The tears

Why do we have tears. We have tears of happiness and tears of joy as well as tears sadness and or sorrow. How is it that our bodies know what tears are appropriate for what scenario, and how do others know what the tears are that we are dispensing and the reason for them?. Do they know by the look we have in our eyes and or the emotion that we may be displaying on our face at the time they are looking at us!. Why is it that we shed these tears from our bodies during the Times of happiness and or joy or sorrow or sadness. Why is it that we do not simply have a more non-verbal gesture during these times like clapping our hands or simply a frown or a smile instead. Or is it simply that we have not been taught to show these emotions so we simply shed these little drops of water from our ever gazing eyes. Also why is it that in Times of deep pain/sorrow like in a death or in Times of great happiness such as a birth of a new baby for new parents they both almost at the same time start to cry; cry the tears of happiness or sadness at the same time?. Is it simply the emotional sharing between the people or is it something more like a chemical reaction that is being shared between them that makes them cry!. Is this something that can be answered or simply another mystery for the ages that may never be answered?.