Abstract:

Infancy is the first phase of ontogenesis and is the important phase that gives close social bonds to their main caregivers (mostly mothers). In humans, research on behavioral laterality during this early developmental phase is of great significance when exploring the formation and mechanism of brain function asymmetry. Because of similar brain asymmetry with humans, non-human primates were studied. In this paper, previous researches on the behavioral laterality during this early phase were reviewed in non-human primates. Lateral behaviors focused in non-human primates’ early development phase mainly related to limb, nipple and head orientation preference. Limb preference was considered the most obvious index in human and non-human primate brain asymmetry, and has been greatly studied among these three behaviors. Maternal crading and infant nipple preference were also investigated in many studies and neonatal rightward supine head orientation preference was believed to predict later right hand use preference in previous studies. Factors that influenced behavioral laterality including familial inheritance, early-stage differential development between the two cerebral hemispheres, early-stage head orientation preference and the behaviors of main caregivers were discussed. Regarding familial inheritance, both the recessive X-linked theory and the right-shift theory were debated for humans, but no studies reported for non-human primates. In terms of behaviors of the main caregivers, the Valence hypothesis and Right-Hemisphere hypothesis considered that the caregivers’ hemispheres played different roles on regulating different of emotions. The Maternal Handedness hypothesis and Maternal Heartbeat hypothesis were also discussed. We found that selections of individuals, species and behavioral actions were significant problems that stopped any direct comparison among different researches in non-human primates. Therefore, it is recommended that one system investigation on behavioral literalities should be carried out in one species. Comparing results between humans and non-human primates can help us to explain deeply and clearly their differences in behavioral laterality, and provide references for subsequent researches on behavioral laterality during the early development phase in non-human primates and the origin and evolution of human hemispheric specialization.

Key words: Biological anthropology, Brain, Non-human primates, Lateriality