The GPTS dating of the plateau’s layers shows that the artifacts were discarded by human inhabitants over a 0.85-million-year period, during which time the area’s climate switched back and forth from warm and wet to cold and dry more than two dozen times. Five times more tools were found in the warm-weather soil layers than in the glacial silty layers, advancing an intuitive theory that the Loess hominin population thrived in tropical phases and faced increased hardship during ice ages.
“[I]t appears that these early populations were limited by climatic extremes, and only were able to expand north during warmer intervals,” Kappelman added. “What they were doing with the tools remains to be demonstrated, but the circumstantial evidence suggests that they might have used them to process food items.”
Given the lack of fossils, it is impossible to say what species of hominin made these tools, and given the many gaps in our understanding of the human evolutionary tree, it would be difficult to assign certainty even if Zhu’s excavation had uncovered human bones. Currently, the oldest confirmed specimen of an individual belonging to the modern human genus Homo is a 2.8 Ma jawbone found in Ethiopia, suggesting the lineage may have arisen around that time. According to Kappelman, because no fossils of earlier hominins, like Australopithecus, have been found outside of Africa, many in the field believe that some unidentified species of Homo was the first to leave. The Dmanisi skulls support this, as they have many morphological similarities to the earliest Homo species in Africa.
Until the next exciting discovery, the mysteries of our origins abound.