Total finger ridge-count and the polygenic hypothesis: a critique.

The distributions of total ridge count in dermatoglyphic material from Austria and Greece are examined for skewness and kurtosis. The results indicate that total ridge count may not be as useful an example of additive polygenic inheritance as is widely accepted. Following Bonnevie s first assumption (1924), polygenic inheritance of the total ridge-count of the fingers (TRC) by a series of additive genes of independent effect, without dominance and without environmental (i.e. intrauterine maternal) influence is today regarded as established, primarily through the works of Holt and Penrose. To Holt especially we owe a series of meticulous investigations carried out with full knowledge of modern statistical methods. Beginning with the analysis of the frequency distributions of the TRC and the quantitative values of each finger, and examination of the correlation coefficients between the fingers, she went on to study the correlations between parents and children, and between sibs. It was this last study which led to the polygenic hypothesis (Holt 1968, where the original papers are cited). But is this hypothesis really satisfactory? Two decades ago we expressed skepticism (Weninger 1956/57, 1963, 1964), and the issue is worth re ventilation. According to Holt's studies, all the statistical consequences of this hypothesis are fulfilled. The several correlations between parents and children and between sibs are not significantly different from 0.5, the theoretical value calculated by Fisher (1918), when additive genes of independent effect and without dominance are present. Similarly, the mid-parent/child correlation is not significantly different from 0.71 and the regression of children on the mid-parent value is linear, the theoretical expectations under the same conditions according to Penrose (1949). From the similarity of mother/child and father/child correlations, it was conxTo Harold Cummins, pioneer in dermatoglyphic research. 2Institut fur Humanbiologie, Van Swietengasse 1, A1090 Wein, Austria. 3Institut fur medizinische Statistik und Dokumentation, Schwarzspanierstrasse 17, A1090 Wien, Austria. Human Biology , December 1976, Vol. 48, No. 4, pp. 713-725. © Wayne State University Press, 1976. This content downloaded from 157.55. 39.58 on Sun, 31 Jul 2016 05:06:01 UTC All use subject to http://about.jstor. org/terms 714 M. Weninger, G. Ave-Hauser and V. Scheiber eluded that there is no maternal (i.e. intrauterine environmental) effect. Since Holt's publications, the hypothesis of the additive polygenic inheritance of TRC has enjoyed wide acceptance, and there are many papers dealing with TRC as an additive polygenic character. This itself prompts us to reconsider the problem. Undoubtedly the correlations between relatives in Holt's material are in agreement with the theoretically expected values on the hypothesis of additive polygenic inheritance. That means that polygenic inheritance cannot be excluded. But is it proved? We need to ask three questions: (1) is our counting method correct and adequate for the biological background? (2) is the frequency distribution of TRC Gaussian? (3) is the TRC really a uniform and homogeneous character, such that a mode of inheritance can be established? For a long time it has been usual to determine the quantitative value of apical digital patterns by counting the number of ridges between triradius and core, in loops at the side where the triradius is present, in whorls at the side with the higher ridge count. As ridge number is a measure of pattern size and of the size of the fetal digital pad at the time of ridge formation, it is necessary to ask whether these two counts of loop and whorl are equivalent in respect of pad size. We have to remember that the size of a whorl and its pad is given by the distance between the two triradii, whereas the pad of a loop is only sharply defined on one side, the other being more or less flattened. This opinion corresponds with De Wilde's view (1967), that the similar quantitative values in a whorl and a loop do not represent the same biological phenomenon. In order to provide a more correct estimation of pattern size, Wendt (1963) proposed adding to the usual total ridge-count (TRC) an accessory one containing the bilateral ridge number in whorls ("Gesamtleistenzahl"). Occasional authors use this value in their papers, calling it "absolute Leistenzahl" ("absolute ridge-count"). Biologically, ridge number between triradius and core is an estimate of the distance between the border of the pad and its highest elevation. Among whorls the bicentric patterns demand special attention. As in ridge counting of monocentric whorls, two counts (one from each of the two triradii to the closer core) can be obtained. By convention, the higher is taken as the quantitative value. The distance between the two triradii is absolutely ignored. That seems unsatisfactory, as a high number of ridges separating the two cores can be combined with two low counts between the two triradii and their corresponding cores. Stimulated by this discrepancy, we tried to improve ridge counting of This content downloaded from 157.55. 39.58 on Sun, 31 Jul 2016 05:06:01 UTC All use subject to http://about.jstor. org/terms Total Finger Ridge-Count 715 Fig. 1. Counting method of bicentric patterns. Three examples with different distance between the two cores. bicentric patterns by adding the ridge number between the two cores to the conventional count. The ridges between the two cores of bicentric patterns are counted along an imaginary line lying between the respective points of core. Of course, the ridge representing one of the inner centers has now to be included in the new quantitative value (Figure 1). Cummins (1943, p. 75) considered that, in a double-looped pattern, it is "justifiable to create an inner terminus, locating it on a ridge which lies midway between the cores of the two loops; the selection of the point on that ridge will depend on the morphology of the two loops. " Other than this brief allusion, Cummins does not deal further with this problem. Materials and Methods Our investigation is based on the following series, of different origins: 500 male pupils of a "Realgymnasium" at Modling near Vienna (Weninger, 1975) 500 male and 500 female pupils of elementary schools of Vienna (part of the material of Aue-Hauser, 1976) 176 male Greeks (95 normals and 81 with endemic struma) 228 female Greeks (101 normals and 127 with endemic struma), the normal being reported by Weninger and Rothenbuchner, 1974. Two frequency curves of the TRC were calculated from each series; one with the conventional count for bicentric whorls, one corrected by adding the ridge number between the two cores. As the frequency curves of the Greek normals and patients closely resemble each other, they were combined into single distributions, one for the male and one for the female sex. This content downloaded from 157.55. 39.58 on Sun, 31 Jul 2016 05:06:01 UTC All use subject to http://about.jstor. org/terms 716 M. Weninger, G. Ave-Hauser and V. Scheiber