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Feature Article

Ecosystem variability and early human habitats in eastern Africa

Clayton R. Magill, Gail M. Ashley, and Katherine H. Freeman
PNAS first published December 24, 2012 https://doi.org/10.1073/pnas.1206276110
Clayton R. Magill
aDepartment of Geosciences, Pennsylvania State University, University Park, PA 16802; and
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Gail M. Ashley
bDepartment of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854
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Katherine H. Freeman
aDepartment of Geosciences, Pennsylvania State University, University Park, PA 16802; and
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  • For correspondence: khf4@psu.edu
  1. Edited by John M. Hayes, Woods Hole Oceanographic Institution, Berkeley, CA, and approved November 12, 2012 (received for review April 25, 2012)

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Abstract

The role of savannas during the course of early human evolution has been debated for nearly a century, in part because of difficulties in characterizing local ecosystems from fossil and sediment records. Here, we present high-resolution lipid biomarker and isotopic signatures for organic matter preserved in lake sediments at Olduvai Gorge during a key juncture in human evolution about 2.0 Ma—the emergence and dispersal of Homo erectus (sensu lato). Using published data for modern plants and soils, we construct a framework for ecological interpretations of stable carbon-isotope compositions (expressed as δ13C values) of lipid biomarkers from ancient plants. Within this framework, δ13C values for sedimentary leaf lipids and total organic carbon from Olduvai Gorge indicate recurrent ecosystem variations, where open C4 grasslands abruptly transitioned to closed C3 forests within several hundreds to thousands of years. Carbon-isotopic signatures correlate most strongly with Earth’s orbital geometry (precession), and tropical sea-surface temperatures are significant secondary predictors in partial regression analyses. The scale and pace of repeated ecosystem variations at Olduvai Gorge contrast with long-held views of directional or stepwise aridification and grassland expansion in eastern Africa during the early Pleistocene and provide a local perspective on environmental hypotheses of human evolution.

  • climate
  • plant waxes
  • hominins
  • paleovegetation
  • paleoclimate

Footnotes

  • ↵1To whom correspondence should be addressed. E-mail: khf4{at}psu.edu.
  • This Feature Article is part of a series identified by the Editorial Board as reporting findings of exceptional significance.

  • Author contributions: C.R.M., G.M.A., and K.H.F. designed research; C.R.M. and G.M.A. performed research; C.R.M., G.M.A., and K.H.F. analyzed data; and C.R.M., G.M.A., and K.H.F. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1206276110/-/DCSupplemental.

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Ecosystem variability and early human habitats
Clayton R. Magill, Gail M. Ashley, Katherine H. Freeman
Proceedings of the National Academy of Sciences Dec 2012, 201206276; DOI: 10.1073/pnas.1206276110

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Ecosystem variability and early human habitats
Clayton R. Magill, Gail M. Ashley, Katherine H. Freeman
Proceedings of the National Academy of Sciences Dec 2012, 201206276; DOI: 10.1073/pnas.1206276110
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