from polyscience.org, found at arstechnica

In the case of this study, two dominant female chimpanzees were taught two different methods of getting food out of an apparatus, poking versus lifting. Then these chimps were sent back to their respective clans, where they taught others how to get the food out of the apparatus. But a funny thing happened along the way. Some chimps from the lifting group discovered that poking was more effective than lifting. But instead of continuing to poke, they conformed to the method that the others in their group used.