Before long, strange couples were being found all round the United States from the Pacific north-west to Massachusetts. When the reluctant males were caught and examined the story became stranger still. For they were found to have grown female egg-laying canals.
Or perhaps we will fix on the inadequate alligators. In the late 1980s, scientists trying to find out why few of the reptiles' eggs were hatching at Lake Apopka in Florida found that more than half the males had mysteriously tiny penises. Further research revealed that they had female hormone patterns - and that turtles in the same lake had developed into hermaphrodites.
Then again, it could be that the warning was really sounded by the Danes. In 1990, experts at Copenhagen University began to wonder why sperm banks were finding it so hard to build up a register of donors. Only one out of every 10 volunteers was producing enough of the stuff to qualify. When they investigated they found that average sperm counts in Denmark and in 19 other countries all over the world had been cut by half in the previous 50 years. There is no sign that the decline has stopped there.
Growing alarm at these bizarre developments - and many more of the same - will be focused next week on the British publication of a disturbing new book. Our Stolen Future (Little Brown, pounds 18.99), which became an overnight sensation when it was issued in the United States last month, ascribes these and a host of other disorders to a range of man-made substances.
These substances are now found all over the Earth, from Antarctic sediments to the breast milk of Inuit in the Canadian Arctic, and everywhere in between. They are used in children's toys and beer bottle caps, in pesticides and shoes, in upholstery and rocket fuel. And they contaminate much of what we eat and drink.
In the foreword, Vice-President Al Gore repeatedly compares the book to Rachel Carson's classic Silent Spring which 30 years ago aroused the world to the dangers of pesticides. He calls it "a critically important book that forces us to ask new questions about the synthetic chemicals that we have spread across this Earth" and adds: "Initial animal and human studies link these chemicals to myriad effects including low sperm counts, infertility, genital deformities, human cancers, neurological disorders in children, and developmental and reproductive problems in wildlife."
The prestigious US National Academy of Sciences has set up a special panel to assess the threat and the Administration's Environmental Protection Agency has identified the substances as a top research priority, fearing they could become "a very serious problem". It is also introducing new rules for testing chemicals for their effects on reproduction.
Here in Britain, the Chemical Industries Association guardedly agrees that "there is enough evidence to suggest cause for concern", while the Ministry of Agriculture - already in disarray over the BSE crisis - is preparing itself for another outcry.
The book describes the plummeting sperm counts as "the most dramatic and troubling sign" that the pollution may already have had a major effect. A team led by Niels Skakkebak of Copenhagen University concluded, after examining 61 separate studies covering more than 15,000 men on all five continents, that the average count has fallen from 113 sperm per millilitre of semen in 1940 to 66 million in 1990.
Some scientists dispute his findings, but more and more are coming to similar conclusions. Most recently, the Medical Research Council reported that the fertility of Scottish men born since 1970 was 25 per cent less than those born in the 1950s, and that sperm counts were declining by about 2 per cent per year.
Pierre Janouet, a French reproductive biologist who first attacked Skakkebak's work, and then confirmed it through his own research, has said that, at the present rate of decline in the count "it will take 70 or 80 years before it goes to zero".
Theo Colborn, a tall, spare, 69-year-old grandmother, makes an unlikely scientific prophet of doom, yet it is her research that has linked the gay gulls, the inadequate alligators and countless other disturbing natural phenomena with falling sperm counts and other human disorders. Our Stolen Future is based on her work and she is one of its three authors - with Dianne Dumanoski, a Boston Globe journalist, and John Peterson Myers, the head of a US environmental foundation.
A pharmacist and the widow of a Colorado farmer, she decided, at 51, to go back to college because she wanted to "get out from behind the drugstore counter, dishing pills". Armed with a PhD, she ended up nine years ago at Washington's Conservation Foundation, researching the effects of pollution in the Great Lakes. Fish in the lakes had been found to develop cancer and she was trying to find out whether the contamination was causing the disease in people too.
Her results at first seemed reassuring. There was no sign of higher rates of cancer in the area than elsewhere in the US. But, during her research, she had turned up study after study showing reproductive failure, population declines, behavioural changes and disease in 16 species ranging from eagles to salmon, otters to terns, gulls to turtles. She set out the data on a giant computer spreadsheet.
As she scanned the screen, three common factors stood out. First, all of the most affected species were - like humans - at the top of food chains. Persistent pollutants, which accumulate in fat, build up as each predator eats many prey: thus a herring gull concentrates them 25 million times over.
Second, mainly young creatures were affected; adult ones were relatively unscathed. And third, Dr Colborn's pharmacological background told her, most of the cases could be linked to disruption of the endocrine system, which she calls the "biological equivalent of the information superhighway".
The endocrine system carries messages that govern sex and reproduction, regulate behaviour and immune systems, and co-ordinate organs and tissues that work together to keep the body functioning. Hormones play an extremely important part in this process, particularly in the unborn child. They are quite extraordinarily powerful, having effects at concentrations of parts per trillion, the equivalent of one drop of gin in 660 railway tanker trucks of tonic.
There is increasing evidence that some chemicals act, as the book puts it, as "thugs" on the highway, "sabotaging vital communication". It adds: "They mug the hormone messengers or impersonate them. They jam signals. They scramble messages. They sow disinformation. They wreak all manner of havoc."
Working from more than 12,000 scientific papers from around the world, Dr Colborn says that at least 51 man-made chemicals have been identified as "hormone disrupters", and that at least half of them are persistently building up in body fat. Some mimic the female hormone, oestrogen. Others block the male hormone, testosterone. Still others break down and eliminate a wide variety of them.
The best attested is DES, a synthetic chemical designed precisely to imitate oestrogen, long given to pregnant women to try to prevent miscarriages. Babies exposed to it in the womb have grown up with reproductive defects, and the girls are at higher risk of getting vaginal cancer.
But most of the hormone-disrupting chemicals have taken scientists by surprise, and some are very common. Use of the pesticide DDT was once almost universal, and is still widespread in developing countries. It mimics oestrogen and breaks down into chemicals that attack hormones.
Nearly one and a half million tons of the extremely persistent PCBs have also been spread around the world - in a host of uses, from paints to pesticides, plastics to electrical equipment. Several studies report that infertile men have higher levels of them than normal.
Dioxins, some of the most toxic of known chemicals, also disrupt hormones: male rats exposed to only a single small dose in the womb have dramatically reduced sperm counts. Several thousand tons of just one herbicide containing them was used every year in the 1970s, to keep down weeds and brush on railway lines, fields and lawns.
Dioxins, DDT and PCBs all accumulate in body fat. When a mother breast- feeds, the book points out, she passes on chemicals long stored in her fat to her child. It calculates that every day a breast-feeding North American or European baby will receive five times the allowable level of PCBs for adults. But there are so many benefits to babies from breast- feeding that the authors draw back from discouraging it.
Nowhere is uncontaminated. Some of the most remote places are among the most affected by persistent chemicals, because these are concentrated enormously in food chains on their way there - three million times over, for example, in the fat of an Arctic polar bear.
Dioxins, PCBs and DDTs have all been tightly regulated or banned for years in many countries, but still persist in the environment and in people. And they are now being joined by new classes of chemicals, also thought to disrupt hormones.
In 1987 Dr Ana Soto of Tufts Medical School in Boston inspected some scientific plates where she was growing breast cancer cells with differing levels of oestrogen. To her amazement she found the cells were proliferating, even when none of the hormone had been added. Pain-staking detective work established that an oestrogen- mimicking chemical, nonylphenol - added to polystyrene and PVC to make them less breakable - was leaching from the plastic used in the test tubes.
This was the first sign that plastics previously thought to be inert may also be contributing to hormone disruption and falling sperm counts. It was also found that another plastic, polycarbonate - used in bottling spring water - similarly leached an oestrogen-mimicking chemical.
Concern is growing too over phthalates, used in PVC and a wide range of other plastics to make them more flexible, though these are little mentioned in the book. Some 2.7 million tons of them are produced world- wide each year. They have been found as far away as in Antarctic sediments and in the air over the great oceans and are thought, says Greenpeace, to be the world's "most abundant environmental contaminants".
Ministry of Agriculture research has found phthalates inBritish food, from meat to sweets, ice lollies to pasta, dried fruits to cheese - either because they were there originally, or because they have leached into them from wrappings. It accepts that phthalates are "ubiquitous" and can cause reproductive effects in mammals, but says there are "unlikely to be health risks".
Theo Colborn and her colleagues are not just worried about falling sperm counts and other reproductive changes. They point to evidence linking hormone-disrupting chemicals to breast, testicle and prostate cancers, to endometriosis (a common cause of female infertility), and to damage to the immune system. But they are most anxious about increasing evidence that the substances damage the brain in the womb and in early life, causing hyperactivity and aggression. Studies have shown these effects in children exposed to PCBs before birth - maybe as many as one in every 20 in America.
"By disrupting hormones and development," say the authors of Our Stolen Future, "these synthetic chemicals may be changing who we become. There may be fates worse than extinction."
Nothing is proven. In fact most of the possible damage to humans would be impossible to prove. Because they cannot be subjected to laboratory experiments, there is no way of knowing what doses each person has received, and there are no uncontaminated people on Earth to provide a comparison.
The book has already provoked furious argument in the US. The chemical industry points out that humanity has long been exposed to natural oestrogen- mimicking chemicals in many cereals, vegetables and fruits, without suffering any apparent harm. The authors reply that the species has had time to evolve resistance to these natural sources, but not to the synthetic ones and that imitating oestrogen is only one of the new substances' tricks. They cite strong evidence of damage to animals in laboratory experiments, and point out that these are particularly significant as the endocrine systems of mammals are remarkably similar.
Already authorities are beginning to react. PVC water bottles have been banned in Switzerland, Sweden plans to phase out the plastic, and councils all over Europe have started taking precautions. The Chemical Industries Association promises that it will "immediately take steps", including possible bans, "if research evidence concludes that specific chemicals are causing human reproductive health problems". Al Gore may be right: this week's publication could turn out to be the most significant since Silent Spring.