Awareness of Past and Future
"Past" and "Future" are intrinsically deictic categories, that is, they are defined relative to the category "Now". Notions of "Past" and "Future", therefore, can only exist if a construal for "Now" can be produced. In the case of humans, it is not clear that operating with the three-category distinction Past-Now-Future is a human universal. For example, it has been claimed that the Aymara of the Andes did not operate with a distinct concept of "Now" before contact with Europeans. It seems that they operated with a well-known bi-categorical schema realis-irrealis, which in their case meant "known times" (i.e., corresponding to the Western "Past and Now"), and "unknown times" (corresponding to "Future" times). The fact that the notion of "now" (and therefore the notions of "future" and "past") may not be a human universal should not be a surprise in that it is a relatively complex idea. For instance, even in ordinary everyday language it is highly polysemous with respect to temporal extension: it can mean an instant, a day, a week, a year, a month, a century, a millenium, and so on.
There is another time system that is not deictic (and therefore does not require a "Now"), which manifests itself in the temporal relations "later than" and "earlier than". This system is logically and semantically simpler, and it seems to appear earlier in human development than the deictic form "Past-Now-Future".
Awareness of Earlier events and of Later ones (sometimes called Mental time travel) is the cognitive capability of remembering events that already occurred and predicting events that have not occurred yet. There is some indirect evidence of such abilities in nonhuman animals. For example, blue jays (Cyanocitta cristata) are important dispersers of Quercus, Fagus, and Castanea nuts in eastern North America and their caching behavior in the wild has been well documented. Chimpanzees make and use tools for foraging. In some cases they prepare the tools before they reach to the destination. This, however, is mainly within relatively short temporal spans. How far can they imagine times that occurred and times that have not occurred yet is not known? This is a question open to further studies.