A prevailing view considers the self a property of only the most evolutionarily advanced animals. We propose that a “protoself’ is already present in simple life forms and may be an inherent aspect of all living systems. A separation of the “self” from the “outside” world allows organisms to model the external environment and to act on it. The appearance of the nervous system in larger organisms, initially necessary for speed, enabled the generation of more sophisticated models of the environment and the organism that could be harnessed for more accurate predictions of the future. Spontaneous neuronal activity, such as the default mode network which is prevalent in humans, may serve as an integrator of the model, physically implementing the self as an emergent property.