The sense of self is a question that only the leisure can create. Ray Kurzweil contributes greatly to this topic. You need a certain amount of time available to be able to give shape to that abstraction, defined by scholars such as cognitive. In times in which men should spend most of the time trying to survive at a fraught with adverse nature of hazards with also acute mortality, the meaning of existence is impersonated by the subsistence. The progress of man is accompanied with brutality and the mastery of the medium, also wasteful. This advance gave him time for reflection, and this led him to consider ontological philosophical questions (of being) as who am I?, what is my purpose in this world?, the origin and the meaning of things, among thousands of other concerns. Before the Greeks, the Orientals advocate the negation of that being to reach an overcoming, but for something it is refused it must exist, even in thought. The Zen method is a clear for example, Buddhism tries to an overcoming of the soul on the body also denying the material but uses a purification process quite complex, in which fasting has an important part, and can that that physical weakness due to lack of nutrients will lead to hallucinations.
Known tribes of Celtic, African and American experienced with drugs in search of answers to the meaning of existence. The obtained answers are as varied as their rites but the provenance of a governing animal is a constant, is seen in the hallucination or poisoning induced, an animal that is which governs the experimenter. The Greeks are the first to raise the sense of existence as we know it. Our beliefs are affected by this logic, theoretical and pragmatic thinking of search. Our society despite centuries separating us is dominated by values that were born at that time and in that culture.