Consciousness and the brain: evolutionary aspects.

Self-reflective consciousness is distinguished from 'simple' awareness and from conscious awareness. Awareness is a fundamental property of living matter as it reacts to environmental stimuli. A hypothesis is advanced to account for the general phenomenon of decussation of nerve fibres in the central nervous system of vertebrates. This feature, the crossing over of nerve fibres to the opposite side of the brain, is interpreted as exemplifying the inherent caution of living forms. The evolution of increasing complexity of structure in spinal cord and brain is a prerequisite for increasing awareness of the environment and for increasing freedom from its constraints. Conscious awareness is manifested in living forms primarily when they are learning to respond either to new stimuli or to internal demands such as breathing and walking. The relegation of learnt activities to the realm of unconscious reflex allows for concentration on new and more complex responses, which leads to further freedom of action. The seeming simplicity of human thinking rests on the increasing complexity of the evolving brain and of appropriate responses learnt during phylogenetic development. The human brain and its thinking functions are basically trustworthy because they are rooted in biological evolution.