in most mammals, the spine is usually horizontal in monkeys swinging from branch to branch, the spine has evolved to operate vertically under tension in humans (and other animals that walk on two legs), the spine is in compression when vertical did humans evolve from swinging monkeys? would it be better for our spines if we spent some time swinging around, with our spines in tension? or if we slept in a hanging position (possibly upside-down)? or on a horizontal rotating bed (with the ears at the centre)? what would be the effects be?