We're probably all hardwired for jealousy; even babies and dogs feel it. Not to be confused with envy, which is about coveting what someone else has (e.g., a fab house), jealousy is about protecting what's yours—or what you think is yours. It frequently involves a me-you-her romantic triangle and often crops up at the start of a relationship.
The Mind Game
It might not be a "jealousy center," but scientists suspect the brain's left frontal cortex, which deals in emotions like shame, is involved.
Another key player is your noggin's dopamine system; it regulates the chemical associated with happiness or reward.
Spurred by the above are the three types of jealousy:
Reactive jealousy happens after your mate has actually deceived you. You know he strayed and feel PO'ed, anxious, or sad. (Ditto if, for example, you caught your BFF out with a fun new friend.)
Suspicious jealousy rears its head when you see him flirting with someone else or if you start to doubt his commitment. Cue feelings of insecurity and distrust.
Delusional jealousy takes over when either of the above swell to the point of obsession, a la Fatal Attraction. You might act irrationally (freaking if he ogles an actress) or fanatically (creepily checking up on him).
The Body Blow
Once you're green-eyed, you might have trouble seeing anything else—quite literally. A study found that women in the throes of jealousy had trouble spotting obvious objects. The greater their jealousy, the harder time they had. (Note to self: No driving while jealous!)
Jealousy might also kick-start the body's stress response. Enter an overflow of stress hormones, spiked blood pressure, and an increased heart rate.
The End Results
Except for any delusion, these reactions could be. . .good for you. Researchers believe that jealousy evolved in humans to motivate people to protect the unions that would help them survive. (Hence, jealousy is often followed by aggression.)
In other words, jealousy is an innate part of life and no cause for embarrassment. Studies show that couples who get just a little green-eyed from time to time tend to have long, rich unions.