It was the lawyers of ancient Rome who came up with the modern definition of fatherhood: Mater semper certa est; pater est quem nuptiae demonstrant . The Romans, however, didn’t have access to genetic testing. Dylan Davis did. A few months after his divorce in 2000, Davis, 36, a software engineer in Denver, took a DNA test to confirm a nagging suspicion that he was not the biological father of his 6-year-old twins. The negative test results led him to give up partial custody of the boy and girl–“The anger grows and grows, and it just keeps chipping away at your love for those children,” he says–and since his ex-wife moved to another state, he has had no contact with the twins. But under Colorado law, he is still required to pay $663 a month in child support. So Davis is lobbying to change the statute so that he and others like him won’t be held financially accountable for children who aren’t biologically theirs. Advocates for these so-called duped dads say such men should be treated as victims of fraud and liken the need for paternity-disestablishment amendments to truth-in-lending laws. They point to many an egregious case in which the law’s marital presumption of fatherhood has ended up enslaving a divorced dad, like the Michigan man who proved he had not sired his son but was still ordered to send child-support payments directly to the boy’s biological father, who was granted custody after the mom moved out of his place and left the kid there. Increasingly, policymakers across the country are turning a sympathetic ear to such complaints. Florida last year joined Georgia and Ohio in allowing a man to walk away from any financial obligations regardless of how many years he may have been acting as a minor’s father if he discovers he was deceived into parenthood. Fathers’ rights groups in Colorado, Illinois and West Virginia are pushing for similar legislation that would remove or extend existing time limits for challenging paternity. Spearheading the legislative movement is Carnell Smith, a Georgia engineer who found out shortly after he broke up with his girlfriend that she was pregnant and spent the next 11 years believing he was the girl’s father. Then, in 2000, after his visitation time had been cut back around the same time that a court order nearly doubled his monthly child-support payments, he took a test that showed he was not the biological parent. Three years and about $100,000 in child support and legal fees later, Smith, 46, managed to disentangle himself from any responsibilities for the girl, and says he walked out of court “a broke but free man.” He successfully lobbied his home state to pass its paternity-fraud law in 2002 and now runs a DNA-testing company. Its slogan: “If the genes don’t fit, you must acquit!” But justice for a disillusioned dad can clash with the best interests of a child raised to think of him as a father. “These cases get cast as the duped dad vs. the scheming wife,” says Temple University law professor Theresa Glennon, who has examined the changing legal landscape. “This is really about men deserting children they have been parenting.” She points out that severing paternal ties could devastate a child depending on the length and quality of his relationship with the nonbiological father.