Man, Aristotle said, is by nature a social animal. This is the premise of Tina Rosenberg’s new and important book, “Join the Club,” which examines the idea that human behavior is defined by our relationships with our acquaintances. Peer pressure, she finds, can lead to acts of great courage, or to great harm. But Rosenberg’s particular ambition is to unlock the secret of using it to “transform the world,” in the words of her subtitle. Calling this approach the “social cure,” she examines how social networks can address some of the world’s most recalcitrant problems — from adolescent cigarette smoking to despotism.

In tracking the social cure, Rosenberg draws upon her career as a Pulitzer Prize-winning journalist who has studied the sources of human courage (she chronicled Chile’s democratic revolution) as well as the sources of human suffering (she’s visited many of the world’s most impoverished and disease-stricken places for The New York Times Magazine and other publications). Her new book takes the reader to the democratic revolutions in Serbia, Georgia and Ukraine, the H.I.V./AIDS-racked communities of South Africa, the villages of India and Bangladesh, and even the suburbs of Chicago where members of a megachurch struggle to forge social bonds. She combines her on-the-ground reportage with cleareyed accounts of recent findings in social psychology, neuroscience, sociology, public health and a gamut of other fields. By the end of the book, the reader has circled the globe and the social sciences several times over.

Human beings interact in several different ways — in the marketplace, in the struggle for political power and as peers in the community. Our market relations are dominated by the quest for profit and consumer satisfaction; our political relations are dominated by the competition for power; and our peer relations are dominated by the search for status, identity and acceptance by others. Rosenberg argues that the third kind of relationship, the search for status and peer approval, is the most powerful motivator of our personal behavior and that it can be employed to remedy social ills. She calls on us to “reimagine social change . . . based on the most powerful of human motivations: our longing for connection with one another.”

Her examples are often impressive. In Jamkhed, an impoverished district in western India, the training of women to become community health workers broke down the normally high barriers between Indian castes. The low-caste women, Rosenberg notes, “acquire their new self-image in part through their new role in the village, the satisfaction of helping their neighbors and the respect they have earned from the villagers. As a result of the knowledge and skills of the Jamkhed women, the villages change.”