There is an appealing framework in Boyd and Richerson’s book on social learning and adaptation  on how the environment’s variability generates the pressure to adapt.
This came to mind watching the latest episode of Attenborough’s Life series on Hunters and Hunted. There is a beautiful account towards the end of the program about an orca mother using her invention to hunt seals in a new way -- she is the only one doing it, but her calf is probably learning while being with her.
This could be the perfect illustration to the Boyd-Richerson model, re the evolutionary origin of the ability to learn as adults from each other, and thus the rise of complex culture. If there are a lot of new challanges/opportunities (perhaps as variation in the environment increases), individuals will come up with independent innovations. Then those young that are able to pick the innovations up, will have an adaptive benefit. If there are a lot of these opportunities around, and they keep emerging, then there will be a lot of individual innovations, and a pressure for the young to (a) have the ability to learn, and (b) perhaps to push this ability out to further and further age. This would then lead to the evolution for learning from each other as adults, and the possibility of the fast changing (perhaps, evolving) culture.
 Boyd, R., and P.J. Richerson, (2005), The Origin and Evolution of CulturesOUP. (Here is a review with a good summary of the book.)