In the new study, Cerling says he and colleagues developed "a new way to quantify the openness of tropical landscapes. This is the first method to actually quantify the amount of canopy cover, which is the basis for deciding if something is savanna."
Cerling does not dispute that East African savannas became more expansive within the past 2 million years, or that human ancestors and relatives likely spent time in narrow "gallery forests" along river corridors.
But he says the new method shows grasslands and wooded grasslands in other words, savannas have prevailed for more than 6 million years in the cradle of humanity, with tree cover less than about 40 percent at most sites. By definition, woodland has more than 40 percent tree cover, and a forest has more than 80 percent tree cover.
"In some periods, it was more bushy, and other times it was less bushy," he says. "Hardly anything could have been called a dense forest, but we can show some periods where certain environments were consistently more wooded than others. We find hominins (early humans, pre-humans and chimp and gorilla relatives) in both places. How early hominins partitioned their time between 'more open' and 'more closed' habitats is still an open question."
Cerling says even sparse woody canopy provided hominins with shade, some foods and refuge from predators.
Fossil evidence of hominins humans, their ancestors and early relatives such as chimps and gorillas date back to 4.3 million years and possibly 6 million years, Cerling says. The new method was used to look for and find savanna up to 7.4 million years ago.
"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 says. "This study shows that during the development of bipedalism [about 4 million years ago
|Contact: Lee Siegel|
University of Utah