Repeated innovation in great apes

Innovation has been defined as a solution to a novel problem or a novel solution to an old problem. The second part of this definition requires the inhibition of previously learnt solution strategies before a novel solution can be found. Therefore, inventing novel solutions for an old problem is considered to be particularly difficult. We investigated the ability of great apes to produce multiple new solutions to a task after each of those solutions became obsolete. We presented all four nonhuman great ape species with a task consisting of extracting a food reward from a puzzle box. Initially, the task could be solved in three different ways that varied in difficulty. After subjects discovered the first solution, we allowed them to use it for some trials and then it became obsolete. If the apes could overcome their initial response and find the next solution, we again allowed them to use it for some time and once again it became obsolete. The final step consisted of finding the third solution to secure the food reward. We found that all species except orang-utans, Pongo abelii, were able to solve all versions of the problem. Furthermore, they overcame the obsolete techniques quickly and efficiently, indicating high degrees of behavioural flexibility and inhibitory control. In contrast to previous research on social learning, our results suggest that great apes are not conservative and adjust their behaviour flexibly when the physical constraints of a task change.