| Abstract |
Many types of complex networks that occur in nature, such as those from biochemistry, neurobiology, ecology, and engineering, exhibit some of the same, simple, network structural properties, that is, “network motifs”. Network motifs refer to recurring, significant patterns of interaction between sets of nodes, and they represent the basic, building blocks of graphs. We examine patterns of motifs in a set of social groups, including the networks of terrorists, nation state alliances, friendship, travel, advice, twitter, and legislative cosponsorship. Findings reveal several common network substructures. Reciprocity of directed ties occurs much more frequently than expected by chance, and approaches the maximum in most social networks. Closed, or transitive, triads are more frequent than in equivalent random graphs, but not in twitter or travel. The motifs of terrorist networks resemble more closely those of close ties, rather than those of isolated cells. Intriguing four node patterns emerge as well. Results suggest that motifs could be used to fill in missing group ties when information is incomplete and to predict network genre from limited information (close ties vs. hierarchy). Motifs also contain the seeds of dynamic change. Networks with high levels of triangulation, for example, would be predicted to close open triads in the future. |