Helen Fisher

Jealousy can even be good for love. One partner may feel secretly flattered when the other is mildly jealous. And catching someone flirting with your beloved can spark the kind of lust and romance that reignites a relationship.

Why do we feel jealousy? Therapists often regard the demon as a scar of childhood trauma or a symptom of a psychological problem. And it's true that people who feel inadequate, insecure, or overly dependent tend to be more jealous than others.

A hundred years ago, if you had a child out of marriage, you'd be a social disgrace. Today women feel comfortable enough economically and culturally to bring up a child without a recognized commitment from a man.

Despite the myth that men are less committed, they are predisposed to desire marriage.

In America, we are demanding everything from our marriage.

There's a lot of talk about the positive aspects of love. We as a society downplay the danger, the anxiety, and the disappointment. We romanticize romance.

A lot of people head into courtship looking for fireworks. Don't pass up a chance by dumping someone after a first date because you don't feel the fireworks. The fireworks can happen at any time and be maintained.

Today, most women are surrounded by ingenious gadgets. They don't grow the peas or raise the chicken that they serve for dinner; instead they hunt and gather in the grocery store. They go through catalogs or department stores to buy clothes instead of shearing sheep, carding wool, and weaving cloth for skirts and coats and blankets.

Men have a psychological need to show off their courage and strength. When he sees you talking to another guy, that instinct kicks in and he jumps to protect you and prove he's worthy of your love.

Your sweetheart calls you by another's name. His eyes linger too long on your best friend. He talks with excitement about a girl at work. And the fire catches. Jealousy - that sickening combination of possessiveness, suspicion, rage, and humiliation - can overtake your mind and threaten your very core as you contemplate your rival.

Both sexes like the exercise and challenge of sports, but for men it's also a basic display behavior for impressing and winning a mate.

If two very different people pool their DNA, they'll create more genetic variety, and their young will come to the job of parenting with a wider array of skills.

Men with high baseline levels of testosterone marry less frequently, have more adulterous affairs, commit more spousal abuse, and divorce more often.