The Significance of Base Camps Richard Klein makes this interesting comment: If stone artifacts existed before 2.6 my ago, they may prove difficult to find since, unlike later artifact makers, the earliest ones may have been too mobile to accumulate archeologically visible clusters of debris. The archaeological record would be largely invisible if people had not developed the uniquely human habit of returning to the same site for at least a few days (or nights). (R G Klein, The Human Career), p228 Even if fire was not yet in use, bipeds living in open country might well have returned to a base camp at night for reasons of safety - a safer location in trees or a cave would make the undetected approach by nocturnal predators more difficult; even in the open there would be safety in numbers, the youngest and most vulnerable sleeping in the centre of a large group. Of course a fire would also provide an additional element of safety. Once fire was in use, it could be tended all day by a member of the group and food would be cooked for all before bedtime. Australopithecines, good climbers living initially in more wooded country, would have nested in a handy tree each night, as chimpanzees still do; they did not use fire and so had no reason to come to a base camp. So if Klein is right, they could have been making stone implements without leaving any noticeable evidence of it.