Short answers, pulled from the story.
Jealousy involves the wish to keep what one has, while envy is the wish to get what one does not have. Philosopher John Rawls drew this distinction, illustrating that a child is jealous of a parent's attention to a sibling but envious of a friend's new bicycle. Psychologists Laura Guerrero and Peter Andersen propose the same separation.
The word jealousy comes from the French jalousie, formed from jaloux, and before that the Low Latin zelosus, meaning full of zeal. Its deepest root is the Greek ζῆλος, which often carried a positive sense of emulation, ardour, and zeal. The same ancestor produced Italian geloso, Spanish celoso, and Portuguese cioso.
Jealousy has been observed in infants as young as five months. Research by Sybil Hart at Texas Tech University found that children are capable of feeling and displaying jealousy at as young as six months, with babies showing distress when their mothers focused attention on a lifelike doll.
Guerrero and colleagues identified six interactive responses to romantic jealousy: avoidance or denial, integrative communication, active distancing, negative affect expression, distributive communication, and violent communication or threats. They also proposed five general behavior responses, including surveillance or restriction, rival contacts, manipulation attempts, compensatory restoration, and violent behavior.
Researchers at the University of California, San Diego reported in a 2014 PLOS ONE paper that a significant number of dogs exhibited jealous behaviors when their human companions paid attention to dog-like toys, compared to non-social objects. Animal behavior consultant Mellissa Starling of the University of Sydney noted that dogs are social animals who obey a group hierarchy.
Jealousy is often presented in film as a demonstration of deep love rather than destructive obsession. Jessica R. Frampton identified 230 instances of romantic jealousy in the 51 top-grossing romantic comedies from 2002 to 2014, of which 58 percent were reactive and 31 percent possessive, with 53 percent of reactions classified as destructive.
Anthropologists have claimed that jealousy varies across cultures, with cultural learning influencing both its triggers and its expression. A study comparing Ireland, Thailand, India, and the United States found that male-dominant cultures are more likely to express jealousy, while Thais were the least likely to express it. Attitudes also shifted in the United States during the 1960s and 1970s.