The Pill may also have changed women's taste in men, according to a study.
Scientists say the hormones in the oral contraceptive suppress a woman's interest in masculine men and make boyish men more attractive. Although the change occurs for just a few days each month, it may have been highly influential since use of the Pill began more than 40 years ago.
If the theory is right, it could partly explain the shifting in tastes from macho 1950s and 1960s stars such as Kirk Douglas and Sean Connery to the more wimpy, androgynous stars of today, such as Johnny Depp and Russell Brand.
Dr Alexandra Alvergne, of the University of Sheffield, says the Pill could also be altering the way women pick their mates and could have long-term implications for society.
Scientists have long known that a woman's taste in men changes over her menstrual cycle.
During the few days each month when women are fertile - around the time of ovulation - they tend to prefer masculine features and men who are more assertive.
On days when women are not fertile, their tastes swing towards more feminine, boyish faces and more caring personalities, researchers have shown.
However, if women are taking the Pill they no longer have fertile days. That means they no longer experience the hormonal changes that make them more attracted to masculine men and those with dissimilar genetic make-up.
Or maybe the dearth of manly men can be laid to something in the water.
When EPA-funded scientists at the University of Colorado studied fish in a pristine mountain stream known as Boulder Creek two years ago, they were shocked. Randomly netting 123 trout and other fish downstream from the city’s sewer plant, they found that 101 were female, 12 were male, and 10 were strange “intersex” fish with male and female features.
It’s “the first thing that I’ve seen as a scientist that really scared me,” said then 59-year-old University of Colorado biologist John Woodling, speaking to the Denver Post in 2005.
They studied the fish and decided the main culprits were estrogens and other steroid hormones from birth control pills and patches, excreted in urine into the city’s sewage system and then into the creek.
Woodling, University of Colorado physiology professor David Norris, and their EPA-study team were among the first scientists in the country to learn that a slurry of hormones, antibiotics, caffeine and steroids is coursing down the nation’s waterways, threatening fish and contaminating drinking water.