The chimps sometimes seemed to show “insight,” Köhler said; they could work through novel problems spontaneously. Most famously, they stacked boxes on top of each other and climbed up on them to reach food hanging out of reach. Köhler weakened the idea that there is a necessary link between language and complex thought. Some evidence pushes this way even in the human case. The Canadian psychologist Merlin Donald’s book Origins of the Modern Mind, published in 1991, made use of two “natural experiments.” First, he looked at evidence about the lives of deaf people in preliterate cultures that
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