The great apes can remember events that happened years ago just like men and women do, researchers have found.
As with humans, a reminder of something in the distant past can jog the memories of chimps and orangutans.
Scientists took a group of apes and reconstructed a series of experiments conducted three years previously in which they had had to find hidden tools that could be used to reach food.
Faced with the same set up of rooms and boxes in which the tools were concealed, the apes immediately knew what to do. It took them only five seconds to find the tools.
Another group of apes which had not had the previous experience were left confused.