Whether you're generous like the patriarch Abraham or a cheapskate like Scrooge may be the result of your genetic makeup rather than your upbringing or your adult environment, according to a team of Hebrew University researchers. Dr. Ariel Knafo of the Jerusalem university's psychology department and his colleagues believe that those inclined toward generosity are genetically programmed to behave that way. The researchers posed an on-line task in which participants had to decide whether or not to give virtual money away, and found that those who chose to give away some or all of their money differed genetically from those who were tightfisted. There were 203 on-line "players" - each of whom could choose to keep the equivalent of $12 or give all or part of it to an anonymous other player. Those involved also provided DNA samples, which were analyzed and compared to their reactions. It was found that those who had certain variants of a gene called AVPR1a gave an average of nearly 50 percent more money than those not displaying that genetic variant. The results of the study were published on-line recently in the research journal Genes, Brain and Behavior. "The experiment provided the first evidence, to my knowledge, for a relationship between DNA variability and real human altruism," said Knafo, who conducted the research along with other researchers, including Prof. Richard Ebstein (discoverer of the "risk-taking gene"), Prof. Gary Bornstein and Salomon Israel of the HU psychology department. The gene AVPR1a codes for the production of a receptor that enables a hormone, arginine vasopressin, to act on brain cells. Vasopressin, in turn, has been found to be involved in social bonding. The researchers found greater altruism in players in which a key section of the AVPR1a gene (called its "promoter") was longer. The promoter is the region of a gene that allows cellular machinery to bind to it and determine how much gene product is made. In the case of this gene, a longer promoter can result in greater activity. The findings could help biologists sort out altruism's evolutionary history, according to the scientists. They noted that a version of AVPR1a also exists in rodents called voles, where it also promotes social bonding. This suggests that altruism has a deep-rooted genetic history, which may have taken on a new role during human evolution.