Finger ridge-count variability in sub-Saharan Africa

Finger ridge-counts correlate with the second to fourth digit ratio (2d:4d)

OBJECTIVES

This study examines the relationship of finger ridge-counts to second to fourth digit ratio, which has not yet been definitively demonstrated. The related question of sex dimorphism in finger ridge-counts is further elucidated.

METHODS

A sample of Germans, including 1134 males and 1031 females, was examined for sex dimorphism in the finger ridge-counts. Second and fourth digit lengths were measured in a sub-sample of 91 males and 100 females to compute second to fourth digit ratio. Principal component scores were obtained to investigate sex dimorphism and the correlation between ridge-counts and digit ratio. Regression and analysis of covariance were used to investigate relationships.

RESULTS

Males generally have higher ridge-counts than females but subtle dimorphic features emerge from the principal components, such as a contrast between digits 2 and 4, suggesting a ratio analogous to the digit ratio. The most dimorphic feature is digit 1 directional asymmetry, males exhibiting a stronger right bias than females. Digit ratio is significantly related to four principal components, expressing various contrasts among digits. Other relationships involve contrasts between digits 3 and 5 and asymmetry on digit 2.

CONCLUSIONS

This paper provides definitive evidence that finger ridge-counts correlate with second to fourth digit ratio. The most important finding is that associations of ridge-counts with digit ratio do not involve commonly used summary counts over all digits. Rather, associations act more locally, in ways paralleling the digit ratio, in others reflecting asymmetry. The results support the idea that prenatal sex hormones affect finger ridge-counts.

Topological variability and sex differences in fingerprint ridge density in a sample of the Sudanese population

Fingerprints are important biometric variables that show manifold utilities in human biology, human morphology, anthropology, and genetics. Their role in forensics as a legally admissible tool of identification is well recognized and is based on their stability following full development, individualistic characteristics, easy classification of their patterns, and uniqueness. Nevertheless, fingerprint ridge density and its variability have not been previously studied in the Sudanese population. Hence, this study was conducted to analyze the topological variability in epidermal ridge density and to assess the possibility of its application in determining sex of Sudanese Arabs. The data used for this study were prints of all 10 fingers of 200 Sudanese Arab individuals (100 men and 100 women) aged between 18 and 28 years. Fingerprint ridge density was assessed for three different areas (radial, ulnar and proximal) for all 10 fingers of each subject. Significant variability was found between the areas (p < 0.01). Women showed significantly higher ridge density in the three areas for all and each fingers. Men and women showed similar patterns of densities with distal areas being denser than proximal ones. Side asymmetry was more evident in distal areas. Ridge density thresholds for discrimination of sexes were developed. Hence, fingerprints found in forensic examinations/crime scenes can be useful to determine sex of Sudanese individuals based on fingerprint ridge density; furthermore, ridge density can be considered a morphological trait for individual variation in forensic anthropology.

Fluctuating asymmetry in quantitative dermatoglyphic traits: twins and singletons

Fluctuating asymmetry for the digital quantitative value was analyzed in a sample of twins (mono and dizygotic) and singletons. The aim was to check if the influence of twinning on the development is expressed in a higher fluctuating asymmetry in twins than in singletons. The results have shown that significant differences exist among the three groups studied, and these differences are fundamentally expressed when the radial and ulnar counts are considered separately.

A fingerprint characteristic associated with the early prenatal environment

Fingerprints and fingertip ridge counts (RCs) have a significant genetic component. However, they also reflect the nongenetic environment of early pregnancy, an important time window for tissue differentiation and organogenesis. Fingerprints are permanently configured before the 20th week of gestation, and each fingertip's RC is related to the growth and regression of its early fetal volar pads. Rostral and caudal aspects of the embryonic limb bud have different relations to somite segments and to morphogen-activator functions. We hypothesized, therefore, that early fetal circumstances would be associated with a contrast in RCs between the thumb (digit 1) and little finger (digit 5). We obtained RCs from the fingerprints of a sample of 658 Dutch adults identified through prenatal and delivery records of Dutch urban births occurring during 1943-1947, an historical era that included months of wartime disruption with a winter famine. We calculated the mean of left- and right-hand RC differences between digits 1 and 5 (Md15). The Md15 fluctuated in relation to the calendar season of the mother's last menstrual period, but only if the gestation occurred outside of the wartime disruption interval. If the gestation occurred during the disruption interval, the Md15 seasonal fluctuation was not evident. This finding suggests that parental environmental factors may influence the fingerprints of the offspring. Fingerprint RC differences observed in postnatal life may be useful in the study of metabolic or anatomic programming related to the early prenatal environment.

Geographical and ethnic variability of finger ridge-counts: biplots of male and female Indian samples

The graphical technique of biplot due to Gabriel and others is explained, and is applied to ten finger ridge-count means of 239 populations, mostly Indian. The biplots, together with concentration ellipses based on them, are used to study geographical, gender and ethnic/social group variability, to compare Indian populations with other populations and to study relations between individual counts and populations. The correlation structure of ridge-counts exhibits a tripartite division of digits demonstrated by many other studies, but with a somewhat different combination of digits. Comparisons are also made with the results of Leguebe and Vrydagh, who used principal components, discriminant functions, Andrews functions, etc., to study geographical and gender variations. There is a great deal of homogeneity in Indian populations when compared to populations from the rest of the world. Although broad geographical contiguity is reflected in the biplots, local (states within India) level contiguity is not maintained. Monogoloids and Caucasoids have distinct ridge-count structures. The higher level of homogeneity in females and on the left side observed by Leguebe and Vrydagh is also observed in the biplots. A comparison with principal component plots indicates that biplots yield a graphical representation similar to component plots, and convey more information than component plots.

Dermatoglyphic affinities among the Telugu populations with contrasting ethnohistorical backgrounds

Using 22 finger dermatoglyphic variables (radial and ulnar ridge counts on each of the 10 fingers, total number of whorls and total number of loops per individual), affinities among the five endogamous populations of Andhra Pradesh with contrasting ethnohistorical backgrounds were examined. The samples constitute rolled fingerprints of 1,334 individuals of all ages, 736 males and 598 females, and were drawn from the three southern districts of Andhra Pradesh. Univariate analysis of variance, cluster analysis of Mahalanobis' D² -values, and stepwise discriminant analysis were employed to study the extent of population heterogeneity and nature of relationships among them. The observed dermatoglyphic affinities conform to the known ethnohistorical and geographical backgrounds. The smallest set of 9 most discriminating variables gives the best configuration expected under ethnohistorical backgrounds. Addition of more variables, although further augmenting the dispersion among the group centroids, distrots the picture of known ethnohistorical relatiohships. © 1992 Wiley-Liss, Inc.

Characterization of digital dermatoglyphic features in Salazar Valley: comparison with other Basque valleys

Digital dermatoglyphics of a sample from the Basque Valley of Salazar, situated in the West of the Pyrenees, were analysed. The results showed bimanual differences in both sexes, and also sexual differences for both hands. The comparative study with other Basque valleys showed that, in spite of their supposed common origin, the geographic barriers and the isolation have generated a genetic/dermatoglyphic and linguistic differentiation.

Dermatoglyphic analysis of autistic basque children

We have analyzed the digital and palmar dermatoglyphics in a sample of autistic children from the Basque Country. The results have been compared with those from a control sample having the same characteristics relative to the ethnic region. We found significant differences between the digital dermatoglyphics of autistic boys and control boys. Autistic children have a higher frequency of transitional radial loops and a lower frequency of dicentric whorls; also the total finger ridge count (TFRC) and radial count are lower in autistic individuals. There were no significant differences in the girls. In palmar dermatoglyphics, autistic girls have a lower frequency of radial loops in the hypothenar area, and the value of the "atd" angle is higher than in control girls. These differences were significant. The a-b interdigital ridge count is significantly lower in autistic boys. Autistic children of both sexes have a higher frequency of aberrant palmar creases. The results obtained in the present study do not contradict the hypothesis that genetic factors may be important in autism of unknown cause.

Finger ridge count in Basque populations: univariate and multivariate comparison with other Spanish populations

We have analysed finger ridge counts in the indigenous Spanish Basque population (841 males and 911 females). Bimanual and sexual variation have proved to be statistically significant. The results in the Basque population were compared with those of other Spanish populations. In the univariate comparison statistically significant differences appear. The means found in the Basque population are the lowest. Our population is situated on the lower part of the variation range of the European populations for whom data are available. In principal component analysis the first two components explain more than 90% of the total variability. The first component is interpreted as a size component, which is usual. The factor scores of the individual samples have proved to be very useful in showing which populations are nearest to the Basque one.

Associations between dermatoglyphic variation, topography, and climate in Kenya

Correlations between a number of dermatoglyphic finger and palmar taxonomic traits relating to 57 male and 53 female Kenyan populations, and altitude and mean annual rainfall are significant, not only in terms of the full range of samples, but also when samples are divided into independent smaller groups. These results are discussed and contrasted with those of other studies which have found no relationships between dermatoglyphic variation and climate in sub-Saharan Africa.

A comparison of dermatoglyphic methodologies in population studies

Use of dermatoglyphics in population studies has been marked by a great deal of methodological variation among investigators. We compare various dermatoglyphic approaches using data derived from four groups in the Kumaon region of India. Dermatoglyphic data included ridge-counts and other quantitative variables, and the classification systems of Cummins and Midlo and Penrose and Loesch. Results were evaluated against anthropometric and serological relationships. No clearly superior approach emerges, although it is generally true that palmar variables exhibit more intergroup heterogeneity than digital variables and produce more reasonable results than the other approaches. The conventional method of treating ridge-counts, that of choosing the larger of the two counts, was the most unsatisfactory of the quantitative approaches, leading to the recommendation that both radial and ulnar counts be retained. We conclude that environmental variation may contribute substantially to intergroup variation.

Components of racial variation in finger ridge-counts

Principal components analysis was used to evaluate finger ridge-count variability as an indicator of genetic relationships between populations. The analysis was carried out on American White, American Black and African Black samples, each including both sexes. Each individual is represented as a vecotr of 20 counts, a radial and an ulnar count for each digit. No assumptions were made prior to analysis concerning the number of meaningful components, and all were examined sequentially. The first five eigenvectors extracted from the within-groups correlation matrix have loadings very similar to those previously described by Roberts and Coope ('75). However, it is the component scores derived from the sixth eigenvector which show the most marked variation, accounting for 45% or more of the D2 in all Black-White comparisons. A number of other components also show significant intergroup heterogeneity, but they often do not accord with what is known of the genetic relationships between the populations. Apparently a large amount of ridge-count variation is not genetically meaningful, at least as far as these populations are concerned.