Ancestral humano mais antigo do que antes 'imaginado'

sexta-feira, julho 01, 2011

Human Ancestor Older Than Previously Thought; Finding Offers New Insights Into Evolution

ScienceDaily (June 30, 2011) — Modern humans never co-existed with Homo erectus -- a finding counter to previous hypotheses of human evolution -- new excavations in Indonesia and dating analyses show. The research, reported in the journal PLoS ONE, offers new insights into the nature of human evolution, suggesting a different role for Homo erectus than had been previously thought.

Generalized composite sedimentary geology of the Ngandong and Jigar “20 meter terrace" denoting stratigraphic positions of Homo erectus fossil material and dated pumices. (Credit: Etty Indriati, Carl C. Swisher, Christopher Lepre, Rhonda L. Quinn, Rusyad A. Suriyanto, Agus T. Hascaryo, Rainer Grün, Craig S. Feibel, Briana L. Pobiner, Maxime Aubert, Wendy Lees, Susan C. Antón. The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia. PLoS ONE, 2011; 6 (6): e21562 DOI: 10.1371/journal.pone.0021562)

The work was conducted by the Solo River Terrace (SoRT) Project, an international group of scientists directed by anthropologists Etty Indriati of Gadjah Mada University in Indonesia and Susan Antón of New York University.

Homo erectus is widely considered a direct human ancestor -- it resembles modern humans in many respects, except for its smaller brain and differently shaped skull -- and was the first of our ancestors to migrate out of Africa, approximately 1.8 million years ago. Homo erectus went extinct in Africa and much of Asia by about 500,000 years ago, but appeared to have survived in Indonesia until about 35,000 to 50,000 years ago at the site of Ngandong on the Solo River. These late members of Homo erectus would have shared the environment with early members of our own species, Homo sapiens, who arrived in Indonesia by about 40,000 years ago.

The existence of the two species simultaneously has important implications for models about the origins of modern humans. One of the models, the Out of Africa or replacement model, predicts such overlap. However, another, the multiregional model, which posits that modern humans originated as a result of genetic contributions from hominin populations all around the Old World (Africa, Asia, Europe), does not. The late survival of Homo erectus in Indonesia has been used as one line of support for the Out of Africa model.

However, findings by the SoRT Project show that Homo erectus' time in the region ended before modern humans arrived there. The analyses suggest that Homo erectus was gone by at least 143,000 years ago -- and likely by more than 550,000 years ago. This means the demise of Homo erectus occurred long before the arrival of Homo sapiens.

"Thus, Homo erectus probably did not share habitats with modern humans," said Indriati.


The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia

Etty Indriati1, Carl C. Swisher III2*, Christopher Lepre2,3,Rhonda L. Quinn2,4, Rusyad A. Suriyanto1, Agus T. Hascaryo1, Rainer Grün5, Craig S. Feibel2, Briana L. Pobiner6, Maxime Aubert5, Wendy Lees5, Susan C. Antón7*

1 Laboratory of Bio and Paleoanthropology, Faculty of Medicine, Gadjah Mada University, Yogyakarta, Indonesia, 2 Department of Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, United States of America, 3 Lamont Doherty Earth Observatory Palisades, Columbia University, New York, New York, United States of America, 4 Department of Anthropology, Loyola University of Chicago, Chicago, Illinois, United States of America, 5 Research School of Earth Sciences, The Australian National University, Canberra, Australia, 6 Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, D. C., United States of America, 7 Center for the Study of Human Origins, Department of Anthropology, New York University, New York, New York, United States of America


Homo erectus was the first human lineage to disperse widely throughout the Old World, the only hominin in Asia through much of the Pleistocene, and was likely ancestral to H. sapiens. The demise of this taxon remains obscure because of uncertainties regarding the geological age of its youngest populations. In 1996, some of us co-published electron spin resonance (ESR) and uranium series (U-series) results indicating an age as young as 35–50 ka for the late H. erectussites of Ngandong and Sambungmacan and the faunal site of Jigar (Indonesia). If correct, these ages favor an African origin for recent humans who would overlap with H. erectus in time and space. Here, we report 40Ar/39Ar incremental heating analyses and new ESR/U-series age estimates from the “20 m terrace" at Ngandong and Jigar. Both data sets are internally consistent and provide no evidence for reworking, yet they are inconsistent with one another. The 40Ar/39Ar analyses give an average age of 546±12 ka (sd±5 se) for both sites, the first reliable radiometric indications of a middle Pleistocene component for the terrace. Given the technical accuracy and consistency of the analyses, the argon ages represent either the actual age or the maximum age for the terrace and are significantly older than previous estimates. Most of the ESR/U-series results are older as well, but the oldest that meets all modeling criteria is 143 ka+20/−17. Most samples indicated leaching of uranium and likely represent either the actual or the minimum age of the terrace. Given known sources of error, the U-series results could be consistent with a middle Pleistocene age. However, the ESR and 40Ar/39Ar ages preclude one another. Regardless, the age of the sites and hominins is at least bracketed between these estimates and is older than currently accepted.

Citation: Indriati E, Swisher CC III, Lepre C, Quinn RL, Suriyanto RA, et al. (2011) The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia. PLoS ONE 6(6): e21562. doi:10.1371/journal.pone.0021562

Editor: Fred H. Smith, Illinois State University, United States of America

Received: January 17, 2011; Accepted: June 3, 2011; Published: June 29, 2011

Copyright: © 2011 Indriati et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The project was funded by the U.S. NSF BCS 0317292 to SCA, an AAAS WISC program grant to EI and SCA, and a UGM sabbatical grant to EI. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.