As if men don't have enough excuse for infidelity, science is providing yet another. According to researches at the Karolinksa Institute in Sweden, there is a gene allele which can affect the production of a hormone called vasopressin. Vasopressin is known to positively influence monogamy. Men with more than two of the gene allele 334 "were twice as likely to have had a marital or relationship crisis in the last year compared with those who lacked the gene variant."
Via LA Times .