You might think your behaviors and opinions are totally unique to you. But you might be surprised to learn how much influence social networks exert. Scientists say our friends and our friends’ friends are often much more powerful than we think. Yale psychologist Laurie Santos has looked into why animals trust and follow information from others. And University of Pennsylvania psychologist Coren Apicella spent six months living with the Hadza, a hunter-gatherer community in east Africa. She studied how and why people choose the friends they do in the environment where our brains originally evolved.