Showing papers on "Fluctuating asymmetry published in 1982"

Fluctuating asymmetry of dental morphological traits: new interpretations.

Abstract: The analysis of the amount of antimere asymmetry for two dental morphological traits, Carabelli's and protostylid, reveals that it cannot be regarded simply as a monitor of environmental stress. The fluctuating asymmetry noted and the methods used in reporting it suggest that the results are dependent on scoring methods, sample sizes and total trait frequencies. The amount of fluctuating asymmetry also appears to be dependent on the duration of the development of the trait and, generally, increases as one goes distally from the deciduous second molar in the total molar field. Metric fluctuating dental asymmetry has been used as a measure of the developmental stability of various living and prehistoric human populations (Bailit et al. 1970; Perzigian, 1977; Harris and Nweeia, 1980). It is generally assumed that this asymmetry reflects response to environmental stress (DiBennardo and Bailit, 1978). Recently, attention has been directed to comparing the magnitude of dental nonmetric trait asymmetry in different populations (Baume and Crawford, 1980). Few workers have published observations on the frequency of morphological traits on antimeric teeth. Normally, only left side trait expression has been recorded. Those who have noted antimeric trait expressions, generally ascribe any asymmetry they find to fluctuating asymmetry, i.e. absence of directional asymmetry. Most workers take the high concordance of trait presence between sides to mean that genetic factors are the same for both sides of the dental arch. A few authors have claimed high levels of bilateral asymmetry for certain dental morphological traits. Meredith and Hixon (1954) stressed that in their sample there was a noticeable difference in the size and presence of Carabelli's cusp between the two sides of the dental arch. Biggerstaff (1973), in a study of concordance for Carabelli's trait between twins, noted a low concordance for antimere comparisons within individuals. Harris (1977) found relatively high levels of asymmetry for a variety of nonmetric dental traits in several Melanesian populations. department of Anthropology, McMaster University, Hamilton, Ontario, Canada. 2Faculty of Dentistry and Department of Anthropology, University of Toronto, Toronto, Ontario, Canada. Human Biology, December 1982, Vol. 54, No. 4, pp. 789799. © Wayne State University Press, 1982 This content downloaded from 157.55.39.107 on Wed, 30 Mar 2016 06:23:57 UTC All use subject to http://about.jstor.org/terms 790 Shelley R. Saunders and John T. Mayhall Townsend and Brown (1981) presented asymmetry figures for an Australian Aborigine population. The amount of asymmetry for expressions of the Carabelli's trait was 9.38% in the deciduous second molar and 8.43% in the permanent first molar based on a three-grade expression ranking. What must be clarified when assessing the magnitude of dental trait asymmetry is whether one is recording simply presence-absence asymmetry where the trait appears in any form on only one side of the mouth, or ranked asymmetry where different degrees of trait expression are found on the two sides of the arch. Most workers seem to agree that presence-absence asymmetry rarely reaches higher than 5%, but it is claimed that in populations, total ranked asymmetry varies around 20% for at least one trait, the Carabelli's trait (Scott, 1980). Baume and Crawford (1980) have argued that total ranked asymmetry differences between populations have significant biological implications. It is difficult to assess the validity of these statements from an investigation of the published literature because there is not enough information on presence-absence and total ranked asymmetry for a variety of traits and populations. The present study was undertaken to assess the magnitudes of these two measures of asymmetry in both deciduous and permanent teeth of a large population sample with the intention of assessing developmental differences in asymmetry production. During the course of the data analysis it was determined that the presently accepted method of recording asymmetry for nonmetric traits is inappropriate and may lead to biased results. Materials and Methods Approximately 1100 individuals comprise a sample of parents and children who took part in the Burlington Growth Study from 1953-1974. A series of dental casts taken at regular intervals for each child and a single set of casts for each parent were available. Thus, for the children we could observe nonmetric trait presence on deciduous and permanent teeth of the same individual. Coming from a single small town of 8500 people, the Burlington sample is representative of many Canadian towns in terms of family size, educational level, income and age (Popovich, 1959). Approximately 80% of all parents of the children traced flieir ancestry to the British Isles. Antimeric maxillary and mandibular molar teeth of individuals were compared for the presence and expression of two morphological traits, Carabelli's trait and protostylid. The traits were scored using standard This content downloaded from 157.55.39.107 on Wed, 30 Mar 2016 06:23:57 UTC All use subject to http://about.jstor.org/terms Asymmetry of Dental Morphological Traits 791 models prepared by Dahlberg (1956) and Hanihara (1960) with constant reference to these standards for consistency by a single experienced investigator (Mayhall et al. 1982). The grades of observation for the Carabelli s trait were (1) absent, (2) single furrow, (3) Y, (4) double furrow, (5) bulge, (6) small cusp, and (7) large cusp. For the protostylid, they were (1) absent, (2) buccal pit, (3) distal deviation of buccal groove, (4) furrow, (5) prominence, (6) prominence with groove, (7) small cusp, and (8) large cusp. The proportions of asymmetry in the total sample for each trait were recorded according to the method described by Scott (1980) where one observes the percentage of individuals exhibiting a rank difference of 0, 1, 2, or 3 or more grades of asymmetry, the total frequency of these degrees of ranked asymmetry and the frequency of presence-absence asymmetry. The same observations were analyzed a second time with those individuals who were bilaterally symmetrical for trait absence removed from the asymmetry calculations. Finally, comparisons were made of the degrees of asymmetry for the traits between the deciduous second molar and the three permanent molars.

Interpopulation variation in fluctuating asymmetry of the palmar A-B ridge-count

Abstract: Fluctuating asymmetry was measured by the Pearson correlation coefficient between a-b ridge-counts of the right and left hands. Such data were available for 38 samples, which were grouped by major geographical regions. Significant heterogeneity exists within some of the geographical groups but the between geographical group component is highly significant in both sexes. Our results show that a sizable fraction of variation in fluctuating asymmetry is related to geographical race. There is no evidence that it follows environmental or ecological lines. The variation between geographical races suggests that there is a genetic component in the magnitude of fluctuating asymmetry.