If you’re a person of a certain age, it’s likely that the house you grew up in was much smaller than the one you have today. And the car your family drove then–generally one per household–was a third the size of the one you drive today. How do social mores and expectations change over time? Psychologists for a long time have understood that we influence one another much more strongly than most people realize. Economist Robert H. Frank, of Cornell University, and author of ‘Under the Influence’ seizes on this concept to suggest that behavioral contagion can be harnessed to affect positive societal change. If you think about recent successful movements, whether it’s The Tea Party or #MeToo, can you name a leader in either case? With social media and the rapid transmission of new ideas, things that seemed implausible moments earlier can happen rapidly. Two other momentous examples, in recent history, were the fall of the Berlin Wall ending the Cold War and the rapid adoption of same sex marriage as the law of the land. The concept of behavorial contagion is a powerful one. The effect our friends and neighbors have on our own behavior places social influence in a whole new light. Just consider the example of solar panels going up in your neighborhood. Listen in to find out what we mean.