Our ability to recall past events in our lives is part of what has come to be called mental time travel. Our memories, however imperfect, probably evolved not to provide a faithful record of the past, but rather to supply information for building future scenarios. This allows us to plan events in detail, or to weigh up different possibilities before the future is upon us. It also enables us to create what have been called “future selves”, models of what we hope to become once we have completed an education, found a mate, bought a house, chosen a career or cleaned out the basement.
Like Browning’s grammarian, a number of cognitive scientists, myself among them, have controversially claimed that only humans can travel mentally in time. Animal researchers have risen to the challenge, but it has proven peculiarly difficult to show that non-human animals can indeed mentally relive the past or imagine the future. In humans, of course, we can simply ask, but in animals lacking language we need other techniques. The problem isn’t simple. Consider for example a dog that buries a bone, and later returns to dig it up. This need not mean that it actually remembers burying the bone. It may simply have knowledge of where the bone is buried, without mentally reliving the act itself.
One suggestion is that we could be surer of true remembering if we could show that an animal that buries food can recollect not only what is buried and where it is buried, but also when it was buried. Scrub jays, pesky little birds that cache food for later consumption, may well pass this what-where-when test (also called the www test). If they cache both worms and nuts in different places, they will recover the worms if a relatively short time has elapsed, since they prefer fresh worms to nuts. But if a longer time has elapsed, they will go for the nuts, evidently because they know the worms will no longer be fresh. This suggests that they remember not only what they cached and where they cached it, but also when they cached it.
Moreover, if jays are watched by another while caching food, they later re-cache it, presumably to thwart the watching bird from stealing the food. But they will only re-cache if they themselves have stolen food; even in scrub jays, it takes a thief to know a thief. Re-caching might be taken as evidence that the birds can imagine a future event of theft.
These are among the increasingly clever experiments designed to show that nonhuman species can travel mentally in time. But I’m not yet convinced. My knowledge of such events as my own birth passes the www test—I know where I was born, when I was born and, heaven help me, what was born, but of course I have no actual memory of the event. The critical distinction is between what we know and what we actually remember, and it remains a real challenge to demonstrate that distinction in birds, or in any non-human species. I invite suggestions.
Be that as it may, there can be no doubt that we humans are obsessed with time. Of course other animals plan for the future by migrating or by hoarding food, but these activities are instinctive, driven by changes of season, and have limited provenance. In our own activities we are driven by time itself, with appointments, deadlines, wedding anniversaries and taxes. Although generally adaptive, reliving the past can be an emotional hazard, as when we recall previous embarrassment, and anticipation of the future can be a source of anxiety, as in a visit to the dentist or an appointment with the boss—or the inevitability of death, leading perhaps to religions that promise an after-life. Sometimes, though, the knowledge that time will pass is a comfort, as when Viola in Shakespeare’s Twelfth Night, masquerading as a man, finds herself in an impossible situation and exclaims:
O Time, thou must untangle this, not I;
It is too hard a knot for me t’untie!
Language itself may have evolved precisely to allow us to share our experiences, and its lack in other species may reflect the absence of mental time travel. Sharing allows us to benefit from the memories and plans of others. And to be adaptive, the tales we tell need not be true. This explains not only our predilection for gossip and shared confidences,but also the human obsession with fiction, whether through stories around the campfire, novels, plays or TV soaps. Or, you may think,columns like this.