This chapter defines mind as a subdomain and internalized posting of the psychological and makes it a specific and defining feature of the mammal. It is argued that mind as a faculty of emotion, memory, and representation, and anchored in the limbic system, has evolved from REM sleep in the early evolution of the mammalian brain. The name-giving feature of the mammal is the breast-feeding of its off-spring, and it is described how this reproductive mode is the end-result of an evolutionary trend from a quantitative reproductive strategy (safety in numbers) to a qualitative (safety in extended care). Finally it is described how the unique mammalian features form a complex and place the mammals in their own distinctive life-world.