Wolfgang Köhler (1887–1967) conducted a famous series of studies on chimpanzees’ methods of problem solving. He placed a bunch of bananas just out of the animals’ reach and then watched how they figured out how to get to the bananas. At first frustrated, the chimps eventually reached an insight about how to use available objects as I tools. This insight often came suddenly in a sort of A-Ha! moment. In one case, a chimpanzee put two sticks together to create a tool long enough to reach the bananas. Another chimp stacked three boxes on top of each other to reach the fruit hanging from the ceiling. Besides showing us the remarkable ingenuity of these animals, this work supported the Gestalt notion that the mind actively creates complete solutions to problems. This is in contrast to the behaviorist assumption that problem solving can only proceed piecemeal by trial and error.