As a human, I guess many of us will experience that sometimes we have uncontrollable desires, be it in our heart or in our mind. We tend to want something beyond our basic needs and move up the Maslow’s Hierarchy of Needs. And, again, being human, we are likely to never feel satisfied with what we have and keep wanting more and more.
Then, when we (sometimes unconsciously) become afraid of losing what we have, it is when jealousy comes in.
Based on what I found in Wikipedia,