First, I'll start by saying that the previous responses are excellent, and are probably better than the one I'm about to post regarding your questions. I'm going to piggyback off of Rand's perspective on emotion by describing it in my own way, because in my opinion (regarding her views on emotion, I thought she was accurate):
Emotions, in my opinion, are physiological responses to any event, person, image or object valued by the subject experiencing the succeeding feeling. The origin of this response, as previously pointed out by others, more than likely originates from an evolutionary background. However, the attributed value is very important to recognize as well. For instance, two different people can listen to one song and "feel" or rather, have different emotional responses after hearing that song. This is due to the value or deeply subconscious values each subject holds to that medium (which is the music). This is heavily related to language and symbol recognition as well, and it is perfectly reasonable to argue over the origination of those values to begin with.
Another, perhaps more concrete and personal example are those responses of two different married men that I know of. Both of their wives committed adultery, and yet the responses from each man was completely different! My friend, who is one of the men I am talking about, was completely devastated when he found out about his wife's action. The other however, literally, simply shrugged it off and gladly proceeded to sign the divorce documents. Basically you have two different individuals facing the same objective reality (wife cheating), and yet they react to this in radically different ways because the value of their wives were completely different. There are many more concrete examples but I'm not trying to sound like a broken record here lol
Anyway, I only think I answered your first two questions, because the other questions that follow are much more complicated in my opinion, and would take much more time and research to answer (for me at least).
