George may not have been so curious after all, as Yale researchers have shown that humans may be the only primates that learn for learning’s sake.

The study tested whether capuchin monkeys would engage in causal reasoning in the absence or presence of a reward. When presented with a mysterious machine, the monkeys only attempted to reason its workings in the presence of a reward. In contrast, previous research has demonstrated that young children are often curious regardless other benefit. According to Laurie Santos, a Yale psychology professor and the paper’s senior author, the findings suggest that other primates have the ability to reason causally, but that only humans give causal reasoning intrinsic value.

“These results suggest that the gap between human and nonhuman animal causal cognition is in part a gap of motivation, and not just a gap in specific cognitive abilities,” said Brian Edwards, a graduate student at Northwestern University and the paper’s lead author. “People are often interested in learning for learning’s sake. In contrast, monkeys only spontaneously tried to learn which objects would activate the machine when there was the prospect of receiving an immediate food reward.”

The research team adapted a test previously used on young children called the “blicket detector.” Placing certain toys on the detector — a small Styrofoam box — would cause the detector to emit a visual and auditory cue, as well as dispense a food reward during certain trials. Over several varying experiments, researchers operated the blicket detector in front of the monkeys to assess their ability to deduce and test which toys would trigger the device. Though the monkeys sought out combinations of toys to activate the device when a food reward was present, they did not perform a similar investigation when the food dispenser was detached from the machine.

Because the experimental design with monkeys was nearly identical to that previously employed to test humans, Edwards said the results highlight cognitive differences between young humans and adult primates. The willingness to explore without immediate reward, he said, may be one reason why humans are able to accumulate knowledge of their surroundings so quickly.

David Rand, a Yale psychology professor unaffiliated with the research, praised the study for using tools from developmental psychology for studying nonhuman primates.

“I find the results in this paper to be particularly interesting,” Rand said. “In this context, the capuchins may not be less smart, but may instead just care less.”

Very little is known about curiosity in nonhuman primates, Santos said. While it is unknown whether other primates would also fail to investigate similar causal relationships, Santos said Capuchin monkeys seem to be the best place to look for such behavior. Their curious nature and predisposition to use tools makes them likely to explore causal relationships.

Edwards said he hopes to look into more monkey-friendly experimental setups for future investigation into primate curiosity. While the monkeys were not incredibly interested in the blicket detector, he said further research using a different experimental design might be helpful to confirm the results.

“It’s possible that monkeys would be more curious about other types of causal systems, especially those that are more relevant to monkeys in their daily lives,” Edwards said.

Though five monkeys began the experiment, one dropped out in the middle of the study due to pregnancy.