In this image provided by Joshua M. Plotnik, elephants participate in a test involving food rewards that are placed on a platform on the ground connected to a rope. To get the food the elephants had to pull the two ends of the rope at the same time to drag the platform under the fence. Elephants quickly learned to co-operate to solve a problem, researchers report in Monday's edition of Proceedings of the National Academy of Sciences. The giant mammals are socially complex, explained lead researcher Plotnik. (AP Photo/Joshua M. Plotnik)

Photo by: Joshua M. Plotnik

In this image provided by Joshua M. Plotnik, elephants participate in a test involving food rewards that are placed on a platform on the ground connected to a rope. To get the food the elephants had to pull the two ends of the rope at the same time to drag the platform under the fence. Elephants quickly learned to co-operate to solve a problem, researchers report in Monday's edition of Proceedings of the National Academy of Sciences. The giant mammals are socially complex, explained lead researcher Plotnik. (AP Photo/Joshua M. Plotnik)