They were easy to find. They came willingly. Some of them even refused to be reimbursed for travel expenses. And none of that should have surprised researchers. After all, to qualify for the study being run by Georgetown neuroscientists you had to have donated a kidney to a stranger. So what did the research suggest? These extreme altruists have bigger brains and are more sensitive to the facial expressions of others. The researchers believe their findings support “the hypothesis that our ability to care about the plight of others falls within a spectrum,” with extreme altruists on one end and psychopaths (and web commenters) on the other.

+ Is there a simple blood test that can diagnose depression and predict who will be most receptive to therapy?