Finger Ridge-Count Variation among African Rainforest Hunter-Gatherers: Implications for Origins and Diversification

Dermatoglyphic studies of traditional rainforest hunter-gatherers (RHG) have a long history, but as yet no one has synthesized the available data to develop a coherent picture of RHG relationships to one another and to their agricultural (AGR) neighbors. This has been due in part to absence of comparable data, which has now been remedied by the late H. Brehme of Freiburg University, who counted ridges and classified patterns on existing prints, mostly collected in the early 20th century. Thus, analyses of dermatoglyphic prints from most African RHG groups, done in the same way by the same observer, now exist. The present analysis uses finger ridge counts to examine the structure of RHG and AGR populations. Eastern RHG and some AGR samples come from the eastern Democratic Republic of the Congo, some eastern AGR samples are from Kenya, and western RHG and AGR samples come from Cameroon and adjacent countries. Statistical procedures include analysis of variance (ANOVA), multivariate analysis of variance (MANOVA), analysis of covariance, and canonical variates obtained from the discriminant procedure. The relationship of ridge counts to adult stature was also examined. Eastern and western RHG are clearly differentiated on ridge counts. Eastern RHG are differentiated from their AGR neighbors by virtue of very low ridge counts, but western RHG have higher ridge counts, more in line with their AGR neighbors. MANOVA results reveal significant variation among groups and sexes, as well as variation among groups in sex dimorphism. Beyond the marked differences between eastern and western RHG, the western AGR show a certain cohesion, but eastern AGR are highly dispersed. Variation in sex dimorphism involves primarily eastern and western AGR groups. Ridge counts also correlate with stature, suggesting that short stature has prenatal origins. The general conclusion is that ridge-count variation supports a difference between eastern and western RHG seen in cranial morphology and genetics. The unanswered question is why eastern RHG, with the lowest ridge counts in the world, are so differentiated. Variation in sex dimorphism, especially among the AGR neighbors, implies different responses to prenatal hormones. Ridge counts demonstrate variation in prenatal development, which is still poorly understood. Genes influencing limb and digit development have been identified, which along with postnatal anthropometric and disease associations provide a basis for future development and testing of hypotheses.