People are indeed top-heavy, and balance, the ability to stand upright and move around without falling over, is not as simple as it feels.
It requires constant tiny adjustment of muscles as the weight shifts on the feet, much as a juggler maneuvers to balance a plate on a stick.
The adjustments become unconscious and are carried out automatically once a child learns to walk.
However, balance relies on processing a constant flow of information about the body’s position, sent to the brain from sensors all over the body.
Signals are then sent back to the body parts to make the needed changes. The coordinator is the cerebellum, at the base of the brain.
One key set of sensors is the eyes.
But even a blindfolded person can stand upright, because nerves in the skin muscles and joints, called proprioreceptors, inform the brain about the body’s position.
There are also important sensors in the inner ear.
In the vestibule, tiny stones or crystals, called otoliths, meaning “ear stones”, hang on stalks called hair cells.
When the head moves, the stones move, stimulating the hair cells, which send signals to the brain.
Other hair cells in the ear’s semicircular canals float in fluid and move when it moves.