[Population genetics and etho-historical considerations of the uniqueness of the Prasun Kafirs and the Kalash (central Hindu Kush) with regard to the ABO blood group system].
An attempt has been made to interpret the quite rare distribution pattern of ABO blood group genes (p > 0.5000, q < 0.1000 and r < 0.5000) among the Prasun Kafirs and the Kalsh of the central Hindu Kush from the point of view of population genetics and ethnohistory. If we consider the different age groups of the Prasun sample it will be observed that there is a marked increase in the frequency of blood group gene A and a corresponding decrease in blood group gene O as we proceed from older to younger age groups. These changes cna be readily explained on the basis of a prenatal selection through mother-child incompatibility. Because of the relatively small starting value of r < 0.5 a selection takes place against O, resulting in an increase of the blood group gene A. The differences in the gene frequencies among the various age groups are so large that apart from mother-child incompatibility other selective factors may have been involved, as for example the smallpox epidemics in the 1930's and in the beginning of the 1940's. Moreover, significant differences in blood group distribution were secured between the upper and lower valley samples which do not accord with the close marital relationships and the relatively long history of the settlement. It must be assumed therefore that particularly the greater frequency of the blood group gene B in the lower portion of the valley is to be attributed to marital relationships with other Kafir tribes or other ethnic groups (Pathans) which have become more frequent since the islamization at the end of the last century. In the case of the Kalash an age and regional differentiation is only possible to a limited extent. Nevertheless it must be assumed that the extremely high A frequency and the lower O and B frequencies are caused by the same genetic and ethnohistorical factors as it is the case with the Prasun Kafirs.