Political scientists are keenly interested in how diversity influences politics, yet we know little about how diverse groups of political actors interact. We advance a unified theory of colleague valuation to address this puzzle. The theory explains how minority group size affects how members of a political organization differentially value majority and minority group colleagues, predicting that the effect of preference divergence on individual-level colleague valuation is greatest when the minority group is smallest. We test this prediction using member-to-member leadership political action committee (PAC) contributions in the U.S. House of Representatives. The results obtain strong, albeit not uniform, support for the theory, demonstrating that the gender gap in colleague valuations declines as preference divergence increases in all but one instance. In contrast to conventional wisdom, the theory and evidence indicate that women serving in the U.S. House of Representatives receive less support from men colleagues as their ranks increase.