What helps a species survive? “Most people assume that in order to thrive, you’ve got to be big and mean,” says Vanessa Woods, an anthropologist at Duke University in North Carolina. But she and a colleague have a different theory. For many animals, fitness—the ability to survive and reproduce—comes down to friendship and cooperation. Dogs, for example, are successful because of their close bond with humans. The concept extends to people too. Being friendly toward those who are different from you is good for collaborating and exchanging different points of view, explains Woods. “Learn from dogs,” she says. “Wag more. Bark less.”