From the mid-1990s, spurred by a PhD student from Germany called Thomas Suddendorf, I developed an interest in mental time travel - the ability to mentally relive past events and imagine future ones. For a while, we accepted the common belief that only humans are capable of mental time travel. Other animals are stuck in the present. This belief, though, was strongly challenged by behavioural evidence, and by indications that the hippocampal formation in the brain allows mental time travel, even in rats. I changed my view, arguing that mental time travel goes far back in evolution. It also provides for generative imagination, and may be critical to the later evolution of language.