Primal people who had only simple or no footwear had feet that look like this (thanks to Tim Ferris at The Four Hour Work Week for the first three images in this post):
The toes have interspaces, the ball is wide, the basic shape is almost triangular, and you can draw a straight line through the big toe to the opposite corner of the heel, making this a very stable foundation for posture. Modern people who wear toe-squeezing footwear have feet like this:
Obviously the latter provides a much less stable foundation for movement, and this transmits up the legs and thighs to the torso. Dysfunctional (non-primal) feet form a foundation for ankle, knee, hip, lumbar, and neck dysfunction.
Moreover, the use of elevated heels forces the body to compensate by exaggerating lordosis (lumbar curve) and kyphosis (upper back curve), which again causes lumbar and neck pain and dysfunction:
My father has feet similar to those depicted in the second image above, deformed by wearing shoes too small when a child, so my parents made sure I had “roomy” shoes. Nevertheless, my feet look like this:
Not quite as wide and stable as primal feet, but not as deformed as feet forced to conform to shoes too narrow or small.
To move in the direction of primal feet, I use gel toe spreaders:
After just half an hour of wearing the toe spreaders, my feet look like this:
So I aim to wear them for an hour or more every day when at home. I also wear Vibram Five Fingers KSO Treks all day long at my office:
Which is a little better than the first photo of my feet above, which was taken after some time in regular shoes. So it looks like a consistent use of the toe spreaders and Five Fingers shoes will help me get primal feet.