Postural control in man: the phylogenetic perspective.

Erect posture in man is a recent affordance from an evolutionary perspective. About eight million years ago, the stock from which modern humans derived split off from the ape family, and from around sixty-thousand years ago, modern man developed. Upright gait and manipulations while standing pose intricate cybernetic problems for postural control. The trunk, having an older evolutionary history than the extremities, is innervated by medially descending motor systems and extremity muscles by the more recent, laterally descending systems. Movements obviously require concerted actions from both systems. Research in rats has demonstrated the interdependencies between postural control and the development of fluent walking. Only 15 days after birth, adult-like fluent locomotion emerges and is critically dependent upon postural development. Vesttibular deprivation induces a retardation in postural development and, consequently, a retarded development of adult-like locomotion. The cerebellum obviously has an important role in mutual adjustments in postural control and extremity movements, or, in coupling the phylogenetic older and newer structures. In the human, the cerebellum develops partly after birth and therefore is vulnerable to adverse perinatal influences. Such vulnerability seems to justify focusing our scientific research efforts onto the development of this structure.