Why is the human spine considered a bad design from an engineering perspective?

When engineers design a structure they usually plan on a lifetime of 50 years with minor maintenance. Our spine shape, like everything in biology, was not designed on purpose but it came about through random mutation and natural selection. Natural selection works a a greedy algorithm, this is, biology cannot take a leap back to a complete redesign when one evolutionary path was chosen.

The main problem is that the spine has to accommodate bipedalism instabilities and that the spine we have evolved mainly when we were not bipedals. Humans started to walk on two legs a short while ago in evolutionary timescales, therefore the spine is forced to support loads for which was never optimized for, working as a curved cantilever beam, supporting a big heavy head at the end of the cantilever.

Besides, serious problems of the human spine are caused by the materials from which it is built. Those materials have very little resistance to fatigue damage caused by repetitive loads. Sometimes the head which sits on top of the spine leads the individual to mechanical overloading. Repetitive loading leads to endplate failure which leads to disc degeneration. What is more, When subject to low oxygen caused by cigarette abuse, the discs lose their ability for self reparation and start to degenerate. The spine has a pretty small section to distribute all that weight from the top of the body to the hip. The rate of degeneration due to dynamic loads is dependent on those repetitive loads and genetic factors that govern the dynamic characteristics of the connective tissue from which discs are made and the ability to repair microcracks.

In conclusion, our body spine is far from perfect. Mind that it is not structurally very sound to support extreme weights and cyclic loads. Take care of it.