The important bit, to me, is: Most people are conditional reciprocators; the more money you send them, the more they tend to send back. About 2 percent of our t

The important bit, to me, is: Most people are conditional reciprocators; the more money you send them, the more they tend to send back. About 2 percent of our test subjects were non-reciprocators. Oxytocin typically has an off/on sequence. It's released within seconds in response to a social cue, and then production switches off again. But in about 2 percent of my subjects, the ones who never cooperated, their brains appear not to be turning off their oxytocin production. They are way off the curve for their peripheral oxytocin levels. In addition, they don't seem to respond to oxytocin like other subjects, who reciprocate more strongly the more oxytocin they have. This suggests, although it doesn't prove, that they have a dysfunction in the oxytocin receptors -- the wrong location or inhibited binding -- that causes them to behave like "bastards."