Word: eggs
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Dates: during 1990-1999
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Couched in a halo of nutrient cells, an egg smaller than the dot on an i drifts slowly down a Fallopian tube, one of a pair of narrow passages that lead from a woman's ovaries to her womb. Like a beacon guiding ships at night, the egg sends forth a calling signal. A convoy of sperm -- the remnants of an armada that was once a couple of hundred million strong -- sails into view, their long tails thrashing vigorously. Lured by the chemical signal, several hundred of the most energetic swimmers close in on the egg, their narrow tips unleashing...
...only one succeeds. The instant it tunnels its way past the egg's outer layer, an electric charge fires across the membrane and a signal from the sperm causes the eggshell to snap shut, blocking entry to any remaining contenders. The successful seed then releases its tightly coiled package of DNA, which fuses with the egg's own DNA and sets in motion a series of genetic events that culminate, nine months later, in the birth of a new human being...
...what if it doesn't work? What if egg meets sperm and nothing happens? Human sexual reproduction, as couples even before Sarah and Abraham have known, can be a heartbreakingly unreliable process. Even under the best of circumstances -- a fertile couple having intercourse at the optimum moment in the woman's cycle -- it fails 3 times out of 4. When conditions are less than ideal -- when the woman is over 35, for example, or the man's sperm is defective or in short supply -- the odds lengthen dramatically...
...remarkable advances, scientists have opened a new window on the mysteries of fertilization that shows for the first time not only how the process works but also what can be done when it doesn't. Doctors today can manipulate virtually every aspect of the reproductive cycle, from artificially ripening eggs in the ovary to inserting individual sperm directly into the egg's inner membrane. Now researchers at several U.S. clinics are pushing the scientific envelope even further, screening embryos for genetic defects in the lab before placing them in their mothers' wombs...
...techniques have also given birth to once unimaginable ethical dilemmas. Do sperm and egg donors have a claim on their biological offspring, and vice versa? Do embryos, frozen or thawed, have a constitutional right to life? How much manipulation of genetic material will society be willing to permit? "Technology makes us look at our most cherished conceptions of who we are and what we want to be," says Dr. Kenneth Ryan, a professor of reproductive biology at Harvard Medical School. "People have to decide what kind of society they want to live...