[Sabertooth]

I could be wrong, but I believe the threshold for "repeatedly" is only a few whacks in one spot, enough to distinguish it from the natural bumping and grinding of stones. A couple of nuts should do it.

I don't know either, but let's assume this is the case.

First, I still believe the earliest stone tools would be used once and disposed. Once you got to the point where a particular stone was used repetedly, that would suggest some way to keep track of it, probably at least a semi-permanent residence.

Such a clan of apes would by definition be isolated to a degree from others... who knows for how long? Toolmaking could have developed for a while before being learned by others of the species.

So I don't think it's a given that we've discovered the earliest stone tools, or even any that are necessarily close to the earliest.

So, any archaeologists lurking out there, start sifting the pebbles!

[Physicist]

So I don't think it's a given that we've discovered the earliest stone tools

Perhaps not, but we've probably discovered the earliest stone tools worth carrying. And if we're postulating that carried tools prompted us to evolve bipedalism, then we'd expect tools worth carrying to be as widespread as walking hominids throughout the fossil record. Since they manifestly aren't, we'd also have to postulate that the carrying of at least stone tools fell out of fashion, for a few thousand millenia, with the descendants of the apes who were bootstrapped (a singularly appropriate term) to bipedalism by the process of carrying them. But why would it cease to be an advantage?