INTERNATIONAL JOURNALOF ANTHROPOLOGY Vol. 1, n. 4: 349-360, 1986 K. Sharma Department of Anthropology, Panjab University, Chandigarh-160014, India. R. S. Corruccini Department of Anthropology, Southern Illinois University, Carbondale, Illinois 62901, U.S.A. R. H. Y. Potter Dental School, Indiana University, Indianapolis 46202, U.S.A. Genetic and Environmental Influences on Bilateral Dental Asymmetry in Northwest Indian Twins The role of genetic and environmental factors on dental asymmetry (in maximum crown dimensions) was examined using 58 pairs of twins (23 MZ and 35 DZ) from Chandigarh, India. The t'-test for equality of means by zygosity showed only one variable significantly different among 56: this is ascribable to Type 1 error. Heterogeneity of MZ- DZ total variance was observed in 42.9% of traits of the two types (fluctuating and directional) of bilateral asymmetry. In general, MZ twins showed higher total variance than DZ pairs. MZ twins also showed stronger environmental covariance for a majority of the traits. Dental asymmetry measures thus yielded consistently low genetic variance ratios and indicated predominantly complex environmental determinism. Since fluctuating asymmetry is widely believed to be an environmental stress indicator, this data set allows confirmation of methods for detecting unequal environmental influences on the zygo- sities which bias estimates of genetic variance and heritability. Key words: Directional, Fluctuating, Asymmetry, Tooth size, Genetic factors, Twins, India. Introduction Van Valen (1962) coined the term <41uctuating asymmetry~> for differences due to developmental accidents in bilaterally symmetrical structures. The same phenomenon was regarded as <~developmental noiso> by Waddington (1957). These bilateral structures theoretically should develop as mirror images of each other, since it is assumed that the genetic information for both sides is the same (Adams and Niswander, 1967). The degree of asymmetry is assumed to be proportional to the magnitude of local developmental distur- bances. Susceptibility to such interferences is presumably determined by the genetic architecture of the individual, and genomes relatively resistant to these fluctuations are considered to be buffered against the stresses of development and are thus more stable (Mather, 1953). The asymmetry in the size and shape of dental antimeres is a well recognized phenomenon in both man and animal. Animal studies conducted mostly on rodents (Doyle, Kelley and Siegel, 1977; Sciulli, Doyle, Kelley, Siegel and Siegel, 1979; Siegel and Doyle, 1975; Siegel, Siegel, Krimmer, Doyle and Barry, 1977; Smookler, Goebel, Siegel and Clarke, 1973) have related the magnitude of dental asymmetry to environmental factors like heat, cold, noise, etc. Some other studies (e.g., Bader, 1965) have found greater fluctuating asymmetry in the dentition of inbred rodents. In man, consanguinity has been reported to affect the magnitude of dental asymmetry (Bailit, 1966; Niswander and Chung, 1965). Suarez (1974) found greater magnitude of fluctuating dental asymmetry in Neandertal man as compared to a sample of modern Ohio whites. He postulated that Neandertals might have been a highly inbred population. This claim has been contested by Doyle and Johnston (1977) on the basis of their study of inbred samples of Eskimo and Pueblo populations who were found to exhibit dental variance of