Something very strange is happening in a small but highly polluted Canadian community. And it may explain why every year thousands of British babies who should be boys are born as girls instead.
Young boys are becoming hard to find on the Chippewa Indian reservation in the gritty town of Sarnia, in Ontario's "Chemical Valley". It boasts four children's softball teams, but three of them are made up entirely of girls.
Research shows that the number of boys being born to the community has been dropping precipitously for the past 13 years, while the proportion of baby girls has risen. Now there are twice as many female births as male ones, though nature normally keeps the sexes in balance.
Scientists increasingly believe that pollution is to blame and that what has happened here - and among some other highly contaminated groups of people in other countries - may solve an enduring mystery of "missing boys" in maternity units throughout the industrialised world.
Normally, and with remarkable consistency around the globe, 106 boys are born for every 100 girls; the excess is thought to be nature's way of compensating for the fact that males were more likely to be killed through hunting and conflicts.
But this figure has been slowly declining in rich countries over the past quarter of a century. In Britain it has fallen to about 105 since 1977 -which suggests that every year more than 3,000 babies are born as girls instead boys. Studies have revealed much the same story in the US, Canada, the Netherlands and the Scandinavian countries.
Suggested explanations have included increasing stress and rising numbers of single mothers; women in difficulties, it has been found, produce more girls than boys. But what is happening in Sarnia, on the US Canadian border, is increasingly turning the spotlight on pollution.
The Chippewa Indians of the Aamjiwnaang First Nation Community have long lived in the area, on the southern tip of Lake Huron, not far from Detroit. Their right to the land was confirmed in 1827, but much of it was taken over by industry in the 1960s.
Now their woods and homes are entirely surrounded by one of the world's most extensive petrochemical complexes, producing 40 per cent of Canada's entire output of plastics, synthetic rubber and other chemical compounds. The air stinks, and the ground is contaminated with high levels of dangerous pollutants.
It was those softball teams that first got the 870 people of the community thinking that many more girls than boys were being born. Among them was Ada Lockridge, a 42-year-old home help aide, who sits on the community's council. She and her sister had eight daughters between them, and only one son.
She started counting all the babies born to the community since 1984, Until 1993 girls and boys were in normal balance, but then the number of male births started plummeting. "I felt like I wanted to throw up," she says. "I did a lot of crying. And then I got angry."
She joined up with researchers from the University of Ottawa and together they published an article in a leading scientific journal. It reported "a significant ongoing decrease in the number of male births beginning in the early 1990s".
Only 35 per cent of babies now are boys, and there is no sign of the decline levelling off. The study could not prove a cause, but pointed the finger at "multiple chemical exposures over the years".
Other, non-native communities downwind of the complex also have less dramatic reductions in male births, while those upwind do not. And many studies have shown sex changes in fish and wildlife in the lake nearby.
Ada Lockridge points to a fire and chemical release at one of the chemical plants in 1993 as a possible culprit.
The findings tally with other research around the world. People exposed to high levels of dioxin in the 1976 accident in Seveso, Italy, also have twice as many girl as boy children. The same is true for Russian men exposed to pesticides containing the chemical.
And Brazilian scientists have reported that the proportion of boy babies fell in the most polluted parts of the city of São Paulo.
Professor Shanna Swan of the University of Ro chester, New York - not far from Sarnia - says that levels of contamination on the reservation are "incredible" and that the "first assumption" must be that they are to blame. She believes that changing sex ratios may often provide an indication of dangerous pollution, and that low levels of exposure to such ubiquitous chemicals as dioxins and PCBs may explain the decline in boys in industrialised countries.
Additional reporting by Martin Mittelstaedt in OntarioReuse content