I am convinced that early humans were a lot smarter then given credit for. My guess is the same as yours and that they were part of a long chain of steps of learning and development that went back much farther then we have evidence for.
Possibly however homo erectus used the same design for their hand axes for over a million years. This implies the design was hardwired in their brains, in the same way the design of nests are hardwired in bird brains, as opposed to a rationally thought out design.
