We humans can remember events in our lives that happened years ago, with those memories often surfacing unexpectedly in response to sensory triggers: perhaps a unique flavor or scent. Now, researchers reporting in Current Biology, a Cell Press publication, on July 18 have evidence to suggest that chimpanzees and orangutans have similar capacities. In laboratory tests, both primate species were clearly able to recollect a tool-finding event that they had experienced just four times three years earlier and a singular event from two weeks before, the researchers show.

It seems we have more in common with our primate cousins than we thought, specifically when it comes to our autobiographical memories, the researchers say.

"Our data and other emerging evidence keep challenging the idea of non-human animals being stuck in time," says Gema Martin-Ordas of Aarhus University in Denmark. "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."

The chimpanzees and orangutans in the study could also distinguish between similar past events in which the same tasks, locations, and people were involved, she adds. "This is a crucial finding since it implies that our subjects were able to bind the different elements of very similar events--including task, tool, experimenter. This idea of 'binding' has been considered to be a crucial component of autobiographical memories."

When presented with a particular setup, chimpanzees and orangutans instantaneously remembered where to search for tools and the location of a tool they had seen only once. The researchers note in particular the complexity and speed of the primates' recall ability.

"I was surprised to find out not only that they remembered the event that took place three years ago, but also that they did it so fast!" Martin-Ordas says. "On average it took them five seconds to go and find the tools. Again this is very telling because it shows that they were not just walking around the rooms and suddenly saw the boxes and searched for the tools inside them. More probably, it was the recalled event that enabled them to find the tools directly."

She says the new findings are just the beginning of a completely new line of research on memories for past events in non-human animals.

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Current Biology, Martin-Ordas et al.: "Memory for distant past events in chimpanzees and orangutans."