Swans are used as symbol of love because once they find there partner they spend the rest of there lives with each other. Human beings apparently have this function as well, scientists found that a chemical is produced in the brain which causes devotion in humans once a physical bond has occured. I suppose when humans get too greedy and want multiple partners in a sense are going against God too. However, Islam justifies multiple wives which I feel is shame to the ladies because jealousy is also a natural human emotion, this might be an example how greed made its way in religion!?. Or maybe I have it wrong?