Intra-Uterine Selection by the ABO Incompatibility of Mother and Foetus

With the Japanese materials consisting of 2, 709 families with 6, 360 children, the author examined the selective effect caused by the ABO incompatibility of mother and foetus. Attention was focused on the O×A and O×B matings. It was revealed that there actually exists a considerably strong selection and a shortage of children of certain groups from the incompatible matings. As the cause of such elimination of children two different ways of selection could be suggested; the one is at the time of fertilization and the other is by the incompatibility after fertilization. If the gene frequencies of blood groups in population would remain constant independently of each generation, it could also be surmised that mutations were occurring to compensate the losses of gene due to the selection.