Jealousy Is A Curse

Why is it that people get jealous? What causes us as humans to be jealous? I decided to look up the definition of jealousy and this is what dictionary.com states:

noun, plural jeal·ous·ies for 4. jealous resentment against a rival, a person enjoying success or advantage, etc., or against another's success or advantage itself. mental uneasiness from suspicion or fear of rivalry, unfaithfulness, etc., as in love or aims.vigilance in maintaining or guarding something. a jealous feeling, disposition, state, or mood.

I, myself know that I have been jealous before, but I am learning that I don't need to be jealous of anyone. Just because others are more well off than me, doesn't mean that they are actually more better off mentally or spiritually. You don't need money and all the expensive crap to be happy. You create your own happiness from within. Material objects will never make someone truly happy, so why be jealous of those that do have all those material objects. I would rather be poor than be jealous of some of these people with enough money to buy whatever they want. 

I'm also noticing that with particular people it doesn't matter if you have done well with an exam or if you have achieved something, they will never be genuinely happy for you, they are jealous because you did well at something. They will one day realise that all that jealousy has got them nowhere and they probably won't have much inner peace either. I am starting to wonder if a lot of the jealousy that does occur now is because of social media and how people are always on there boasting about how great their life is and how much money they are making or an expensive (non essential item) they have purchased. Every time that I look at social media it is a celebrity or someone who is basically saying look at me. Then all these people get jealous and want whatever that person has. I grew up in a family that at the time would have been considered 'well off'. I had things that a lot of other kids didn't have. But I felt blessed because I had those things, not wanting to show them off to every single person that I know. It may also come down to the generations, I guess any generation after Gen X is probably quite the jealous type and extremely materialistic.

What generation are you and are you materialistic and do you get jealous of other easily and if so, what do you get jealous over?