People who never wear shoes will actually develop pretty thick callouses on their feet over the course of their lifetime. When Shaka kaSenzangakhona created the Zulu Kingdom at the beginning of the 19th Century, one of his innovations was to outlaw sandals so all of his warriors would be able to run cross-country without complaint. There are several recorded instances where British and Boers visited old battlefields years later and saw the Zulu dead had been reduced to just skeletons and the thick skins on the soles of their feet: Everything else had been eaten or weathered away.

Source: My go-to with almost anything on the Zulu is always John Laband's excellent The Rise & Fall of the Zulu Nation. That book is damned-near definitive. Don't get me wrong: I'm a big fan of Ian Knight too, but it is a crying shame Laband's work isn't better known.

The oldest human footprints are the Laetoli tracks which were dated at 3.66 Ma; they are of course unshoed. Functionnal analysis indicates that the gait was functionally similar to that of modern human feet. (source)