SALT LAKE CITY, Aug. 3 (UPI) -- A U.S. study questions the theory that early humans evolved in closed woodland in Africa and then moved to open savannah as they become bipedal.

Researchers at the University of Utah say an analysis of fossil soils in regions associated with early hominins in eastern Africa 6 million years ago suggests our early ancestors evolved in a savannah-like environment with less than 40 per cent tree cover, rather than in more closed woodland.

Fossil soils can yield information about the vegetation that once grew in the regions and can provide clues to the type of ecosystem that existed in different time periods, a university release said Wednesday.

"We've been able to quantify how much shade was available in the geological past," said geochemist Thure Cerling, one author of a study appearing in 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," he said.

"Currently, many scientists think that before 2 million years ago, things were forested [in East Africa] and savanna conditions have been present only for the past 2 million years," Cerling said. "This study shows that during the development of bipedalism [about 4 million years ago] open conditions were present, and even predominant, he said.