Dermatoglyphic Analysis of Total Finger Ridge Count in Female Monozygotic Twins Discordant for Sexual Orientation

Journal of Sex Research, Nov, 2000 by Lynn S. Hall

In the analysis of twins discordant for sexual orientation (study groups), the homosexual twin was always placed in the X category because they always had the highest Klein grid scores, and the heterosexual cotwin was always placed into the corresponding Y category because they always had the lowest Klein Grid scores. Among twins concordant for sexual orientation (control groups), it was important to place the twins into a category based on an empirical and consistent criteria, since statistically significant results could be artificially obtained as a result of biased categorization. To avoid this problem, twins concordant for sexual orientation were placed in X or Y categories based on the same criteria used for twins discordant for sexual orientation. Therefore, the twin with the higher Klein Grid Score was assigned the X value, and the twin with the lower score was assigned the corresponding Y value. The Klein Grid was used as the primary measure largely because of the difficulty of assigning twins who are concordant for sexual orientation to groups using the same criteria as that used for the twins discordant for sexual orientation. Although all of the cotwins in the control groups were homosexual, the Klein Grid scores are usually slightly different. However, in the event that a set of twins had identical Klein Grid scores, the Kinsey scores were used to determine the group into which the twin was placed.

Wilcoxon tests were computed for total finger ridge count (TFRC). To calculate the Wilcoxon test for TFRC, the sum of all the ridges on the finger tips of both hands was determined for each of the twins.

RESULTS

Initially, 15 sets of twins responded to the advertisements and were interviewed. The sample is described elsewhere (Hall, in press). Table 1 shows the results for TFRC for 7 sets of female twins discordant for sexual orientation (the study group). All of the twins with the higher Klein Grid scores (homosexual females) had lower ridge counts than the cotwins with the lower Klein Grid scores (heterosexual cotwins). The resulting Wilcoxon (T = 0) was statistically significant with an n of 7 (p [is less than or equal to] .01).

Table 1. Wilcoxon Rank Sum Analysis for Total Finger Ridge Count (TFRC) in Twins Discordant For Sexual Orientation (Study Group)

[X.sub.i]      [Y.sub.i]
TFRC             TFRC        Sign of     Difference    Rank of
twin with      twin with    difference   (Xi - Yi)    difference
high Klein     low Klein
Grid score     Grid score

 43                61           -            18          3
133               153           -            20          4
142               196           -            54          7
 46                76           -            30          5
 98               135           -            37          6
 60                65           -             5          1.5
162               167           -             5          1.5

Note. TFRC: [SR.sub. ] = 0; [SR.sub.-] = 28; T = 0; n = 7; (p < .01).

Table 2 shows the results for TFRC for 5 sets of female twins concordant for sexual orientation (the control group). In one set, the twin with the higher Klein Grid score had a lower TFRC than the cotwin with the lower Klein Grid score. In the other 4 sets, the twin with higher Klein Grid score had a higher TFRC than the cotwin with the lower Klein Grid score. Although it is possible to get significant results with an n of 5, in this case the resulting Wilcoxon (T = 4) was not statistically significant.