"Karen practically lives here anyway," I explained, "so we figured, why should she be paying rent when we could all be picking up equity on a bigger house?" John kicked me under the table. He's never been able to break me of babbling to strangers. Once someone sits down in our kitchen, I might as well just hand them my diary and point out all the good parts.

Karen excused herself to pick up the kids from swimming lessons. John and I are their biological parents, but only my oldest child, Katie, remembers a time when Karen wasn't part of the family. The division of child-care labor mirrors our respective personalities. At any given time, I know where my children are emotionally, John knows where they are academically, and Karen knows where they are physically. She thrives on managing the detailed morass of school holidays, bus schedules, sports events and music lessons that leave John and me feeling exhausted and bewildered.

After Karen left our real-estate meeting, Myrna turned to me and beamed, "A nanny!" she said. "How wonderful! I wish I'd had another mother around when my kids were little!"

I smiled insincerely, wondering how Myrna thought I'd managed to convince a college professor my own age to work as my nanny. I didn't bother to correct the real estate agent, because I know there's not an established social category for Karen. I've heard my children introduce her to friends as their "godmother." Though this isn't true in the technical, religious sense of the word, it certainly conveys the right meaning. If I am the mother whom nature gave my children -- that would be "nature red in tooth and claw" -- Karen is the one furnished by an improbable, benevolent higher power. I am consciously aware of this, because, truth be told, Karen isn't just my children's "other mother." She's mine too.

I come from a long line of maternally challenged women. My mother had eight children, spreading her pregnancies from one end of the baby boom to the other. I was born seventh. After my younger sister came along, when I was still less than two years old, my mother went to bed for a well-earned rest. I'm not sure she's gotten up yet. She figures in my childhood memories as an exhausted, mostly horizontal figure, visibly overwhelmed by the endless needs of the horde she had conceived and delivered.

Compared to the woman who raised her, however, my mom was the Madonna. My grandmother, a spiteful, paranoid bigot we called Groin Murder, is the only person I've ever known who flunked nursing home. She was so nasty that no one would room with her, and the officials sent her home. (They eventually called back, having found the perfect roommate for Groin Murder: a woman whose long-term memory had been wiped out by a stroke. Until Groin Murder passed away, her roomie lived in a state of constant annoyance, but could never remember why.) Even so, I don't really hold Groin Murder responsible for her flagrant emotional inadequacy. Her mother died in childbirth, when Groin Murder was only three. In my family history, as in most such dismal legacies, there are many people to pity, but none to blame.

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