The artifacts found at Longtan, southwest China, were as old as 60,000 years. New technologies today often involve electronic devices that are smaller and smarter than before. During the Middle Paleolithic , when Neanderthals were modern humans' neighbors, new technologies meant something quite different: new kinds of stone tools that were smaller but could be used for many tasks and lasted for a long time. Archaeologists like me are interested in the Middle Paleolithic — a period spanning 250,000 to 30,000 years ago — because it includes the first appearance of our species, our arrival into many parts of the…