"THE FINDING that an environmental toxin can permanently reprogram a heritable trait also may alter our concept of evolutionary biology. Traditional evolutionary theory maintains that the environment is primarily a backdrop on which selection takes place, and that differences between individuals arise from random mutations in the DNA. The work by Skinner and his group raises the possibility that environmental factors may play a much larger role in evolution than has been realized before."
—From a June 2, 2005 news release from Washington State University describing research by Michael Skinner and colleagues, whose recent paper in the journal Science described how exposing pregnant rats to environmental toxins altered the male offspring's fertility and sperm counts—as well as those of males in every generation therafter. The cause appears to be "epigenetic inheritance," in which chemical modifications to genes—including modifications induced by environmental toxins—can permanently alter the way the genes work.