Researchers say boys aren't as tough as they used to be.
Not in the womb, at least.
A special report in today's Journal of the American Medical Association finds that the number of male births is down significantly" in the USA, Canada and other nations.
The report suggests environmental factors may play a role because at the same time there's been a rise in the frequency of defects in male sex organs. That leads the authors to think some males died before birth and other fetuses that would have developed into boys became girls.
The default gender is female," says Michelle Gottlieb, a report author and a researcher at the World Resources Institute, a Washington-based policy research group. Males tend to be extremely sensitive to environmental exposure or disruptions of the hormonal development in the womb."
Researchers compared birthrates over 20 years with the world average of 106 boys for every 100 girls, which makes 51.5% of newborns boys.
In the USA, that rate fell from 51.34% in 1970 to 51.21% in 1990. The result: Over the 20-year period, 38,000 fewer boys were born than expected.
Canada's 20-year loss was 2.2 males per 1,000 births, or 8,600 fewer males. Similar declines were noted in the Netherlands, Scandinavia, Finland and Germany.
The study was launched after a 1976 explosion at a Seveso, Italy, chemical plant. Later, researchers saw twice as many girls as would have been expected born to families that were exposed to a pesticide.
Gottlieb says the new findings could be like the canary in the coal mine," indicating chemical exposure hazards.
Robert Mittendorf of the University of Chicago says that drawing such conclusions about pollutants is a stretch."
Gottlieb wants more study.
We're not sure exactly, biologically, what's going on," she says. But there is a trend here, and it deserves more attention. The cause may not be benign."
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