Inherited Pollution

All of these changes took place without any changes in the rats' DNA code.

Chemical tags can attach to DNA and act like "stop signs" to turn genes off.

"This is one of the first transgenerational effects of an environmental toxicant identified," Skinner wrote, "and the first indication that epigenetic mechanisms can permanently alter the germ-line and genetic traits of all subsequent generations and progeny of an exposed individual."

"It's not just about male infertility," says Skinner.

It's also not just about environmental toxins. As reported in Discover magazine, the fact that epigenetic changes can be both permanent and inherited without altering the DNA code explains a host of mysteries. "It's a mechanism in which the animal can respond to the environment, and you can literally pass that information on to the next generation," says Duke University's Randy Jirtle.

Jirtle led the groundbreaking experiments in which a slight tweak to the diet of genetically identical mice resulted in wildly different offspring in both appearance and health. Giving pregnant mice dietary supplements including folic acid caused their offspring to be brown and lean rather than yellow-coated and obese. The yellow obese mice had all the health risks we associate with obesity, including diabetes and heart disease, and the changes were passed on to subsequent generations.

Jirtle points out that theoretically any environmental factor could have epigenetic effects. "People who take drugs, be it alcohol or illicit drugs as mothers when they're pregnant -- versus ones that don't -- those potentially would have effects that we're talking about right now in mice."

Jirtle's experiments found that feeding different diets to genetically identical mice results in wildly different offspring.

"We're not simply the products of a combination of mom and dad's genes," says collaborator Frances Champagne of Columbia University. "We're a product of lots of different factors, including the experiences our mom and dad had, and the experiences we had."

While the new discoveries may spawn many new concerns, researchers say it also means we have more control than we thought over what we pass on to our descendents, as well as throwing open new doors to disease treatments.

"What if it’s not a DNA sequence mutation event that causes many diseases to develop, but it’s truly the epigenetic background of the individual that determines whether they are going to be susceptible or develop the disease?" asks Sklinner. "If that’s the case, then we have a whole host of new diagnostics and therapeutic targets which we didn’t have before."

Indeed, Jirtle suspects that epigenetic inheritance may be behind some of the toughest diseases to crack, such as autism, bipolar disorder and schizophrenia.

"The argument of whether it's nature or nurture is starting to totally disappear as a concept any more," Jirtle says. "Even nurture is working through genes."

Skinner and others published their two new papers in Endocrinology, September 14, 2006. Skinner's research is funded by the National Institute for Environmental Health Sciences (NIH). Jirtle's research is funded by the National Institutes of Health (NIH) and the Dannon Institute fellowship. Champagne and Meany's research is funded by the National Institutes of Mental Health (NIH) and the Canadian Institutes for Health Research.