SALT LAKE CITY, Aug. 3, 2011 University of Utah scientists used chemical isotopes in ancient soil to measure prehistoric tree cover in effect, shade and found that grassy, tree-dotted savannas prevailed at most East African sites where human ancestors and their ape relatives evolved during the past 6 million years.
"We've been able to quantify how much shade was available in the geological past," says geochemist Thure Cerling, senior author of a study of the new method in the Thursday, Aug. 4, 2011 issue of the journal Nature. "And it shows there have been open habitats for all of the last 6 million years in the environments in eastern Africa where some of the most significant early human fossils were found."
"Wherever we find human ancestors, we find evidence for open habitats similar to savannas much more open and savanna-like than forested," adds Cerling, a University of Utah distinguished professor of geology and geophysics, and biology.
Fossils of early humans and their ancestors and extinct relatives have been found in both wooded and open environments in East Africa. Even 4.3-million-year-old Ardipithecus which lived in the woods, according to its discoverers had a small component of tropical grasses in its diet, Cerling says.
"The fact it had some means it was going into the savanna, unless it was eating takeout food," he says.
Scientists have spent a century debating the significance of savanna landscape in human evolution, including the development of upright walking, increased brain size and tool use.
Part of the problem has been a fuzzy definition of "savanna," which has been used to describe "virtually everything between completely open grasslands and anything except a dense forest," Cerling says. He adds the most common definition is a fairly open, grassy environment with a lot of scattered trees a grassland or wooded grassland.
Open Landscapes throughout the
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University of Utah