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ThePuzzling Puzzles of H a r r y a r l o w n dE d w a rD e c i H a d

- r -- -o scientists conducted I n the middle of the last century two young --_--_ ,' a I experiments that should have changed the wodd-but did not. Hury F. Harlow w,rs a professor of psychology at the University of Wisconsin who, in the L940s, establishedone of the world's first laboratoriesfor studying primate behavior.One day inL949,Harlow and two colleagues gathered eight rhesus monkeys for a rwo-week experiment on learning. The researchers devised a simple mechanicalpuzzle like the one pictured on the next page. Solving it required three steps: pull out the vertical pin, undo the hook, and lift the hinged cover.Pretty easyfor you and me, far more challenging for a thirteen-pound lab monkey.

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Harlout\ pzzzlc in tbe starting (left) and soloed (rigbt) positions,

The experimenters placed the puzzles in the monkeys' cages to observe how they ssa6lsd-2nd to prepare them for tests of their problem-solving prowess at the end of the two weeks. But almost immediately, something strange happened.Unbidden by any outside urging and unprompted by the experimenrers, the monkeys began playingwith the puzzles with focus, determination, and what looked like enjoyment. And in short order, they began figuring out how the contraptions worked. By the time Harlow tested the monkeys on days 13 and L4 of the experiment, the primates had become quite adept. They solved the puzzles frequently and quickly; two-thirds of the time they crackedthe code in lessthan sixty seconds. Now, this was a bit odd. Nobody had taught the monkeys how to remove the pin, slide the hook, and open the cover. Nobody had rewarded them with food, affection, or even quiet applause when they succeeded. And that ran counrer to the acceptednotions of how primates-including the bigger-brained, less hairy primates known as human beings-behaved. scientists then knew that two main drives powered behavior. The