Temporal reorganization of growth and development in terms of evolution of human behavior: Implication of interrelation of behavioral development in posture, locomotion, object manipulation, and mutual engagement between mother and infant

Abstract

I first discuss the developmental and evolutionary implications of the temporal reorganization of individual development in human infants, which have resulted in unique human characteristics during early development and child rearing, for example, (1) the large size of neonates, (2) “trade-off” in mother-infant interaction, (3) self-contact behaviors, (4) various manipulations of objects, and (5) emergence of “childhood” and caregiving by multiple caregivers. I also discuss the results of our recent study on human and chimpanzee fetuses by using three-dimensional ultrasonography; this study showed that the growth velocity of the brain volumes of chimpanzee fetuses does not accelerate during late pregnancy, whereas that of human fetuses does accelerate through late pregnancy. Additional analysis and findings show that the timing of cessation in the increase of growth velocity of brain volume among species is crucial to clarify how much earlier infants are born and how retarded is the development of their postural reactions. Previously accumulated data suggest that further verification of temporally modified growth and development among species will help understand the effect of individual development on the evolution of human behavior.View full abstract