Better to be a quadruped than a human?
Humans descended from four-legged animals but in most ways are more advanced. Few lions or monkeys are good chess players. But, when contrasted to humans, lions and monkeys also have spines that are far less likely to become painful. In animals that walk on all fours, the weight of the body is distributed evenly over the four legs. Most of the time the spine is held in a more or less horizontal position. The forces that compress the human spine simply do not exist.
In human beings, however, the spine is held in a more-or-less vertical position
