What type of surface were human feet originally adapted to

[GRB 080319B]

What type of surface were human feet originally adapted to navigate (plain/savannah, desert, ect.) and have there been any significant physiological changes to the foot throughout human evolution or between humans inhabiting different environments?

Thank you.

 

[Danger]

As far as I know, they were originally more like those of an ape, designed for life in trees. As we began walking upright, the toes shortened and the big one migrated from its opposable position to the front for balance.