"It only takes one drink to for your boyfriend to cheat on you," said a nurse at the West Virginia University student health center. As funny as that sounds, infidelity is the age-old plague that kills most relationships and marriages. According to an iVillage survey, approximately 1 in 5 adults have cheated on their partner. There has always been a stigma towards cheating, but why does it happen? Is cheating a part of biological instinct? Or is it just an impetuous cheap thrill that happens in the moment? Are some people genetically predisposed to cheat?