Let’s start with a brief note on the evolution of the backbone, not in the very beginning, but at the level of the primates. When primates walked on all fours the spine was horizontal (as in dogs, horses, monkeys etc). The spine supported the weight of the various internal organs while the forelegs supported much of the weight of the body. The weight of the internal organs and the actual weight of the spine were supported by the back muscles.Now this is important. Animals struck with a tranquillising dart collapse within minutes as the muscles of the legs and the spine collapse. Although the spine consists of tightly bound vertebrae, which give it great strength, on its own, without the muscles, it is not able to support internal organs (lungs, heart, liver, intestines, etc). Thus the spinal muscles attached to the various parts of the vertebral column of primates had to create a horizontal force that would keep the spine in that position. These muscles acted like steel wires or ropes and just as the weight of the washing is supported by a clothes line, so the weight of the visceral organs is supported by spinal muscles.Let us look at some of the functions of the spine in general and see how the structure of the spine caters to these functions.Human beings walk erect (since Homo Erectus in the evolutionary chain) and, therefore, the vertebrae of the spine become larger in the lower part to facilitate that. Just like the Eiffel Tower or a bamboo stem, which is thin at the top and becomes progressively thicker towards the base, the spinal vertebrae too become increasingly larger at the base of the spine so that the extra weight can be carried.*60\330\8*

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