Chimpanzees and orangutans remember distant, past events if prompted with sensory reminders, a new study published in Current Biology finds. Recalling memories was previously thought to be unique to humans.
Three years ago, the animals had to perform a task four times. Both species were given two boxes in different rooms, one containing useful tools, and the other containing useless ones. To receive an award, the primates had to retrieve the useful tools from where they were hidden.
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The majority of the group — 90 percent — successfully located where the useful tools had been placed since they last saw them without watching where the researchers planted them, the BBC reported.
The apes’ memory was triggered by cues that were kept the same in previous experiment, according to the study’s lead researcher, Dr. Gema Martin-Ordas of Denmark’s Aarhus University.
"Our data, and other emerging evidence, keep challenging the idea of nonhuman animals being stuck in time," Martin-Ordas told the BBC.
"We show not only that chimpanzees and orangutans remember events that happened two weeks or three years ago, but also that they can remember them even when they are not expecting to have to recall those events at a later time, " Martin-Ordas added.
In a separate experiment, the primates were also able to remember a unique event that occurred two weeks prior.
Martin-Ordas concluded through the study that "the episodic memory system in humans is not as unique as we thought it was, as we share features with nonhuman primates."
Michael Corballis, a leading psychological science professor from the University of Auckland, New Zealand, who was not involved with the study, pointed out that while the apes are able to recall the what and where of a past event, they are missing the "when" component, according to the BBC.
"There is no indication that the animals remembered when the earlier event occurred," Corballis said. "This is not to say the animals had no inkling of this, and in any case we humans are often hazy about the locations of events in time."
Corballis guessed that "great apes, and perhaps even rats, have episodic memories similar to our own, probably less rich and detailed, but similar in essence."
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