Tools, treats, toys : what human and non-human primates remember about their past and plan for their future

Abstract

Whether humans are the only species capable of re-experiencing past personal episodes and imagining potential future events has been questioned. A major obstacle previously hindering investigation of other species was that humans typically report these abilities verbally. In the past 20 years, behavioural tests pioneered on corvids and recently used with rodents have however shown, that some animals can remember details of past events and plan for future ones, albeit in a more limited way than humans. Although considered the cornerstones of human cognition, surprisingly little attention has been devoted towards investigating these prospective and retrospective abilities in other primates. I utilised behavioural methods successfully used with corvids and adapted them to fill in gaps in our knowledge concerning the presence of these abilities in three different primate taxa, by testing representative species of monkeys and apes as well as humans. I found that although long-tailed macaques may have some prospective abilities these are inferior to those previously shown by great apes. The extent of chimpanzee retrospective abilities remains inconclusive as they in my study did not use memory to find rewards but developed a strategy of choosing hiding locations that delivered most rewards earlier in testing. I also found that while children at the age of four can remember some details of past events, their retrospective abilities are not fully developed until about the age of five. Placing my findings in context with previous knowledge, apes show better performance than monkeys on both prospective and retrospective abilities, while children from about five years on show comparable prospective abilities with apes and show better performance then apes concerning retrospection.