In an ideal world there should be no lesions. No abrupt stoppings and re-startings, no gaps or jolts in nature's course.
The transition from youth to middle age should be governed by a smoothly unfolding process. Menopause, after all, is a gradual transition. It can last a number of years and work its ways quietly. Women's oestrogen levels decline in what feels like measured steps; periods become irregular and unpredictable, and the fuzziness can go on for such a long time it becomes the new norm. When change occurs this way, you absorb it, you adapt. Hair turns grey so gradually as to be imperceptible: one day you'll look in the mirror and be surprised by the shimmer of silver reflected back. Age will have crept up on you the way fine lines do, the way your children are suddenly grown-up, the way your parents seem suddenly old. In an ideal world this experience should feel like continuity.
This is not my story. I entered middle age all at once. There was no real menopausal process, only a Before and After. The war wounds that tell that story are arrayed across my stomach.
Four red hatch marks mark the entry points where I had keyhole surgery, and they hover above a reddish slash that looks like a half-cocked smile. It's where surgeons had to make a last-resort incision during the hysterectomy I underwent the autumn before last - a procedure that lasted some three hours and fast-tracked me into menopause. I am mesmerised by these puncture wounds, in part because they're still new and strange, with their silvery alien sheen, but also because they're so tidy; and when I think of all the mess and the blood and the proliferating outgrowths of my faulty womanhood - all the pain it caused me, and all the years I endured that fibroid pain - I cannot believe that my generative organs exited me so smartly, and without the least protest.
You cannot argue with scars. What mine tell me is that one season of my life is definitively over and another begun.
Much of the time I feel mournful, assailed by loss. I wonder if my husband, a couple of years older than me, feels similarly.
I survey him from time to time, as objectively as I can. I think he looks good. At 52, he is trim and still virile. He tries to look after himself, goes to the gym, watches his diet, and he gets as much reward out of being a dad as he does from his work (ours is a household of writers). What he mainly feels, he tells me, is a sense of urgency about his productive life potentially running out and there still being so many things he wants to accomplish.
How should he choose between projects? And how quickly can he get them done? Unlike me, he doesn't seem traumatised by his fast-disappearing youth, isn't beset by fears of stagnation: headlights locked on to the road ahead, he feels energised, and woe betide any blinking deer in his path.
Although there is no such thing as the andropause - a male equivalent to menopause when testosterone levels rapidly plummet - male testosterone levels do decline steadily with age after about 30, at a rate of roughly 2 per cent a year.
For men, the midlife crisis, if it comes, is less about biology than society. If you manage your life well, you can avoid it. If you can't, then it's time to roll out the cliches, the motorbikes, the younger girlfriends, the fast cars.
Perhaps it is worse for men, who might feel as mournful and outraged in midlife (as shocked by a transition that assigns youth squarely to the past) as women do, and yet have no clear physical culprit to pin it on. Or perhaps not. In my conversations with women, it is the decisiveness and insistence, the importuning, of biology that is the trouble. We had assumed that ageing would move over us rather like a desert wind over dunes, bringing about a gentle drift, a shift in shape that would leave our essence, our fundamental "duneness", intact. But for many women it hasn't worked that way. Ageing has punched us in the face like a thug and it has been transfiguring.
Every few weeks my daughter and I stand back to back in the kitchen, socks off, our bare feet cooling on the tiled floor, and we measure up. I feel her body elongate itself at my back, straining upwards, squaring pre-teen shoulders against my sloping ones, while our bottoms, cushioned one against the other, are taut with tension. We look like a totem pole - bodies melded together, stony faces pointing outward, chins up and arms pressed against our sides. My husband circles us, bending his knees to get all the angles and squinting like a surveyor. "Not quite there yet," he says. "There's about two inches in it." Later he confesses to being spooked. "Looking at the two of you is like witnessing time travel," he tells me.
My daughter, who initiated this household ritual, has already dispensed with one yardstick: just before she turned 12, she overtook my mother. In her stride now, she is visibly delighted to be gaining on me. Standing on tiptoe and flinging an arm round my shoulder, she tries out equality and likes it. Soon enough there'll be no need for any artificial elevation. We will be peers, in the matter of height if nothing else.
My husband has already lost his way with the laundry. My daughter's knickers, candy-striped and tartan-checked, regularly turn up in my drawers, while my tights have begun disappearing into hers. She appropriates them, naturally, and wears them in the new style: opaque legs in black or navy under cut-off denim shorts. All the girls dress this way, come rain or shine, their toenails poking holes into their mothers' tights.
I've begun to see his category errors as a way of re-drawing the boundaries of our parenting duties. Having shared the job with me in a genuinely egalitarian, straight-down-the-middle fashion for the first 12 years of our daughter's life, he now, however unconsciously, seems to feel that our concerns fork into he-matters and she-matters. Underwear has become my domain, in consequence of which he need not task himself in thinking too hard about it. My own need to recalibrate my relationship to our daughter is just as pressing. But it is of a different order.
Every mother meets the paradox that the more their daughters are drawn into womanhood the more they pull away.
It is a confusing social induction that appears to obey strange magnetic rules: daughters are attracted to the adult world of women, but repelled by their actual mothers. Their resistance is primal, and fundamentally self-protective: for how is a girl to acquire a distinct sense of her identity when every pubescent change her body undergoes threatens to blend her into a confusing melange with the woman who birthed her?
It is little wonder the father-daughter bond is often so strong - which is another thing mothers must contend with. In my household, watching Star Trek re-runs and end-to-end episodes of The Simpsons are both folies a deux: as are American pancake feasts, not caring that the dog stinks, loafing in baggy T-shirts, confecting newfangled desserts late at night, ice-skating, planning camping trips that never happen, and more.
I'd be lying if I said I didn't mind being excluded, even if this all sets a reassuringly high bar for the men who may come into my daughter's life later. But I take her affinity for difference to be largely unavoidable. If a daughter is to properly separate from her mother, then it stands to reason that she will cement that opposition by forging closer ties with her father.
What complicates matters further is my own need to detach from her. This is a developmental issue, particularly poignant for women in midlife, and seldom given proper attention.
If my daughter and I tussle, it is because each of us, not just her, is striving to find her own ground; I, to sever myself from the young woman I once was, and of whom she so strongly reminds me: she, from a tyrannous feeling that she's a mini-me - not just a doppelganger, but her mother-in-training.
At the cusp of adolescence, she is changing in ways that feel peculiar and unexpected - flesh filling out nascent curves, thick hairs sprouting wilfully. With her bio-rhythms synched to a wayward chemistry, she's become moody, lippy and incredibly self-conscious (privacy is now permanently manifested with a capital P).
A smart girl, she's grasped that the source of her discomfort is the oddity of standing with one foot in childhood and the other in proto-adulthood. Her instinct is to hold firm to the ground she knows. While her classmates experiment with makeup and teenage posturing, she seems reluctant to put away childish things. It is as if she's intuited that these next months will be her last hurrah when it comes to Minecraft, Sylvanians, secret spy books and a lingering affection for the scantily clad, super-power fairies of the cartoon franchise Winx Club.
I've never felt us to be more mirrored. In middle age, my body is also changing in surprising ways: my skin is crepey, my joints click and pop. While her hormones rage, mine are plummeting.
She's discovered sleep; I'm suddenly insomniac. Her memory is a fine-tuned thing; mine is perpetually tripping up. At the same time, both of us ricochet between crankiness and euphoria.
As if this were not upheaval enough, to my great irritation I am once again prone to glaring outbursts of acne, just as she breaks out in spots. After decades of feeling comfortable in my skin I, too, am now deeply self-conscious.
Not surprisingly, ours is a household of fireworks; one of us, my daughter or me, can always be relied upon to ignite the other's latent combustibility.
At the opposite end of the reproductive spectrum, I am acutely aware of the threshold at which my daughter stands today. I want to wave at her in sympathy and recognition and assure her it will turn out well. I want to tell her that on the other side of this difficult adolescent transition there will be freedoms and experiences she's never dreamed of, as well as new heights of confidence and competence. There will be deep friendships and deeper loves, the roller coaster of university life and first jobs, independent travel, opportunities at every turn. I want to tell her that her dreams will become tangible. That her fears will drift into obscurity.
That she will feel invincible.
But then I am overcome by a terrible sadness for my own lost opportunities, and by an ersatz nostalgia for paths not taken - a missing, if you like, of what I never had, and a misplaced anxiety about all the future paths I shall never take because with middle age comes a shrinking sense of the possible. Since half of me is lost in undifferentiated yearning for what might have been (and never will be), I am often unable to reassure my daughter with the right level of conviction. If I am to succeed in this task, I must first let go of my ghostly younger selves, not least the ones who can floor me, which is the grown-up version of putting away childish things.
There is a roadmap for much of our lives, neatly plotted out. In simplistic guise it goes something like this: your teens are for studying, your 20s for experiments and fun; in your 30s you consolidate (careers, relationships, finances) and start parenting; then in your 40s you acquire stature and kind of peak; and in your 50s, the horizon I am now looking towards, the lucky few get to peak again, while others experience middle age as a kind of mugging, robbing them of a feeling that the future might actually hold more than the past.
This conventional, and admittedly First World, blueprint is no better than any other prescribed path. In fact, it strikes me that those who hew most closely to its contours in youth end up feeling most lost in middle age. Where that leaves me in terms of counselling my daughter through adolescence is not entirely clear. But I wish to encourage her to embrace The Unknown. After all, with every step you take into the murk the fog recedes a little.
What I can tell my daughter is that the world of unknowns before her is not so frightening as she thinks. Or, more accurately, it is less frightening than it is limiting - every road chosen, a path not taken.
In the best of my idealised scenarios, she and I journey into the unknown together as our mirroring continues. She departs from the blueprint as much as she likes, learning and adventuring by turn, while I venture into my foggy 50s, one air-clearing month at a time.
Edited extract from The Middlepause by Marina Benjamin (Published monday. Scribe, $30).