The vertebral column--a phylogenetic failure? A theory explaining the function and vulnerability of the human spine.

The increase in degenerative diseases of the vertebral column is often attributed to an inadequate adaptation to the upright posture in the human. On the basis of a precise analysis of the motion segments, an attempt has here been made to demonstrate that the design of the vertebrae in both the larger mammals and in humans has resulted in no qualitative differences between the stresses to which either is subjected. In the course of evolution there has certainly been an obvious conflict in aims between the need for essential stability and the desired or necessary mobility. These mutually self-limiting mechanisms are reflected in the highly specialized architecture of the ligamentous apparatus and vertebral joints. We conclude that the human vertebral column seems to be an optimized compromise of evolution.