparison problems and to increase the degrees of freedom (Sokal and Rohlf, '69; Steel and Torrie, '60). Again, data are the transformed antimeric differences d" defined above. 1 . Inter-group comparisons Table 2 presents the statistics for d, with sexes pooled, for the Ticuna and three comparative groups: contemporary American Whites (Garn et al.,'66b, '67a), prehistoric Hopi Indians from Arizona, and prehistoric Alaskan Eskimo (Doyle and Johnston, '77). Differences in the magnitude of fluctuating asymmetry between the Ticuna and each of the other three groups are determined from the ratio of variances. Most of these F-ratios (43/68, 63%) are statistically significant. The four groups can be sequenced relative to their degree of fluctuating asymmetry by ranking the variances of the groups for each tooth and then calculating the mean ranks. The sequence for the mesiodistal dimension is: Ohio Whites < Ticuna < (Puebloans, Eskimo). For TABLE 1 . Summary statistics of asymmetry, d', of mesiodistal and buccolingual diameters (mmi of Dermanent teeth o f the Ticuna. Mesiodistal Tooth Buccolingual MalesZ Females Males n X X n X S n 21 24 26 24 26 24 25 10 ,026 -006 -.058 -019 -.092 -.073 -222 -.375 24 24 27 26 24 19 15 -.038 .027 ,046 .048 ,102 S n S Females X S Maxilla I1 I2 C P1 P2 M1 M2 M3 .219 ,292 ,320 ,365 .382 ,378 ,430 ,590 14 15 25 23 26 19 22 4 -.046 .545 ,163 ,411 -.084 ,237 ,211 .445 .123 ,449 -.132 ,440 ,018 .823 -.213 1.260 23 23 26 25 26 23 25 15 .026 ,013 ,033 -.OOO p.173 -.072 -.064 -.347 ,280 ,487 ,341 ,416 ,621 .313 ,723 .448 16 16 23 24 26 20 22 ,215 ,191 ,221 ,299 .332 ,066 ,285 -.033 .335 ,337 1.115 23 22 25 24 23 11 13 4 ,000 .030 ,034 ,117 ,089 -.091 ,031 -.050 ,174 .207 ,207 .316 ,374 ,418 ,467 ,385 23 22 26 26 24 19 15 13 -.lo4 -.052 p.056 -.006 -.031 ,050 -.133 ,788 .298 -226 -386 .383 -202 252 ,402 ,992 8 -.037 -.230 -.063 -.la1 p.238 -.155 p.294 .376 514 ,474 ,358 ,404 ,375 ,655 531 21 19 24 25 23 11 13 6 -.052 ,013 ,044 ,138 ,180 -.091 ,108 .267 ,286 209 ,237 ,300 .375 .297 ,396 ,529 p.088 Mandible I1 I2 C P1 P2 M1 M2 M3 8 'd = left-right. See text for additional explanation. %nis number of antimeric tooth pairs (= individuals); Z IS arithmetic mean of d; s is standard deviation of d E.F. HARRIS AND M.T. NWEEIA 136 situation: The arcade-dimension effect is statistically significant (Table 3), and, as shown in Figure 1,there is a difference in the direction of response. While the magnitude of fluctuating asymmetry exhibited in tooth width is subequal in the two arcades, tooth length is more asymmetric than width in the maxilla, and less in the mandible. This finding, again, represents the combined effects of all tooth types. The following results are based on the three-way anovas of asymmetry of the mesiodistal (Table 4) and buccolingual (Table 5 ) crown diameters. Tooth dimension (MD, BL) was omitted from the analysis of variance simply to keep the number of interactions within interpretable limits. Examined by a one-way analysis of variance, pooling tooth type, sex, and arcade, there is no difference in the magnitude of fluctuating asymmetry between mesiodistal and buccolingual dimensions (F = 0.02, with 1and 1,288 degrees of freedom). One interactive effect is tested: An arch-dependent difference in the stress-response of crown length and breadth has been reported in laboratory animals (Siege1 and Doyle, '75). This finding is that upper molar breadth (BL) and lower molar length (MD) exhibit more asymmetry than the alternate dimensions. A test for interaction in the Ticuna Indian sample discloses a similar Main effects. All three variables-sex, arcade, and tooth-exhibit statistically significant differences in the MD dimension. Only TABLE 2. Sample size (n) and variance (sz) ofantimeric differences,d , for the Ticuna and three comparative groups (sexes pooled) and F-ratio tests for differences in the magnitudes o f s 2 between the Ticuna and each comparative group. ~ ~ Tieuna Tooth n Ohio Whites' SZ n F S2 Eskimo2 Puebloansi F n 52 F n 52 42 40 48 .33 .14 .33 .55 .20 2.W 1.3 2.W 1.3 3.4* 26 30 42 42 28 .38 .28 .28 .16 .16 2.3* 1.6 1.7 42 40 48 44 28 .29 .10 27 .66 3.1* 1.3 4.F 1.7 1.3 44 42 48 46 30 .08 .49 22 .40 .31 1.2 3.9 1.9 2.5* 2.8* 32 28 40 38 24 .30 .66 .26 22 .34 2.W 2.4* 2.F 2 2 1.5 26 30 40 40 28 .ll .06 .05 .04 .16 1.4* 4.F 2.5* 12.W 1.4 42 40 48 44 26 .22 .19 .25 .18 .16 1.9 2.1* 3.4* 1.1 4.8* 44 .04 42 48 46 28 .ll 3.01 1.2 1.8 1.2 5.W Mesiodistal Maxilla I1 I2 C P1 P2 M1 M2 M3 35 39 51 47 52 43 47 14 .15 .18 .08 .17 .17 .17 .42 .70 310 289 278 293 272 309 217 47 46 52 50 47 30 28 12 .04 .04 .05 .09 .13 .12 .16 .88 300 312 304 297 261 300 171 .06 .08 .05 .03 .05 .07 .14 2.4* l.e 1.7* 5.W 3.8* 2.5* 2.F 44 34 2.e 4.4* Mandible I1 I2 C P1 P2 M1 M2 M3 .03 .02 .04 .03 .04 .08 .ll 1.5 1.2 1.1 3.W 2.5* 1.6 1.4 50 Buccolingual Maxilla I1 I2 C P1 P2 M1 M2 M3 39 39 49 49 52 43 47 23 .10 25 .17 .15 27 .12 .48 23 113 104 70 105 99 114 51 .05 .I1 .06 .04 .07 .04 .16 2.1* 2.3* 44 41 50 51 47 30 28 19 .09 .05 .10 .12 .09 .07 .16 .76 111 112 98 107 92 111 31 .04 .06 .09 .05 .07 .06 .10 2.1* 1.3 1.2 2.9 4.F 4.W 2.7* 3.W Mandible I1 I2 C P1 P2 M1 M2 M3 *P C 0.05, two-tailed test. Values computed before rounding G a r n et al. '66b, '67a. ZDoyleand Johnston, 1971. 2.e 1.4 1.2 1.6 .13 .19 .15 137 TICUNA DENTAL ASYMMETRY tooth type differences are significant for BL breadths. The analyses of interactive effects also yield different results for the two dimensions. This disparity is in keeping with the low correlation between length and breadth and the lack of correlation between tooth size and asymmetry (Garnet al., '67a). This presumably reflects differences in the evolutionary forces affecting the two crown diameters, though the mechanism remains unclear (e.g., Sofaer et al., '71; LeBlanc and Black, '74; Frayer, '76). Females are significantly more asymmetric in the Ticuna, but just for the MD diameters. Garnet al. ('66b) and Bailit et al. ('70) found no consistent MD sex differences. In contrast, Garn et al. ('67a) found males to be more TABLE 3. Results of the two-way analysis of variance (Model I ) testing for differences in the magnitude of asymmetry (d*) between dimensions (MD, BL) and arcades (maxilla, mandible). Source of variation Treatments Arcade Dimension Arcade-dimension Residual Total D.F. sum of squares Mean square 1 1 1 1,288 1.291 .00832 .00002 ,00593 1.67407 1.68835 .00832 .00002 .00593 .00130 F-ratio 6.41* 0.02 4.5e *P < 0.05 TABLE 4. Results of a three-way factorial analysis of uariance (Model I) for sex, arcade, and tooth differences in bilateral asymmetry (d*) i n the mesiodistal dimensions. Source of variation Main effects Sex Arcade Tooth First-order interactions Sex-arcade Sex-tooth Arcade-tooth Second-order interaction Sex-arcade-tooth Residual Total D.F. sum of squares Mean square F-ratio 1 1 15 ,00874 ,01414 ,06910 ,00874 .01414 ,00461 7.F 12.3* 4.P 1 15 15 .00533 ,00891 ,00429 .00533 ,00059 ,00029 4.F 0.5 0.2 15 .01591 ,66468 .79109 .00106 .00115 0.9 586 639 *P < 0.05. TABLE 5. Analysis of variance table for buccolingual dimensions+. Source of variation Main effects Sex Arcade Tooth First-onler interactions Sex-arcade Sex-tooth Arcade-tooth Second-order interaction Sex-arcade-tooth Residual Total _ _ _ _ _ _ _ ~ *P < 005 +Particulars are as in Table 4 Sum of squares Mean square F-ratio 1 1 15 .00016 .00011 ,05370 .00016 .00011 ,00358 0.1 0.1 2.7* 1 15 15 ,00217 .01101 ,03648 ,00217 ,00073 .00243 1.6 0.5 1.8* 15 587 650 ,01251 .78108 ,89723 ,00083 .00133 0.6 D.F E.F. HARRIS AND M.T. NWEEIA 138 asymmetric for BL diameters. The present findings suggest that the genetic hypothesis that females are better canalized by virtue of their double X chromosome complement may not hold in all populations. Replication of the test using intraclass correlations yields the same results of females being significantly more asymmetric (Nweeia and Harris, '79). Both dimensions exhibit significant arcade differences,which confirms earlier studies that maxillary teeth are more asymmetric (Garn et al., '66b, '67a; Siege1 and Doyle, '75) and complements findings (e.g., Garn et al., '68; Potter et al., '76) that tooth dimensions among the two arcades are largely independent. Mean differences among the eight tooth types are significant in both dimensions. Since Mesiodistal __---Buccolingual ,051 * .04- V c 0 0) 5 .03- Q2- the asymmetry measure d* controls for dimensional differences in overall size, the interpretation is that certain teeth are proportionately more asymmetric. The sex-tooth and arcade-tooth interactions (below)clearly illustrate morphogenetic field gradients for asymmetry, with the pole tooth being developmentally more stable, less asymmetric, in each field. Sex and arcade. These interactions, plotted in Figure 2, are different for the two dimensions. Mesiodistally, the interaction is a difference in magnitude, so, while females are more asymmetric in each arcade, they are disproportionately so in the maxilla. Buccolingually,the interaction constitutes a difference in the direction of response, but is not significant in this series, Sex and tooth. Neither the MD nor the BL interactive effect is significant, as shown by the approximately parallel responses of the two sexes across the eight tooth types (Fig. 3). The association between tooth asymmetry and morphogenetic patterning is evident, both here and in the arcade-tooth interactions (below). The stable tooth in each field is less asymmetric than the others which are also characterized by increased metric and morphologic variability (e.g., Dahlberg, '45;Henderson, '75). The increase in asymmetry from M1 through M3 is particularly apparent. There is no good indication in these resulk (Fig. 4) that later developing teeth are more sexually dimorphic than those, notably I1 and MI, whose crowns are completed during infancy. So, while medical data on technologically and environmentally similar groups Males ----- Females ,051 i 4 .04 .04 U c 0 0) 5 .03- A. Mesiodistal .02J .02 Maxilla Mandible Maxilla Mandible Fig. 2. Plots of interactions between dental arcade and sex for the mesiodistal (A) and buccolingual (B) dimensions. Data (d*) are pooled across tooth types. 139 TICUNA DENTAL ASYMMETRY .09 0. Buccalinpud oe .02J .02 11 I2 C PI P2 MI M2 Ii M3 1'2 c PI Pz MI ~5 Mn Fig. 3. Plots of interactions between sex and tooth type for the mesiodistal (A)and buccolingual (B)tooth dimensions.Sex differencesare primarily of magnitude. The one clear-cut difference in direction, from C to P1for tooth width, probably reflects the lesser variability of lingual cusp size on LP1 among males. IC I , II I I 11 12 C PI Pi! MI Mh Mb Fig. 4. Plots of interactions between arcade and tooth for the mesiodistal (A) and buccolingual (B) tooth dimensions. (Nee1 et al., '64; Weinstein et al., '67) suggest that females would be more asymmetric because of a more debilitating milieu, differences found here are being initiated before sociocultural differences in sex roles are likely to be manifest. Arcade and tooth. The MD lengths of maxillary teeth are consistently more asymmetric than their mandibular counterparts (Fig. 4A), and the slopes are fairly parallel between arcades. Relationships are more variable for tooth widths (Fig. 4B).Neither effect is signifi- 140 E.F. HARRIS AND M.T.NWEEIA cant; the MD difference is, thus, an additive difference in mean asymmetry, while the BL dimension is not sexually dimorphic. Studies that have tested for associations between tooth size and crown morphology (e.g., Dahlberg, '61; Garn et al., '66a; Lombardi, '75) find significant, positive relationships. By extension, the differences among tooth types ought to be interpretable in terms of crown trait variability, and, indeed, this seems to be the case: The BL dimension of upper I2 is particularly asymmetric, and inspection shows.this to be primarily due to variable development of the cingulum. The assertion that I2 is the stable tooth in the mandible (e.g., Dahlberg, '51) is also borne out in these data, where LI1 is more asymmetric than L12 in both dimensions. The canine, well known t o be stable (e.g., Gregory, '22; Garn et al., '62; Grahnen, '62; Hanihara, '76), expresses a moderate degree of fluctuating asymmetry in this sample, with LC being somewhat less asymmetric than UC, perhaps because of the variable occurrence of tubercuZum dentale on the maxillary tooth (Scott, '77). Tooth length exhibits the typical premolar relationship, P1 <P2, in both arcades. Tooth breadth shows the same P1 <P2 relation in the maxilla, and it is not clear why mandibular P1 breadth is more asymmetric than lower P2. Lingual cusp number, for example, is more variable on LP2 (e.g., Kraus and Furr, '53; Turner, '67; Scott, '73). Asymmetry in the molar field is straightforward: M1 <M2 <M3. The maxillary molars are more asymmetric, probably because variability of one cusp, the hypocone, has a major influence on both upper molar length and breadth (e.g., Biggerstaff, '69; Corruccini, '75). It is evident that fluctuating asymmetry is not expressed uniformly across sexes, arcades, or teeth. Sex differences conform to expectation: Females are significantly more asymmetric than males when, as here, asymmetry is expressed as a proportion of tooth size. This difference holds throughout the dentition, from teeth such as I1 and M1, which begin mineralization near birth, through those such as the distal molars, which form in later childhood. This uniformity argues against a simple cultural-environmental explanation that females are stressed more by their roles, though behavioral differences favoring greater female stress are reported for analogous lowland peoples (e.g., Maybury-Lewis, '65; Chagnon, '68; Murphy and Murphy, '74). For example, as adolescents and adults, males spend less time in the village; hunting, fishing, and gardening tend to reduce the risks of parasitism and infectious disease, which are harbored by the village setting. CONCLUSIONS The Ticuna, a lowland forest tribe, exhibit only moderate dental asymmetry. As with other preliterate groups studied to date, their magnitude of fluctuating asymmetry is considerably greater than that of contemporary, technologically advanced groups, but it is significantly lower than in two prehistoric groups used for comparison, Puebloans and Eskimo (Doyle and Johnston, '77). Analyses of the distributions of asymmetry between sexes, arcades, and tooth types affirms the utility of examining the data with a unified statistical approach such as analysis of variance. Females are more asymmetric than males. Maxillary teeth, although morphologically somewhat simpler (at least in the premolar, molar fields), are more asymmetric, especially in the MD dimension. Asymmetry also varies in accordance with tooth position; the stable or pole tooth in each morphogenetic field is least asymmetric. ACKNOWLEDGMENTS We thank R.J. Smith for his helpful discussions and gratefully acknowledge the Explorers Club of New York City for its support. Analysis was conducted under Connecticut Research Foundation grant 35-044 and NIDR grant 1-T32-DE-O70Z7. LITERATURE CITED Bader, R.S. ( 1965)Fluctuating asymmetry in the dentition of the house mouse. Growth, 29t291-300. Bailit, H.L., P.L. Workman, J.D. Niswander, and C.J. 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