Organizational collaboration is "en vogue", especially in higher education. So far, little is known about the mechanisms that explain co-operation formation and their impact on the social structure of the research systems. By examining co-authored research papers written at South African universities between 1966 and 2006, co-operation structures are visualized and analyzed from a social network perspective. Regression analysis indicates that status homophily and geographical proximity help to explain attachment processes among universities. Policy makers looking to overcome the steep status hierarchies among South African institutions of higher education need to provide incentives for establishing a stronger research culture in previously disadvantaged institutions. This will enhance their attractiveness for co-operation with reputable organizations and contribute to more equality among institutions.