“Emotional contagion is deeply rooted in our evolutionary past,” says study co-author Nicholas A. Christakis, MD, PhD, MPH, a physician and sociologist at Yale University (previously of Harvard). “One can think of emotions as a primitive form of communication: it is of use to me to notice, and copy, your fear, disgust, anger, or happiness.” MORE: How Failure Leads To Happiness (Seriously) A study published last year in PLoS ONE showed that you can pick up someone’s joy just by watching someone else watching the happy person (like a happiness middleman!), meaning our moods can affect people we don’t even know—and theirs ours, and without our awareness. A joy transfer can take place even if you’re not physically near the person: a new study that Christakis co-authored in 2014 found that emotions also spread among friends on Facebook. “When people make a positive change in their lives by being or acting happy or optimistic, they not only benefit themselves but many others,” Christakis says. “And those others are generally people they care about—that is, I can help myself and the people I care about by being happy.” MORE: How To Be Happy…Even If You’re Not Exactly An Optimist
