What causes jealousy?

I have to say, I don't have the complete answer to that, but what I do know is that jealousy is usually caused by insecurity. A lot of people today (more referring to pre teen and teenage girls) suffer jealousy for many reasons. Usually it is girls who either think another girl is prettier than them, maybe more talented, etc. In any way, jealousy can be very painful, if not dangerous to our society today. *Jealousy's main cause is girls [or boys] who feel insecure about themselves. Jealousy is very natural but we do need to learn how to control this emotion which is the hard part, many people suffer because of something that has hurt them or it can be because of some fear do to a past terrible experience or relationship. When something happens that reminds us of it again it causes a fear, anger and jealousy. It's all related somehow.