Mental Time Travel:

Thomas Suddendorf, An Evolutionary Perspective on Mental Time Travel (2020)


Wild animals run from the dangers they actually see, and once they have escaped them worry no more. We however are tormented alike by what is past and what is to come.

—Seneca


"The notion that humans are unique in their mental access to past and future has featured in the writings of diverse philosophers, from Seneca to Schopenhauer. When the modern concept of “mental time travel” was introduced, its evolution and the potential discontinuity between human and nonhuman cognition featured centrally (Suddendorf & Corballis, 1997). However, the initial review also showed that, although the available evidence was in line with the basic assumption of human uniqueness, there were in truth relatively few relevant scientic studies on animals. This has changed, as over the last couple of decades researchers have increasingly put animal capacities to the test and the nature of mental time travel has become a hot topic of debate in diverse disciplines. This article examines the nature of mental time travel and reviews evidence for similar capacities in nonhuman animals. Some of the literature has somewhat partisan overtones that seem to either want to brush aside signs of discontinuity in order to highlight evidence of continuity between human and nonhuman capacities, or to belittle evidence for continuity to emphasize human uniqueness. Naturally, the scientic endeavor should avoid being inuenced by such biases. But leanings exist and appear at times to be exacerbated by a confusion about the dierence between evolutionary continuities and present continuities. Darwin’s theory of descent with modication assumes gradual changes over evolutionary time, and there are no reasons to suppose that the capacity to travel mentally in time evolved in any other way. In line with such evolutionary continuity, there is no doubt that the human faculty draws on many cognitive (e.g., working memory) and neuronal resources (e.g., the hippocampus) that are similar in our animal relatives because we share common descent. After all, evolution has to tinker with what exists rather than to invent traits de novo. However, this does not preclude the possibility that some important differences, even attributes that appear to differ in kind, may also exist in this domain (Suddendorf, 2013a). First of all, gradual changes can bring about radical transformations. A favorite illustration of this is that as temperature gradually increases, the properties of H2O are altered dramatically as it changes from a solid, to a liquid, to a gas. Similarly, gradual increase in, for instance, working memory capacity, can lead to dramatic transformations in what cognitive operations one can engage in (e.g., Halford, Wilson, & Phillips, 1998). Secondly, and most importantly, note that transitional forms can go extinct and indeed most species that ever existed are extinct. Therefore, gradually evolved traits can still appear to be dramatically distinct compared to what presently exists in closely related species. In other words, evolutionary continuity need not equate to present continuities. Many species of smart upright-walking hominins used to roam this planet (e.g., Robson & Wood, 2008) and might have demonstrated gradual differences in mental time travel capacities. But their extinctions leave modern humans as the only surviving species of this group with a few traits that appear to be discontinuous from anything we can find in our closest surviving relatives (Suddendorf, 2013a). As will become evident in this review, recent research has demonstrated some exciting competences in other animals that highlight continuity in the evolution of memory and prospection. Nonetheless, it still seems to be the case that there is something fundamentally distinct about human mental time travel when compared to the capacities of our closest surviving animal relatives (even as we are searching for what precisely the limiting factors are). The emergence of a fully-edged capacity for mental time travel opened the door to powerful new opportunities in our forebears, including our potent ability to shape our own future skill sets."