We propose consideration of at least two possible evolutionary paths for the emergence of intelligent life with the potential for technical civilization. The first is the path via encephalization of homeothermic animals; the second is the path to swarm intelligence of so-called superorganisms, in particular the social insects. The path to each appears to be facilitated by environmental change: homeothermic animals by decreased climatic temperature and for swarm intelligence by increased oxygen levels.
Schwartzman, David and Middendorf, George, "Multiple Paths to Encephalization and Technical Civilizations" (2011). Department of Biology Faculty Publications. 229.