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GLOBE EDITORIALS
New evidence about eggsAMONG THE SETTLED truths in biology, one that has long seemed beyond challenge is that women are born with all the eggs they will ever have. Men, on the other hand, keep producing sperm right to the end. Now this gender difference has been thrown in doubt by Massachusetts General Hospital researchers who have found strong evidence that in mice, at least, stem cells in the ovaries keep producing new eggs long after birth.
Scientists are a long way from proving this in human females, and if it is proved, it will be longer yet before new fertility treatments develop from the work of Dr. Jonathan L. Tilly and his MGH team. Another study last week raises doubts that extending women's fertility is necessarily a good thing for the species. Evidence that female mammals' bodies do not create new eggs after birth has always been circumstantial. Examinations of cadavers of different species turned up counts of eggs that declined with age. The higher frequency of Down syndrome in babies born to older women compared with younger women has been attributed to abnormalities that occur in eggs as they age in the ovaries. But what if it isn't eggs themselves that are getting older but stem cells in the ovaries that produce them, and continue to produce them well into a female's middle years? The MGH work already has scientists discussing the possibility of extending stem cell productivity and delaying menopause. Still, a study by Finnish and Canadian researchers suggests that the extended period between menopause and death might have an important place in nature's plan. Scientists have been puzzled by this relatively long period in the lives of women between menopause -- when they can no longer help in reproducing the species -- and death. The Finnish and Canadian study discovered an evolutionary purpose to a woman's golden years: She can help in raising extra grandchildren. An examination of records in 18th- and 19th-century Finland and Quebec shows that for every decade a woman lived beyond the age of 50, her line included two extra grandchildren. The researchers found that this was true even in pre-industrial times, so the long postmenopausal stage of women's lives is an "evolved phenomenon" and not just a reflection of the better nutrition and health care of modern life. The aid that the grandmothers provide is hands-on: The data showed that children living farther than 12 miles from their mothers produced significantly fewer children than those who lived in the same village. This "grandmother hypothesis" suggests that any additional children women might bear by delaying menopause could be offset by fewer grandchildren. For most 55-year-old women, that's an easy choice. © Copyright 2004 Globe Newspaper Company.
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