Organizational ecology is commonly seen as a Darwinian research program that seeks to explain the diversity of organizational structures, properties and behaviors as the product of selection in past social environments in a similar manner as evolutionary biology seeks to explain the forms, properties and behaviors of organisms as consequences of selection in past natural environments. We argue that this explanatory strategy does not succeed because organizational ecology theory lacks an evolutionary mechanism that could be identified as the principal cause of organizational diversity. The "evolution" of organizational populations by means of selection, which organizational ecologists put forward as the mechanism responsible for the extant diversity of organizational forms, is not evolution in any proper sense, because organizational populations do not have what it takes to participate in evolutionary processes. This implies that organizational ecology is not a Darwinian research program and that it cannot explain organizational diversity. © 2009 SAGE Publications.