Have you ever known a married couple that just didn't seem as though they should fit together -- yet they are both happy in the marriage, and you can't figure out why?

What mysterious force drives us into the arms of one person, while pushing us away from another who might appear equally desirable to any unbiased observer?

Of the many factors influencing our idea of the perfect mate, one of the most telling is our "love map" -- a group of messages encoded in our brains that describes our likes and dislikes. It shows our preferences in hair and eye color, in voice, smell, body build. It also records the kind of personality that appeals to us, whether it's the warm and friendly type or the strong, silent type.

In short, we fall for and pursue those people who most clearly fit our love map. And this love map is largely determined in childhood. By age eight, the pattern for our ideal mate has already begun to float around in our brains.

Researchers find that that there are many similarities between our ideal mates and our moms. Yes, our mothers -- the first real love of our lives -- write a significant portion of our love map.

When we're little, our mother is the center of our attention, and we are the center of hers. So our mother's characteristics leave an indelible impression, and we are forever attracted to people with her facial features, body type, personality, even sense of humor.

The mother has an additional influence on her sons: she not only gives them clues to what they will find attractive in a mate, but also affects how they feel about women in general.

Just as mothers influence their son's general feelings toward women, fathers influence their daughter's general feelings about men.

In addition, most of us grow up with people of similar social circumstances. We hang around with people in the same town; our friends have about the same educational backgrounds and career goals. We tend to be most comfortable with these people, and therefore we tend to link up with others whose families are often much like our own.

What about opposites? Are they really attracted to each other? Yes and no. In many ways we want a mirror image of ourselves. Physically attractive people, for example, are usually drawn to a partner who's equally attractive.

Robert Winch, a longtime sociology professor at Northwestern University, stated in his research that our choice of a marriage partner involves a number of social similarities. But he also maintained that we look for someone with complementary needs. A talker is attracted to someone who likes to listen, or an aggressive personality may seek out a more passive partner.

As Winch observed, it's the balancing out of sociological likenesses and psychological differences that seems to point the way for the most solid lifelong romance.

Is there such a thing as love at first sight? Why not? When people become love-struck, what happens in that instant is the couple probably discover a unique something they have in common. It could be something as mundane as they both were reading the same book or were born in the same town. At the same time they recognize some trait in the other that complements their own personality.