Long journey of Indonesian Homo erectus: Arrival and dispersal in Java Island

The presence of Homo erectus in the Archipelago was identified very early when human remains were found in various ancient deposits on Java Island. The widespread distribution in the global Old World indicates their long migration route since they left Africa around 1.8 million years ago, spreading to Europe, East, and Southeast Asia, until finally reaching Java Island as the easternmost end of their migration route. Sea level regression during the Ice Age, which formed a land bridge across the Sunda Shelf, allowed migration during the Pleistocene from mainland Southeast Asia to islands Southeast Asia. Interpreted to have reached Java in the early Lower Pleistocene, their oldest fossils were found at Bumiayu, Sangiran, and Mojokerto. Their dispersal occurred for more than 1.5 million years on Java, with the discovery of younger Homo erectus sites in chronology. Discovery of the Middle Pleistocene Period were mainly deposited in volcanic layers of the Kabuh Formation in Sangiran, as well as Trinil, Kedungbrubus, Semedo, Rancah, and Patiayam. While related to younger chronologies, their fossil remains were found in the alluvial deposits of the Bengawan Solo at the sites of Ngandong, Sambungacan, and Ngawi. This assemblage of Javanese Homo erectus fossils consists of various anatomical components, mostly cranial and its fragments, complemented by maxilla-mandibular components, isolated teeth, and post-cranial fragments. Morphological, metric, geologic-stratigraphic, and radiometric dating analyses applied to these Homo erectus fossils indicate three evolutive stages among Javanese Homo erectus during the Pleistocene, namely – from the oldest to the youngest ones – archaic Homo erectus, typical Homo erectus, and progressive Homo erectus. The variability of earlier taxonomic names, such as Pithecanthropus (erectus, robustus, dubius, modjokertensis, soloensis) and Meganthropus paleojavanicus, are merely historical names given by researchers at the time and do not indicate genus or species differences. Within the evolutionary scope of Homo erectus in Java, there is only one genus (Homo) and one species (erectus).