Karo Batak Cousin Marriage, Cosocialization, and the Westermarck Hypothesis

Among the Karo Batak of North Sumatra, Indonesia, marriages between matrilateral cross cousins (impal) are the ideal, yet rarely occur. Further, ethnographic accounts reveal a stated aversion to impal marriage. These observations are consistent with Westermarck’s “negative imprinting” hypothesis if impal are cosocialized. We present analyses of postmarital residence patterns from two studies of the Karo Batak. The analyses reveal that although individuals are likely to have been raised in close propinquity with some impal, cosocialization rates were probably not high enough for classical Westermarckian phenomena alone to account for the rarity of impal marriage. In accord with Westermarck’s speculations on the origins of taboos, we propose a hybrid explanation combining evolved inbreeding avoidance mechanisms and their cultural by-products and generalize our findings to a model of cosocialization given cousin type and residence patterns.