Is nut cracking in wild chimpanzees a cultural behaviour?

Nut cracking behaviour, once thought to be typical for most West African chimpanzees, is in reality restricted to a very small area within the evergreen forest perimeter. In Côte d'Ivoire, the N'Zo-Sassandra river is the eastern limit of its distribution. Neither the chimpanzee density, the density of nut-producing tree, anvils and hammers, nor the type of forest can explain this clear-cut limit. From two cases of chimpanzee populations less than 50 km apart on either side of the river we can conclude that this limit is most probably cultural. This result completes the image of cultural behaviour in wild chimpanzees having irregular and unpredictable distribution patterns similar to those of human culture.