Close your eyes and imagine what tomorrow is going to be like. You might not get it completely right, but you can probably sketch out a good approximation—when you wake up, how you get your coffee, getting the kids ready for school, feeding the dog, who you talk to at work or at home. It’s not hard to imagine what it might be like with some level of confidence.
For decades, some experts in psychology have argued that the imagining you just did—called “mental time travel”—is one of the things that makes humans special.
The concept was introduced in the 1980s by a psychologist named Endel Tulving, who focused his work on humans and found that people with certain kinds of brain injuries cannot engage in this kind of future imagining. The idea that mental time travel is unique to humans and “is one of the reasons humans have been able to dominate the environment and many other species on this planet,” as psychologist Jonathan Redshaw wrote in one paper, persists today.
But is it true? Psychologists and researchers who explore this question are divided. And the rift between them can teach us something about how we do science, how we think about animals, and how we might better think about the future.
Those who hold that the ability to move into the future in our minds is uniquely human believe we should assume, at a baseline, that humans are special. Researcher Thomas Suddendorf, author of a seminal 2007 paper on the topic, argues that this is simply good science. “While our children’s books and cartoons are full of stories of animals plotting the future, we are not bombarded with accounts of real animals in forests or farms, say, working to foil the bad guy’s evil plot, or of them scheming to escape from the zoo next summer when the conditions are right,” he told me via email. “So it would seem more sensible to start from the assumption of absence, and then set out to try to falsify that claim through studies that demonstrate competence.”
And yet, over the past few decades, research has shown that nonhuman animals are far more capable, aware, and intelligent than we once thought. Pigs can be optimistic or pessimistic, giraffes can use statistical reasoning, even cuttlefish can remember what, where, and when. Humans are, after all, animals too, and we’re linked by evolution. If there is a benefit to foresight, you might expect that evolution would encourage its development in other creatures as well. In fact, human children don’t seem to develop this skill until they’re about 4 years old. It seems a bit strange to assume that just because animals don't behave as they do in children’s books they aren’t capable of higher-level reasoning or imagining the future. (See the classic Onion article “Study: Dolphins, Not So Intelligent on Land.”)
But perhaps a bigger problem lies in the way this debate has been set up. Some experts in mental time travel define it in such a way that the question of whether other animals are capable is unanswerable. These folks argue that for a creature to truly have mental time travel, it must have what they call “phenomenological experience,” which is essentially consciousness and awareness of the mental process. The problem is that this experience is internal and private. You and I can’t know another human’s internal state of consciousness without asking (and sometimes even with asking). Without being able to have a long, philosophical chat with a creature about its internal state, we will never know if rats or birds or dolphins or monkeys have this ability. (I am reminded of research I did years ago on the debate over whether it was scientifically sound to say that individual animals had “personalities.” One researcher told me that you simply couldn’t say so because it has “person” in the word.)
These two issues combined make some angles of exploring the question of human uniqueness in mental time travel a nonstarter. Even in the 2007 issue of Behavioral Brain Science, Suddendorf and coauthor Michael C. Corbalis got pushback, with some arguing that “searching for a yes or no answer to a question about human uniqueness is not a productive way to proceed with research in comparative cognition.”
It’s a convenient setup, though, if you like being right. “If you want to claim that this is uniquely human, then your safest terrain is to do something that's untestable. If you can't prove it, how can we ever know?” says Nicola Clayton, a researcher (and dancer) at the University of Cambridge who has spent decades researching mental time travel in corvids like scrub jays, crows, and ravens. For her purposes, Clayton has to set aside this question of internal states. “My approach has always been to look at what we could do with the animals,” she says. “It doesn’t prove anything, but you can’t prove anything in the behavioral sciences. If you want proof, then my advice would be to go study pure mathematics.”
With her approach, Clayton has found that corvids like scrub jays will hide food when another bird is watching—but only if they’ve stolen food from another bird before. In other words, if they’ve been a thief, they think about thieves while they’re caching. Her research has also found that jays understand how fast certain food items decay—worms go bad faster than nuts—and they will return to food stores that are shorter-lived quicker than those they know will last longer. Other research on rats has shown that the animals can remember where their favorite foods were in a maze, and how long they tended to last, and will return to the ones they knew would be around.
Of course, the animals could simply be driven by some kind of instinct, rather than picturing what the future might hold and planning for it. Squirrels, for example, hoard food even if they’re young and have not yet experienced a winter, which suggests that they’re not planning for the future based on past experience. Animals in the lab could just be trained to do the thing scientists want, without really understanding why they’re doing it.
This is known, sometimes, as Morgan’s canon, a rule in psychology put forth by British researcher C. Lloyd Morgan in the late 19th century, which states that animal behavior shouldn’t be interpreted through the lens of higher psychological processes “if it can be fairly interpreted in terms of processes which stand lower in the scale of psychological evolution and development.” Morgan himself later tempered that statement, saying “there is nothing really wrong with complex interpretations if an animal species has provided independent signs of high intelligence.” But often the rule is trotted out to remind researchers not to assume that any species other than humanity is capable of complex thought.
Clayton, and others who believe that animals are capable of thinking ahead, say they don’t believe every animal is plotting its next move based on memory. But some, certainly, do seem to be able to take past memories and turn them into foresight. And Clayton’s work, along with that of others, has managed to convince a lot of former skeptics. About 10 years ago, one of the coauthors of the original paper positing mental time travel as a uniquely human ability, Corballis, changed his mind.
Corballis passed away in 2021, but in the paper in which he declared his changed opinion, he wrote about an experiment with rats in which rat brains showed activity in the hippocampus not only when they were in a particular location, but also later on when they were taken out of the maze. “This suggests that mental time travel has neuro-physiological underpinnings that go far back in evolution, and may not be, as some (including myself) have claimed, unique to humans,” he wrote.
Suddendorf, who remained unconvinced by the rat and jay experiments, recently collaborated on a paper with Clayton about New Caledonian crows and their ability to plan for future tool use. “We designed an experiment together to address the issues he was worried about,” Clayton says, “and then we let the New Caledonian crows do what they damn well please, because that’s the best way to deal with corvids.” In the study, they presented the crows with a little puzzle that required a tool to “solve” and, when solved, would reward them with food. The crows were shown the problem, and then five minutes later shown a set of tools that they could select from to solve the puzzle. Ten minutes after that, they were given access to the puzzle. If the crows could plan for the future, they’d pick the right tool to use and ignore the tools that they knew wouldn’t work. And in the study, that’s exactly what they did.
But Suddendorf says he hasn’t necessarily been convinced of anything just yet. “This is promising, and we will need to do further studies to clarify the nature of this competence,” he told me. “As yet there is no compelling evidence that other animals envision remote events, reflect on mutually exclusive possibilities, or that they embed mental nesting scenarios into larger narratives.”
Setting aside untestable definitions of this skill, it does seem as though once again, something that humans thought to be unique to our species is perhaps not quite so special. Maybe Western scientists should reconsider the assumption that humans are set apart and uniquely equipped with mental tools no other living thing has. This story has repeated itself a lot in science—animals continually prove themselves to be more capable than humans have given them credit for. And in this case I think we can learn more from it than just “don’t underestimate other animals.” Perhaps we can actually learn about how to engage in our own futurism, by looking at what these other species do.
