Woman: An Intimate Geography (5 page)

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resulting embryo in said senior's uterus. Using donor eggs can make a woman of forty act like a twenty-five-year-old, reproductively speaking. Who knows why? But it works, oh girl does it work, so well that suddenly you're no longer in the teens of probability but instead have about a 49 percent chance of giving birth in a single cycle of in vitro maneuvers. That number starts to sound like a real baby bawling. If the wine is young enough, it seems, the bottle and its label be damned.

And so the egg rules the roost. It, not the womb, sets the terms of tomorrow. Carol-Ann Cook takes one of Derochea's eggs and puts it under a high-powered microscope, which transmits the image to a video monitor. "This is a beautiful egg," Bustillo says. "All her eggs are beautiful," Cook adds. They are eggs from a healthy young woman. They have no choice but to shine.

To think of the egg, think of the heavens, and of weather. The body of the egg is the sun; it is as round and as magisterial as the sun. It is the only spherical cell in the body. Other cells may be shaped like cinched-in boxes or drops of ink or doughnuts that don't quite form a hole in the middle, but the egg is a geometer's dream. The form makes sense: a sphere is among the most stable shapes in nature. If you want to protect your most sacred heirlooms your genes bury them in spherical treasure chests. Like pearls, eggs last for decades and they're hard to crush, and when they're solicited for fertilization, they travel jauntily down the fallopian tube.

Carol-Ann Cook points out the details of the egg. Surrounding the great globe that glows silver-white on the screen is a smear of what looks like whipped cream, or the fluffy white clouds found in every child's sketch of a sky. This is in fact called the cumulus, for its resemblance to a cloud. The cumulus is a matting of sticky extracellular material that serves to bind the egg to the next celestial feature, the corona radiata. Like the corona of the sun, the corona of the egg is a luminous halo that extends out a considerable distance from the central orb. It is a crown fit for a queen, its spikes and phalanges emphasizing the unerring sphericity of the egg. The corona radiata is a dense network of interlocking cells called nurse cells, because they nurse and protect the egg, and it may also act as a kind of flight path or platform for sperm, steering the rather bumbling little flagellates toward the outer coat of the egg. That thick, extracellular coat is the famed zona

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pellucida the translucent zone the closest thing a mammalian egg has to a shell. The zona pellucida is a thick matrix of sugar and protein that is as cunning as a magnetic field. It invites sperm to explore its contours, but then it repels what doesn't suit it. It decides who is friend and who is alien. The zona pellucida can be considered the mother lode of biodiversity, the place where speciation in nature often begins, for it takes only a minor change in the structure of its sugars to make incompatible what before was connubial. The genes of a chimpanzee, for example, are more than 99 percent identical to ours, and it is possible that if the DNA of a chimpanzee sperm cell were injected directly into the heart of a human egg, the artificial hybridization would produce a viable, if ethically repulsive, embryo. But under the natural constraints of sexual reproduction, a chimpanzee sperm could not breach the forbidding zona pellucida of a human egg.

The zona also thwarts the entry of more than one sperm of its own kind. Before fertilization, its sugars are open and genial and seeking similar sugars on the head of a sperm. Once the zona has attached to the head of a sperm, it imbibes the sperm, and then it stiffens, almost literally. Its sugars turn inward. The egg is sated; it wants no more DNA. Any sperm that remain at its threshold soon will die. Still, the zona's task is not through. It is thick and strong, an anorak, and it protects the tentative new embryo during the slow descent down the fallopian tube and into the uterus. Only when the embryo is capable of attaching to the uterine wall, a week or so after fertilization, does the zona pellucida burst apart and allow the embryo to join its blood with mother blood.

The corona, cumulus, and zona all are extracellular, auxiliaries to the egg but not the egg. The egg proper is the true sun, the light of life, and I say this without exaggeration. The egg is rare in the body and rare in its power. No other cell has the capacity to create the new, to begin with a complement of genes and build an entire being from it. I said earlier that the mammalian egg is not like a bird's egg, insofar as it lacks the nutrients to sustain embryonic development. A mammalian embryo must tether itself to the mother's circulatory system and be fed through the placenta. But from a genetic perspective, the cytoplasm of a mammalian egg is complete, a self-contained universe. Somewhere in its custardy cytoplasm are factors proteins, or bits of nucleic acid that allow a genome to stir itself to purpose, to speak every word its

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species has ever spoken. These maternal factors have not yet been identified, but their skills have been showcased in sensational ways. When Scottish scientists announced in 1997 that they had cloned an adult sheep and named her Dolly, the world erupted with babble about human clones and human drones and God deposed. The endless exercises in handwringing resolved very little of the ethical dilemma that surrounds the prospect of human cloning, if dilemma there be. But what the sweet ovine face of Dolly demonstrates without equivocation is the wonder of the egg. The egg made the clone. In the experiments, the scientists extracted a cell from the udder of an adult sheep, and they removed the nucleus from the cell, the nucleus being the storehouse of the cell's genes. They wanted those adult genes, and they could have taken them from any organ. Every cell in an animal's body has the same set of genes in it. What distinguishes an udder cell from a pancreatic cell from a skin cell is which of those tens of thousands of genes are active and which are silenced.

The egg is democratic. It gives all genes a voice. And so the scientists harvested a sheep egg cell and enucleated it, taking the egg's genes away and leaving behind only the egg body, the cytoplasm, the nonyolk yolk. In place of the egg nucleus they installed the nucleus of the udder cell, and then they implanted the odd chimera, the manufactured minotaur, into the womb of another sheep. The egg body resurrected the entire adult genome. It wiped the slate clean, washed the milky stains from the dedicated udder cell, and made its old genes new again. Maternal factors in the egg body allowed the genome to recapitulate the mad glory of gestation to recreate all organs, all tissue types, the sum of sheep.

The egg alone of the body's cells can effect the whole. If you put a liver cell or a pancreatic cell into a uterus, no infant would grow of it. It has the genes to make a new being, but it has not the wit. Small wonder, then, that the egg is such a large cell. It must hold the secrets of genesis. And perhaps the molecular complexity of the egg explains why we can't produce new eggs in adulthood, why we are born with all the eggs we will ever have, when men can sprout new sperm throughout their lives. Scientists often make much of the contrast between egg and sperm, the prolificacy and renewability of the man's gametes compared to the limitations and degradative quality of a woman's eggs. They speak in

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breathless terms of sperm production. "Every time a man's heart beats, he makes a thousand sperm!" Ralph Brinster burbled to the
Washington Post
in May of 1996. But a woman is born with all the eggs she'll ever have, he continued, and they only senesce from there. Yet the mere ability to replicate is hardly cause for a standing ovation. Bacteria will double their number every twenty minutes. Many cancer cells can divide in a dish for years after their founder tumors have killed the patient. Perhaps eggs are like neurons, which also are not replenished in adulthood: they know too much. Eggs must plan the party. Sperm only need to show up wearing top hat and tails, of course.

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2
The Mosaic Imagination: Understanding the ''Female" Chromosome

Keith and Adele fought all the time, like a pair of tomcats, like two drunken lumberjacks. Keith would find grist for the arguments in his reading. He read widely and thirstily, and sometimes he would come across a stray fact that fed his theorizing about the natural cosmology of male and female. Males are the seekers, he had decided, the strugglers and the creators; they build all that we see around us, the artifactual world of towering cities and invented divinity, yet they suffer for their brilliance and busyness. Females are the stabilizers, the salve for man's impatient expansionism, the mortar between bricks. Nothing surprising there: it's a familiar dialectic, between the doers and the be-ers, the seethers and the soothers, complexity and simplicity.

Then one day Keith read about chromosomes. He read that humans have twenty-three pairs of chromosomes and that the pairs of chromosomes are the same in men and in women, with the exception of pair number 23 the sex chromosomes. In that case, women have two X chromosomes and men have one X and one Y. Moreover, a woman's two X chromosomes look pretty much like all her other chromosomes. Chromosomes resemble Xs. Not when they're inside the cells of the body, at which point they're so squashed and snarled together they resemble nothing so much as a hair knot. But when they're taken out of the cell and combed apart for viewing under a microscope by a geneticist or a lab technician who is checking a fetus's chromosomes as part of amniocentesis, they look like fat and floppy Xs. So women have twenty-three pairs, or forty-six, of these X-shaped structures, while men have forty-five Xs and that one eccentric, the Y chromosome. The Y physically resembles the letter it was named for, being stubby and

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tripartite and quite distinct in shape from all the other chromosomes in the cell.

It struck Keith that even on a microscopic level, even as inscribed in the genetic clay from which human beings are constructed, men demonstrate their edge over women. Women have as their sex chromosomes two Xs: monotony. The story we've heard before. Men have an X and a Y: diversity. Genetic innovation and an escape from primal tedium. The Y as synecdoche for creativity for genius. And so he said to Adele, The chromosomes prove the case for male superiority. You have two Xs and hence are dull, while I have an X and a Y and am accordingly interesting.

Neither Adele nor Keith knew much about genetics, but Adele knew enough to recognize mental manure when she smelled it. She dismissed his theory with a sneer. He grew angry at her refusal to submit to his logic. The argument escalated, as their arguments always did. Keith wasn't talking about all men, of course, but about himself. He was insisting that his needs and insights took precedence over Adele's, and that she acknowledge as much. She refused to surrender.

Of the many arguments that my parents had in the theater of our apartment before the reluctant audience of their children, this is the only one whose substance I remember. The clash of the century, Y versus X. I remember it in part because it seemed so oddly theoretical, and because it was the first time I heard an argument put forth for all-around, across-the-board male dominance. I took it personally. My feelings were hurt. It was one thing for my father to attack my mother that I was accustomed to. But there he was, describing all females, including me, as chromosomal bores.

The chromosome case remains very much open, a source of irritation and debate. In some ways, sex is fundamentally determined by the sex chromosomes. If you're female, you're assumed to have a pair of Xs tucked into just about every cell of your body, along with a set of those twenty-two other pairs of chromosomes. If you're a male, you know of your Y and you just might be proud of it, as your molecular phallus, and for the koanic wordplay of it: Y? Why? Why? Y! The sex chromosomes tell a technician and you the parent, if you choose to know whether the fetus under scrutiny in an amniocentesis screen is a girl or a boy.

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So in one sense the demarcation between X and Y is clear, clean, an inarguable separation between femaleness and maleness. And my father was right about the predictability and monochromaticity of the female chromosomal complement. Not only will you find two X chromosomes in every body cell of a woman, from the cells that line the fallopian tubes to the cells in the liver and brain, but break open an egg cell and look within the nucleus, and you'll find one X chromosome in each (again with the other twenty-two chromosomes). It is indeed the sperm cell that can add diversity to an embryo, and that determines the embryo's sex by delivering either another X, to create a female, or a Y chromosome, to make a male. X marks the egg. An egg never has a Y chromosome within it. An ejaculate of sperm is bisexual, offering a more or less equal number of female and male whip-tailed sperm, but eggs are inherently female. So in thinking again about the mirrors into infinity, the link between mother and daughter, the nesting of eggs within woman within eggs, we can go a step further and see the continuity of the chromosomes. No maleness tints any part of us gals, no, not a molar drop or quantum.
^*

But of course it is not that simple. We are not that simple, appealing though the idea of a molecularly untainted matriline may be. Let us consider the nature of the sex chromosomes, the X counterpoised against the Y. To begin with, the X is bigger, much, much bigger, both in sheer size and in density of information. The X chromosome is in fact one of the largest of the twenty-three chromosomes that humans cart around, and is about six times larger than the Y, which is among the tiniest of the lot (and it would be the smallest of all if it didn't have some nonfunctional stuffing added to it just to keep it stable). Gentlemen, I'm afraid it's true: size does make a difference.

In addition, many more genes are strung along the female chromosome than along its counterpart, and it is as a shoetree for genes that a chromosome takes on its meaning. Nobody knows exactly how many genes sit on either the X or the Y chromosome; nobody yet knows how many genes, in total, a human being has. Estimates range from 68,000


^*This system of sex determination by the male gamete is a mammalian phenomenon. Among birds, the opposite method holds true: the female has two different sex chromosomes, an X and a W, and it is her egg, not her mate's sperm, that determines the sex of the chick.

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