Study suggests ancient hominins used unmodified volcanic rock spheres as tools / Prehistoric bone tool cache suggests advanced reasoning in early hominins / Ancient hominins had humanlike hands, indicating earlier tool use, study reveals / Geologists reconstruct ecosystems of northern Africa where the first hominins arrived / Fossil hotspots in Africa obscure a more complete picture of human evolution, study says / Migration of hominins out of Africa may have been driven by the first major glaciation of the Pleistocene / Hominins may have left Africa 700,000 years earlier than we thought