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Scientific News  Hypotheses Historical hypotheses SOIL SUGGESTS EARLY HUMANS LIVED IN FORESTS INSTEAD OF GRASSLANDS
SOIL SUGGESTS EARLY HUMANS LIVED
IN FORESTS INSTEAD OF GRASSLANDS
 Carbon
isotope evidence in almost 6-million-year-old soils suggests that the earliest
humans already were evolving in - and likely preferred - humid forests rather
than grasslands, report a team of scientists working in Ethiopia.
The discovery challenges long-held beliefs, beginning with Darwin, that humans
did not evolve into upright beings and thrive until expanding tropical
grasslands forced our chimpanzee-like ancestors out of dwindling forests about 4
million to 8 million years ago.
Hominid fossil sites from the later Pliocene period (2.5 million to 4.2 million
years ago) previously had been found in savanna habitats. Researchers had been
confident that the slightly earlier hominids living in the late Miocene also
would be found in the savanna.
"The expectation was that we would find hominids in savanna grassland sites
that date back to about 8 million years ago. That hasn't happened," said
anthropologist Stanley H. Ambrose of the University
of Illinois. "All older hominids have been found in forested
environments."
The analysis was of fossil soils from paleontological sites in the Middle Awash
region of Ethiopia's rift valley, where the remains of a new subspecies of
Ardipithecus ramidus have been discovered. They date to the late Miocene period
(5.4 million to 5.8 million years ago). Scientists from four institutions report
their findings in a pair of papers that appear in the July 12 issue of the
journal Nature.
 Ambrose
collected fossil soil samples from the layers containing the newly found
hominids. One of the fossils was found by team member Leslea Hlusko, also a UI
professor of anthropology. Ambrose performed geochemical studies on the samples
in his UI laboratory.
The region where the fossils were found is now a hot, dry semi-desert occupied
by nomadic camel herders. At the time the area formed, it was higher in
elevation, cooler, wetter and more forested.
Ambrose's geochemical technique allows for an
environmental reconstruction of soils by examining the carbonate nodules (caliche)
in the samples. The nodules reflect the types of plants that grew in the soils.
Tropical grasses contain more of the heavy isotope of carbon than do trees,
shrubs and leafy plants.
The nodules from these late-Miocene hominid fossil sites contain low levels of
carbon 13, which is consistent with trees and woody plants. They also contain
oxygen isotope ratios that are indicative of a cool, humid climate.
"These hominids were living in the forest, despite the fact that grasslands
were available," Ambrose said.
The new findings, he said, require a fundamental reassessment of models that
invoke a significant role for global climatic change and/or adaptation to
savanna habitats in the origin of hominids.
Ambrose's findings appear in a paper cowritten with seven other researchers: Tim
White, Yohammes Haile-Selassie and Paul R. Renne of the University of California
at Berkeley; Giday WoldeGabriel and Grant Heiken of the Los Alamos National
Laboratory in New Mexico; William K. Hart of Miami University in Oxford, Ohio;
and Berhane Asfaw of the Rift Valley Research Service in Addis Adaba, Ethiopa.
The National Science Foundation and the University of Illinois Research Board
provided funding for Ambrose's research.
Jim Barlow, Life Sciences Editor
(217) 333-5802; b-james3@uiuc.edu
Source of the given news
and the copyrights belong to a University
of Illinois
Publishing date: July 26, 2001
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