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As an owner of a human spine you may become interested in its design features and common problems as time and wear draw your attention to it. The basic structure is one of blocks of hard bone alternating with disk of soft cartilage. For millions of years this design has provided strength and flexibility for four-legged animals satisfactorily, in part because the load is evenly spread horizontally over each disk, and in part because most animals die before they get a chance to wear out.
By contrast humans use this design in a vertical position with the effect that each disk and vertebra must endure its own share of the load as well as the load of everything above it. Secondly in advanced economies, humans usually get a chance to wear out before they die. These two factors make disk problems common in middle-aged humans.