My theory is that over millennia homo sapiens ( or whichever 'homo' - erectus, neandertalensis, floresiensis, etc - first developed conscious awareness ) developed a stronger and wider set of memories. This biped was intensely sociable and communicative, and began to need to remember bigger and bigger groups of its fellow-creatures and their characteristics ( eg, meekness, ferocity, greed, etc) and their relationships, in order to fit in and get on with everyone. I think these memories and the grasp of social situations gradually came to form some kind of early awareness, which then grew exponentially. But you have to realise that an awful lot of authors have written an awful lot of tosh about human awareness/ consciousness/intelligence. So read all the books, and take them all with several tons of salt.