June 2011, Daily News

Human Ancestor in Indonesia Died Out Earlier Than Once Thought

Thu, Jun 30, 2011

Homo erectus, an ancient human ancestor that lived 1.8 million - 35,000 years ago, is said by theorists of human evolution to have lived alongside Homo sapiens (modern humans) in Indonesia, surviving most other Homo erectus populations that became extinct in Africa and most of Eurasia by 500,000 B.P.  Perhaps not so, according to an international team of researchers, after conducting archaeological investigations and a new dating study at sites on the Solo river in Indonesia.

The work, in progress since 2004, was conducted by a team of scientists (the SoRT, or Solo River Terrace Project) under the direction of anthropologists Etty Indriati of Gadja Mada University, Indonesia, and Susan Antón of New York University. It involved geological surveys, site trenching, archaeological excavations, and analyses of animal remains related to two sites, Ndangong and Jigar, composed of terraces formed by sediment deposits along the Solo river. Historically, the terraces have been a rich source of human and animal fossils since the 1930's. In 1996, scientists dated Homo erectus fossils found at these sites to about 35,000 - 50,000 years ago, based on the dating of associated animal fossil teeth. This dating placed the early human finds contemporaneous with other Homo sapiens finds in Indonesia, suggesting that late-surviving Homo erectus individuals and Homo sapiens (who arrived in Indonesia about 40,000 years ago) shared the same environment at the same time. The SoRT team expedition, however, arrived at different results. Their findings indicate that Homo erectus was extinct in the area by at least 143,000 years ago, and more probably by at least 550,000 years ago, long before the arrival of Homo sapiens.

This is significant because scholarly critics of the earlier (1996) expedition finds have suggested that the sites may have contained a mixture of the fossil remains of younger animals and older homin (early human) fossils, which cast doubt in some minds about the validity of the dates assigned to the homin remains. Mixing often occurs through events, such as water activity or geologic events, that may intermingle older and newer fossils and artifacts into the same stratigraphic relationship. The SoRT Project, in part, was designed to test for this possibility, along with application of additional dating tests and analysis to enhance the data base that has been used for analysis of the sites.

Evidence found from the newer excavations of the sediments indicated that the sediments were actually deposited over a very short time period, and that intermixing of sediments from different time periods, and thus by extension the artifacts and fossils contained within them, did not occur. "Whatever the geological age of the site is, the hominins, animals and sediments at Ngandong and Jigar are all the same age," maintains project co-leader Antón. Moreover, analysis of the animal remains suggested the same conclusion. According to project team expert Briana Pobiner, a paleoanthropologist with the Smithsonian Museum of Natural History in Washington, D.C., "the postmortem damage to the animal remains is consistent and suggests very little movement of the remains by water. This means that it is unlikely that very old remains were mixed into younger ones."  To this extent, the SoRT Project finds and interpretation support that of the earlier 1996 expedition. 

Regarding actual dates, however, the picture changes. The project team applied three different dating techniques to the finds at the sites. All three depended upon rates of radioactive decay (similar to radio-carbon dating, often used to date organically based materials found within the context of key artifactual or fossil finds). The first two, U-series and ESR (Electron Spin Resonance), applied to fossil teeth as in the earlier 1996 tests, yielded dates approaching 143,000 years. The third methodology, argon-argon, was applied to pumice material, a light, porous volcanic rock found within the sediments. The results of this application yielded relatively precise dates around 550,000 years. Project scientists posit different plausible theories or possibilities that might account for the enormous gap between the dates obtained from the first two techniques and that of the argon-argon, but all agree on one thing -- they provide a minimum and a maximum date for a time range that clearly and significantly predates those suggested by the earlier study. According to SoRT, Homo erectus could not have inhabited Indonesia, or at least these locations in Indonesia, any later than about 143,000 years B.P. "Thus," says Indriati, "Homo erectus probably did not share habitats with modern humans."

________________________________________________________________________________________________________________________

 Sangiran 17, a Homo erectus fossil specimen found in Indonesia. Courtesy Gerbil, Wikimedia Commons.

_______________________________________________________________________________________________________________________

The results of the SoRT Project work has implications for current theories about the origins of modern humans. The "Out of Africa" model, perhaps the most widely held theory among evolutionists today, suggests that geographic and time-period overlapping between disparate early human species, and more particularly that of Homo erectus and Homo sapiens, would be predictable. It posits that archaic Homo sapiens (an earlier version of modern humans) evolved to anatomically modern humans solely in Africa between 200,000 and 150,000 years ago, and that members of anatomically modern humans left Africa by between 125,000 and 60,000 years ago, replacing earlier human populations such as Neanderthals and Homo erectus over time. Geographic and time period overlapping would be a natural occurrence under this scenario.  The "Muliti-regional Hypothesis", on the other hand, does not predict such an occurrence. It holds that humans first arose near the beginning of the Pleistocene two million years ago and that evolution occurred within a single species, which included a variety of forms such as Homo erectus and Neanderthals. This species evolved into the currently diverse anatomically modern human populations known today by a combination of adaptations within various regions of the world and gene flow between those regions.

The research was sponsored by the National Science Foundation and is reported in the journal, PLoS One. Co-authors of the study include Rusyad Suriyanto and Agus Hascaryo of Gadjah Mada University and Wendy Lees and Maxime Aubert of the Australian National University.  

Cove Photo, Top: Homo erectus KNM-ER 3733. Courtesy Gerbil, Wikimedia Commons.