Kindness begets kindness, according to science:

Goodness spurs goodness: A single act can influence dozens more.

In a game where selfishness made more sense than cooperation, acts of giving were “tripled over the course of the experiment by other subjects who are directly or indirectly influenced to contribute more,” wrote political scientist James Fowler of the University of California, San Diego, and medical sociologist Nicholas Christakis of Harvard University.

Their findings, published March 8 in the Proceedings of the National Academy of Sciences, are the latest in a series of studies the pair have conducted on the spread of behaviors through social networks.

In other papers, they’ve described the spread of obesity, loneliness, happiness and smoking. But there was no way to know whether those apparent behavioral contagions were actually just correlations. People who are overweight, for example, might simply tend to befriend other overweight people, or live in an area where high-fat, low-nutrient diets are the norm.

According to the the researchers, "the explanation lies not in calculations of odds and rewards, but in simple behavioral mimicry: Monkey see, monkey do, human style. When people are irrationally generous, others follow suit."

Nice.

Like yawning.