What foot traits and corresponding functions seen in other primates has been lost in our feet, why would we have lost helpful features such as this?

In some cases, our bipedal adaptations have changed areas of our bodies so much that it is difficult (if not impossible) for these areas to perform other functions.  For example, our pelvis provides the areas of muscle attachment that we need, but its unusual shape makes human childbirth more difficult. The foot is another area that reflects the impact of bipedal specialization. What foot traits and corresponding functions seen in other primates has been lost in our feet, why would we have lost helpful features such as this?