MATERNAL CRADLING AND INFANT NIPPLE PREFERENCES IN RHESUS-MONKEYS (MACACA-MULATTA)

This study investigated lateral biases in nipple preferences, maternal cradling, carrying, and retrieval in 41 rhesus macaque (Macaca mulatt a) mother-infant dyads living in two captive social groups. Observatio ns were made during the first 6 weeks of infant life using a combinati on of scan sampling and ad-libitum sampling techniques. Infants exhibi ted a significant left-nipple preference in the first weeks of life bu r the bias decreased with infant age. Mothers showed a left-arm bias i n carrying their infants bur no significant lateral bias in cradling o r retrieval. Our results suggest that the left-side cradling bias repo rted in studies of humans and some other primates reflects a bias in t he infant's nipple preference lather than in maternal behavior. The in fants' preference for the left nipple is consistent with both Salk's ( 1960) heartbeat hypothesis and with more recent hypotheses linking thi s lateral bias with brain asymmetry and hemispheric specialization for mother-infant communication. (C) 1998 John Wiley & Sons, Inc.