The irony is that it all began as a plea for child support. Paula Johnson took her ex-boyfriend, Carlton Conley, to court in search of more money for 3-year-old Callie Marie.

The judge in turn ordered a paternity test. For the most part, the law says: no blood, no money. No DNA, no obligation.The paternity test proved that Carlton wasn't the biological father. But more startling was a maternity test proving that Paula wasn't the biological mother.

That's how we came to know that Callie and another little girl named Rebecca were sent home from the hospital in the arms of each other's birth mother.

All week, the headlines have read "Switched at Birth" as if this family affair were a Gilbert and Sullivan comedy. Which it is not. It's been labeled routinely as "every parent's nightmare." Which it also is not. Every parent's nightmare is the July 4 car wreck that killed Kevin Chittum and Whitney Rogers before they knew their Rebecca was born to Paula.

As reporters descended on two Virginia towns, we heard all sorts of commentators talking casually about "the wrong child" or "the wrong parents." We heard townsfolk saying how "sad" it is that two women were each "raising a child who wasn't hers."

It took a distraught Paula Johnson to set the emotional record straight when she told a packed news conference the truth about "this mistake." Sounding precisely like a distraught mother, she said of Callie, "I love her wholeheartedly, with all my heart. There isn't anything I wouldn't do for her."

It's not a surprise that the tale of the two babies has grabbed our attention. It swirls around a primal question: What exactly makes a child "ours"? The DNA we contribute or the time and love? The womb or the sweat equity?

Today nature again seems to be trumping nurture. We have developed a passion for the genetic basis of everything. We have parents seeking any high-tech method possible to have "their own" children. We have adult adoptees routinely searching for birth parents.

By and large, the law also weighs in on the side of biology. Yet we know that there is a larger duality. We know it from the experience of adoptive parents and from our own gut. Few of us can imagine "swapping" - like shoes - the child we raised and loved for the child we bore and do not know. And few of us can imagine forgetting the other child's existence.

Any court case would raise questions hard enough to stump a jury of Solomons.

Who has first dibs on an orphaned Rebecca: the biological mother or unbiological grandparents? If Rebecca belongs with her birth mother, is Callie better off with the woman who raised her? And what of the biological father? Does Carlton have rights or obligations to either of these "daughters"? Does it matter that he has been accused of battering Paula?

For that matter, what happens to the younger "sister" and older "brothers" of these girls? How on earth, finally, do we assess the best interests of these children?

With such a list, the one hope for Rebecca and Callie is for the adults to follow their original instincts. To stay as far from family court and custody fights as possible.

The choice now is between the worst of two worlds and the better of two worlds. Either both families and both daughters will be torn, wrenched apart physically or emotionally. Or a new family will be stitched carefully, extended uneasily, created and recreated one step and one visit at a time.

What makes a child "ours"? Sometimes it's genes. But it's always caring. Who do the girls "belong to"? The whole family - if they can make it work.

The Boston Globe Newspaper Co.