Finger ridge-count variability in sub-Saharan Africa.

Mean finger ridge-count data were obtained, primarily from literature sources, for 31 male and 24 female sub-Saharan African samples. The 10 finger ridge-counts and total ridge-count were used as independent variables in a multiple regression analysis, latitude and longitude serving in turn as the dependent variables. The results show that it is not the magnitude of the ridge-counts themselves that is important, but rather contrasts between groups of digits. The most important geographically patterned variation in ridge-counts consists of contrasts between digits 4 and 5 and digits 2 and 3. South and south-east African populations are characterized by low contrasts, west Africans by high contrasts and, south-west Africans are intermediate. The geographical patterning of the contrast agrees well with known patterns of gene flow into and within the continent as determined by serological genes. Principal components analysis was also carried out to determine whether within-group components corresponding to the geographically relevant between-group variation could be identified. The third, fourth and fifth components drew the same types of contrasts between the groups of digits identified in the multiple regression analysis, but they were relatively unimportant. The geographically important principal components would have been overlooked in a traditional multivariate analysis of finge ridge-counts, since the analysis would have been dominated by pattern size. We conclude that finger ridge-counts are potentially very useful in population studies, but account must be taken of their multicomponent nature.