Written by Ericka Souter on CafeMom's blog, The Stir.

As a child, I was always mystified by those girls who always wanted to play "Mommy" or "House." It just never held the same allure to me. Sure, I liked Barbies, but I was pretending they were flying around the world or solving mysteries, not having babies or getting married to Ken.

In my 20's, I was equally bewildered by all the women I met who dreamed of being moms more than career women and those that actually felt that it was what they were meant to do. Totally, freaking baffling to me. I just never got it. I know I'm not alone.

In the world of mothers, I have learned there are two kinds -- women who love being a mom but honestly believe they would feel no less complete if they weren't and those who could not imagine being anything else. And now I know why.

There may be such a thing as a "mom gene," according to a research study out of Rockefeller University in New York. Their conclusion: Some of us are born with the unrelenting need to mother and some of us just aren't. Of course that doesn't mean those without it are not capable of being loving, nurturing moms. We can be and we are. It's just not so... innate.

This, of course, flies in the face of popular thinking. There is so much pressure to have kids in our society. The first question out of everyone's mouth as soon as you say 'I do': "When are you going to have kids?" Your first child will still be in diapers when the inevitable, "Thinking about another one? Don't wait too long!" comes rolling off some busybody's tongue.

Everyone assumes every woman needs to be a mother and that's just not true. I didn't need a scientific experiment to tell me that. Now in my mid-30's, I just had to look around me. I have married, successful, financially stable friends whose biological clocks never started ticking. There is no maternal longing in their eyes. They don't want kids and seem very content with that choice.

Though that is something my very old-fashioned mother-in-law refuses to believe. She insists that every woman wants to have a baby. Whenever a childless friend comes over, she throws my toddler in their arms, waiting expectantly for the gushing, cooing, and "I can't wait to be a mom" pronouncements. And even when it doesn't happen, she still insists that so-and-so wants to be a mom.

She represents how most of society feels. They just can't accept that some of us weren't born to be moms. I, however, totally buy into this whole idea of a "mom gene." Motherhood is wonderful and I wouldn't change my membership in that club for anything in the world. But the bottom line is that some women know it's what they want from the start, others realize the wonders of it once it happens and for many others, it's just not part of their makeup at all -- and there's nothing wrong with that

Do you think there is a mom gene?