Chimps spread out their tools.

Chimpanzees use stones to crack open hard-shelled nuts in Cameroon's Ebo Forest, more than 1,700 kilometers (1,000 miles) east of a river previously thought to have prevented the inland spread of this behavior.

Until now, nut cracking had been reported only in chimp groups living west of the N'Zo-Sassandra River, which cuts vertically through Cote d'Ivoire not far from Africa's west coast. But last September, Bethan J. Morgan and Ekwoge E. Abwe, both of the Zoological Society of San Diego, observed three adult chimps sitting in a tree in the Ebo Forest busily cracking nuts that contain nutrient-rich seeds. Each animal smashed open its snacks with a grape-fruit-size stone, the researchers report in the Aug. 22 Current Biology.

Widely separated chimp populations may have independently invented the nut-cracking technique, Morgan and Abwe suggest. Alternatively, this behavior may have originated in an ancient chimp group and then spread across western Africa, only to be abandoned later by chimps living between the N'Zo-Sassandra River and the Ebo Forest.

Social traditions in various chimp populations may die out over time, possibly explaining why ape culture has never flourished to the extent that human culture has, remarks Richard W. Wrangham of Harvard University.