Humboldt’s squirrel monkeys are tricked by French Drop’s sleight of hand
Elias Garcia Peregrin/University of Cambridge
Monkeys with hands like ours fall for the magic of magic tricks, while monkeys without the opposite thumb are not fooled.
Elias Garcia-Peregrine of the National University of Singapore said these differences show how how primates expect others to behave depends on their own anatomy and abilities. said that His research uses magic to reveal aspects of animals’ mental abilities, including how their perceptual systems can be tricked.
Garcia-Pelegrin, a trained magician with 12 years of experience, works with three species of New World monkeys, the Humboldt Squirrel monkeys (Saimiri Kashchiarensis), common marmosets (Callithrix jacchus) and a capuchin (Sapajus xanthosternos).
Capuchin monkeys are the only New World monkeys that can hold their thumbs close to their index or middle fingers with precision. The squirrel monkey’s thumb is opposable, but it cannot be moved freely or grasped accurately. Marmosets, on the other hand, are better suited to climbing thick, vertical tree trunks, so they don’t have anything like opposable thumbs.
The monkeys were trained to watch Garcia Peregrine handle food and choose which of his fists contained the reward. He then performed a trick called the French drop by showing the food in one hand and passing it to the other or pretending to grab it and hold it in the same hand.
Both the capuchin and squirrel monkey correctly chose the rewarding hand when the actual transfer was made, but were fooled by the French drop. Marmosets, by contrast, never fell for the trick, but were tricked when the reward actually went into another hand.
Garcia-Peregrine and his colleagues conclude that capuchins and squirrel monkeys were familiar with the magician’s anatomy, so they could have predicted the magician’s hand movements and were thus deceived. “This shows that our internal biases regarding movement can be misleading, and this seems to be common in other primates,” he says Garcia-Pelegrin. “This seems to be exploited by magicians by presenting these cues, but it seems to alter the outcome of the movement. Magicians can trick us, and so can monkeys.” seems to be
“The most important takeaway from the research is that hand movements are very important as social cues. Accurately model movement.
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