The hypothesis of the origin of consciousness is built upon the unique properties of the mammalian neocortex. The apical dendrites of the pyramidal cells bundle together as they ascend to lamina I to form neural receptor units of approximately 100 apical dendrites plus branches receiving hundreds of thousands of excitatory synapses, the collective assemblage being called a dendron. It is proposed that the whole world of consciousness, the mental world, is microgranular, with mental units called psychons, and that in mind-brain interaction one psychon is linked to one dendron through quantum physics. The hypothesis is that in mammalian evolution dendrons evolved for more effective integration of the increased complexity of sensory inputs. These evolved dendrons had the capacity for interacting with psychons that came to exist, so forming the mental world and giving the mammal conscious experiences. In Darwinian evolution, consciousness would have occurred initially some 200 million years ago in relation to the primitive cerebral cortices of evolving mammals. It would give global experiences of a surrounding world for guiding behavior beyond what is given by the unconscious operation of sensory cortical areas per se. So conscious experiences would give mammals evolutionary advantage over the reptiles, which lack a neocortex giving consciousness. The Wulst of the avian brain needs further investigation to discover how it could give birds the consciousness that they seem to have.