What is consciousness?
The question of consciousness (and of 'I') stays at the core of philosophical thought since the times of Descartes; however, if expressed as the quest on soul, it is one of the oldest problems intriguing the human reflection.
Though Descartes had already taken into consideration some material-neural connotations, the term is still generally wrapped in spirituality, as is revealed by many verbal expressions used even by those who declare themselves as supporters of a materialistic conception. Inside the spiritual domain, however, positions are quite varied, from the old idea of an entity responsible for all perceptions, thoughts and actions, to the opposite views confining consciousness to the role of a simple, ineffective spectator, and even suggesting that it could be entirely absent, this fact being in no way detectable by an external observer (zombie hypothesis).
However, it is possible to report about consciousness in verbal and written terms, and specific criteria exist which recognize its occurrence. This supports a physical-neural nature and implies the existence of a neurally coded definition, liable in principle to be thoroughly described verbally.
In spite of the large variety of conceptions about the type and importance of consciousness involvement, the rich lists of the functions in which it is claimed to be interested - perception, abstract thought, affects, emotions, volition - largely coincide.
Quite likely, consciousness began when many of the above functions already existed and were well structured; consequently, its development occurred mostly in parallel with those neural chains of causation. This collateral involvement allowed a large modulation of conscious interventions, from a mere monitoring to a role of control and coordination, up to a predominant and decisive steering: thus, noticeably, covering the range of proposed consciousness involvements considered above.
Organized in this way, conscious control is expected to be conformed in detail to the various, pre-existing functions. This contrasts with the conception of consciousness as a totipotent, undifferentiated entity, emerging when a certain level of complexity has been exceeded - similar to the spontaneous generation of living beings, claimed by researchers who considered life as a powerful, ultramaterial, unitary force, and not the ipercomplex machinery which has revealed to be. Thus, complexity appears to be a necessary conditions, but not a sufficient one.
It should be noted that, if consciousness is the result of an adaptive development along evolution, probably it has not reached a final state yet, and, if it occurs in more than a single animal species, its features may differ from case to case.