We tend to think of Level 1 as the early part of the brain, which we share with the animals, and Level 2 as the evolutionarily recent part of the brain that distinguishes us as human. But back in 1963, Ulric Neisser made the intriguing suggestion that it might be the sophistication of our unconscious processes that make us human: It is worth noting that, anatomically, the human cerebrum appears to be the sort of diffuse system in which multiple processes would be at home. In this respect it differs from the nervous system of lower animals. Our hypothesis leads us to the radical suggestion that the critical difference between the thinking of humans and of lower animals lies not in the existence of consciousness but in the capacity for complex processes outside of it.
Thus, it is not merely reason that separates us from the other animals, but the advanced nature of our emotions, especially our social and moral emotions.
The Social Animal: The Hidden Sources of Love, Character, and Achievement (David Brooks)