We can think of the human baby in its first few years as a living example of some ofthese physical changes taking place. At birth, the baby’s brain is only a quarter of itseventual weight and the larynx is much higher in the throat, allowing babies, likechimpanzees, to breathe and drink at the same time. In a relatively short period oftime, the larynx descends, the brain develops, the child assumes an upright postureand starts walking and talking