even if the whole world itself is one self, 'self' is only a word to describe the filter or instrument through which we experience life.
it is the closest word i could find to express myself. all words are at least once removed from the idea. i think, if you are disagreeing with me, it could be more a matter of semantics than contrary belief.
never the same self with other selves- are you referring to the masks we wear in others' company ?
i think selfishness comes out of instinctual self-preservation.. a sort of reflex that works but eventually becomes burdensome and detrimental to wellbeing.. its something all too easily learned but not so easily unlearned
yes (for your first paragraphe) although it's an interesting question, whether different faces are masks we put on, or simply/honestly different "us", cause we react differently to every different person... for example, do you know people who are "X" in one place/company, and completely different in another circumstances? I know many... or myself
I think selfishness is many times depends of personality and/or breeding (education)... the good side of selfishness (in my view) - there is no other way to reach/obtain big achievements sometimes even love
and yeah on the 'different us' bit... its like the question: what is unnatural? if you believe everything comes out of nature.. how could nature produce something other than itself? if we, humans, are of nature, what we produce is of nature, yeah? i dunno, can give me a headache to think about.