ScienceDaily (Oct. 21, 2009) — In an article published in the open-access, peer-reviewed journal PLoS ONE on October 21, 2009, Dr Thomas Plummer of Queens College at the City University of New York, Dr Richard Potts of the Smithsonian Institution National Museum of Natural History and colleagues report the oldest archeological evidence of early human activities in a grassland environment, dating to 2 million years ago. The article highlights new research and its implications concerning the environments in which human ancestors evolved.
Fossils, including an Antidorcas recki hemimandible and innominate, and an equid tooth, associated with flakes in Excavation 1. Scale in inches. (Credit: Thomas Plummer)
Scientists as far back as Charles Darwin have thought that adaptation to grassland environments profoundly influenced the course of human evolution. This idea has remained well-entrenched, even with recent recognition that hominin origins took place in a woodland environment and that the adaptive landscape in Africa fluctuated dramatically in response to short-term climatic shifts.
During the critical time period between 3 and 1.5 million years ago, the origin of lithic technology and archeological sites, the evolution of Homo and Paranthropus, selection for endurance running, and novel thermoregulatory adaptations to hot, dry environments in H. erectus have all been linked to increasingly open environments in Africa.
However, ecosystems in which grassland prevails have not been documented in the geological record of Pliocene hominin evolution, so it has been unclear whether open habitats were even available to hominins, and, if so, whether hominins utilized them. In their new study, Plummer and colleagues provide the first documentation of both at the 2-million-year-old Oldowan archeological site of Kanjera South, Kenya, which has yielded both Oldowan artifacts and well-preserved faunal remains, allowing researchers to reconstruct past ecosystems.
The researchers report chemical analyses of ancient soils and mammalian teeth, as well as other faunal data, from the ~2.0-million-year-old archeological sites at Kanjera South, located in western Kenya. The principal collaborating institutions of the Kanjera project are QueensCollege of the City University of New York, the Smithsonian Institution's Human Origins Program, and the NationalMuseums of Kenya. The findings demonstrate that the recently excavated archeological sites that preserve Oldowan tools, the oldest-known type of stone technology, were located in a grassland-dominated ecosystem during the crucial time period.
The study documents what was previously speculated based on indirect evidence -- that grassland-dominated ecosystems did, in fact, exist during the Plio-Pleistocene (ca. 2.5-1.5 million years ago) and that early human tool-makers were active in open settings. Other recent research shows that the Kanjera hominins obtained meat and bone marrow from a variety of animals and that they carried stone raw materials over surprisingly long distances in this grassland setting. A comparison with other Oldowan sites shows that by 2.0 million years ago, hominins, almost certainly of the genus Homo, lived in a wide range of habitats in East Africa, from open grassland to woodland and dry forest.
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Oldest Evidence of Toolmaking Hominins in a Grassland-Dominated Ecosystem
Thomas W. Plummer1*, Peter W. Ditchfield2, Laura C. Bishop3, John D. Kingston4, Joseph V. Ferraro5, David R. Braun6, Fritz Hertel7, Richard Potts8,9
1 Department of Anthropology, Queens College and NYCEP, Flushing, New York, United States of America, 2 Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford, United Kingdom, 3 Research Centre in Evolutionary Anthropology and Palaeoecology, School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, United Kingdom, 4 Department of Anthropology, Emory University, Atlanta, Georgia, United States of America, 5 Department of Anthropology, Baylor University, Waco, Texas, United States of America, 6 Department of Archaeology, University of Cape Town, Rondebsoch, South Africa, 7 Department of Biology, California State University, Northridge, Northridge, California, United States of America, 8 Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, D. C., United States of America, 9 Paleontology Section, Earth Sciences Department, National Museums of Kenya, Nairobi, Kenya
Abstract Top
Background
Major biological and cultural innovations in late Pliocene hominin evolution are frequently linked to the spread or fluctuating presence of C4 grass in African ecosystems. Whereas the deep sea record of global climatic change provides indirect evidence for an increase in C4 vegetation with a shift towards a cooler, drier and more variable global climatic regime beginning approximately 3 million years ago (Ma), evidence for grassland-dominated ecosystems in continental Africa and hominin activities within such ecosystems have been lacking.
Methodology/Principal Findings
We report stable isotopic analyses of pedogenic carbonates and ungulate enamel, as well as faunal data from ~2.0 Ma archeological occurrences at Kanjera South, Kenya. These document repeated hominin activities within a grassland-dominated ecosystem.
Conclusions/Significance
These data demonstrate what hitherto had been speculated based on indirect evidence: that grassland-dominated ecosystems did in fact exist during the Plio-Pleistocene, and that early Homo was active in open settings. Comparison with other Oldowan occurrences indicates that by 2.0 Ma hominins, almost certainly of the genus Homo, used a broad spectrum of habitats in East Africa, from open grassland to riparian forest. This strongly contrasts with the habitat usage of Australopithecus, and may signal an important shift in hominin landscape usage.
Citation: Plummer TW, Ditchfield PW, Bishop LC, Kingston JD, Ferraro JV, et al. (2009) Oldest Evidence of Toolmaking Hominins in a Grassland-Dominated Ecosystem. PLoS ONE 4(9): e7199. doi:10.1371/journal.pone.0007199
Editor: David S. Strait, University at Albany (SUNY), United States of America
Received: June 8, 2009; Accepted: August 16, 2009; Published: October 21, 2009
Copyright: © 2009 Plummer 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: Funding from the L. S. B. Leakey Foundation, the Leverhulme Trust, the National Geographic Society, the National Science Foundation, the Professional Staff Congress-City University of New York Research Award Program, and the Wenner-Gren Foundation for Kanjera field and laboratory research is gratefully acknowledged. Logistical support was provided by the Human Origins Program of the Smithsonian Institution. 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.
* E-mail: thomas.plummer@qc.cuny.edu
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