Why do we have emotions?

Emotions govern our lives. Feelings like joy or anger are part of our daily experience, whilst the intensity of falling in love or suffering profound grief often stays with us for years.  But why do these emotions exist? Is there an evolutionary benefit, or are they an unavoidable by-product of our complex human brains?  Do other animals feel emotion in the same way, and what is actually happening in our bodies when love makes our hearts skip a beat or fear brings us out in a cold sweat?  What happens when emotions go wrong and we end up paralysed with fear by a tiny spider, or infatuated with a popstar that we’ve never even met?  Will we ever be able to control our emotions with science…and even if we can, should we?