However, as theory surrounding social networks has developed, sociologists such as Alejandro Portes and the Wisconsin model of sociological research began placing increased leverage on the importance of these weak ties. While strong ties are necessary for providing residents with primary services and a sense of community, weak ties bring together elements of different cultural and economic landscapes in solving problems affecting a great number of individuals. As theorist Eric Oliver notes, neighborhoods with vast social networks are also those that most commonly rely on heterogeneous support in problem solving, and are also the most politically active.