The nature versus nurture debate just took an unexpected turn -- thanks to pollution.
Increased exposure to the toxic chemical mercury can affect sexual preference in certain species of birds -- inducing homosexuality, a new study has revealed.
Peter Frederick, an ecologist from the University of Florida, and Nilmini Jayasena from the University of Peradeniya in Sri Lanka found that male American white ibises that consumed methylmercury, the most toxic and easily digested form of mercury found in the environment, were more likely to pair with other males. In wild ibis populations with no mercury exposure, same-sex pairing is non-existent.
"We knew that mercury was likely to affect reproductive hormones from an earlier study," Frederick told FoxNews.com, "so we suspected some aspect of reproduction would be affected, like whether the birds came into reproductive condition or whether they were too aggressive to pair."
"We had no clue that mate choice might be involved," he added.
Birds living in wetlands, such as the ibises, are most vulnerable because the environment is a breeding ground for bacteria that convert the mercury spewed from coal-fired power plants into methylmercury, which "is at least ten times as toxic as the stuff in a thermometer," Frederick said.
Mercury becomes methylated only when it comes in contact with bacteria in anoxic environments, those that use sulfur instead of oxygen for metabolism. And that process is common in wetlands and shallow aquatic areas, Frederick said.
"The implication is that this is probably happening in wild bird populations," Frederick told Nature magazine.
Frederick and Jayasena studied 160 white ibis nestlings over a three-year period. They found that males with higher levels of mercury were less likely to be approached by females and had a higher chance of being involved in a homosexual pairing. As the level of mercury exposure increased, so did the degree and persistence of homosexual pairing.
Frederick believes that the methylmercury, a known endocrine disruptor, is affecting hormone levels in exposed birds.
While the team hopes their findings sheds light on the effects of mercury pollution, Frederick makes clear that people shouldn’t think that humans ingesting mercury will suddenly become gay. "I want to be very explicit that this study has nothing to say about that," he told Nature.
That said, mercury pollution is a danger to humans for a variety of other reasons: It's known to affect developing fetuses and has degenerative effects on many human organs.
"There are numerous reasons why cleaning up the environment for birds also reduces risk for humans," Frederick said.
The results of the study are published in the current issue of Royal Society B.