Fetal behavioral development and brain growth in Chimpanzees versus humans: A view from studies with 4D ultrasonography

Abstract

This chapter initially describes how to perceive the relationship between individual development and evolution, then examines the essential nature of heterochronic evolution in humans and chimpanzees, the closest relative of humans, by comparing their fetal behavioral and brain development. We discuss the results of our recent studies on human and chimpanzee fetuses by using four-dimensional ultrasonography. Results 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 or deceleration in the increase of growth velocity of brain volume among species crucial to clarify how much earlier human infants are born and how retarded is the development of their postural reactions is. Accumulated data suggest that further verification of temporally modified growth and development among species will help us to understand the effect of individual development on the evolution of human behavior.