A new study shows chimpanzees and orangutans having the ability to remember distant events based on key sensory items, BBC News reported.
In an experiment, both species successfully found a tool hidden three years after performing a task only four times. Both were presented two boxes, each in separate rooms, one box with useful tools and one box with un-useful tools.
The tools were hidden without the animals' knowledge and, three years later, they were able to retrieve the useful tools.
This was a trait previously thought to be exclusive to humans, but the primates were able to remember where the useful tools were because the environment where they experienced the event had gone unchanged. Similarly, a smell, a sound or even a glimpse of something can trigger distant memories in humans.
Lead author of the study, published in Current Biology, Gema Martin-Ordas of Aarhus University in Denmark, used that principle for her experiment.
"Our data, and other emerging evidence, keep challenging the idea of non-human animals being stuck in time," said Dr. Martin-Ordas. "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."
Her team found that 90 percent of the primates who experienced the event three years ago were able to locate the correct tools almost instantly.
"What this shows is that the episodic memory system in humans is not as unique as we thought it was, as we share features with non-human primates," Martin-Ordas said.
Michael Corballis, of the University of Auckland in New Zealand, was not affiliated with the study but said the results prove what many had not previously accepted. The only difference between human and ape memory is that human's can apply an aspect of "when" in their memories.
"There is no indication that the animals remembered when the earlier event occurred. 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," he said. "My guess is that great apes, and perhaps even rats, have episodic memories similar to our own, probably less rich and detailed, but similar in essence."
