I would like to show a little story. A story of how life might have evolved on this planet we call home.
This story may seem not have anything to say about consciousness and its role, but it does in an important context of the definition of consciousness: awareness of one's environment (of one's self comes later as full sentience). The modern analogs to the prototypes have unique features that relate to the idea of consciousness. These features are sensitivity to light and the cytoskeleton.
To explain, photosensitivity evolved in a hostile environment in which the atmosphere of the ancient Earth had no ozone layer to protect life from the ionizing effects of ultraviolet radiation. But the same life still depended upon the use of the energy of the Sun to survive (along with the use of geothermal energy of volcanic vents). So, a compromise resulted: a cell would float in just the right depth of water that allowed for light to penetrate to aside metabolism but not too shallow otherwise it would be killed and not too deep or it would starve to death. Simply put, this mechanism allowed even a simple single celled organism to be aware of its environment and to behave in a complex manner unlike its prototype ancestors as shown in the demonstration video link. In fact, the very genes related to photosensitivity are found in the majority of life on the planet and as a result is the basis of eye sight in every animal on Earth. A simple adaptation with no nervous system, no neurons, and no memory allowed for a cell to behave intelligently.
Another example is the cytoskeleton. This structure is unique in the fact that its obvious role is to support the weight and shape of a cell's wall. But what is not obvious is two other features. First, its role as a 'highway' of sorts for molecules in the cell, which allow for more efficient and fast use of molecules in the life cycle of a cell. Second, the natural composition of such a cytoskeleton results in the same behavior found in carbon nanotubes: conductivity. What this second feature of the cytoskeleton results in the ability of a cell to 'know' where its being touched by another cell or natural barrier in the environment. That means a cell which could be equiped with a flagella could know exactly what side of its is being touched and where to go as to not be touched (as to not be eaten/killed). This particular feature of the cytoskeleton results in another hint or clue as to the nature of consciousness; that it is partly a reactionary function of a living thing.
But this story gets more complex as you begin to move through natural history to animals. You will begin to find animals that develop the ability to have memory as speciation doesn't result often enough to make 'better' (more efficient) adaptations for a given species or set of species to survive in its environment. Memory could be classed as an adaptation, but I would hazard against such a classification because the addition of any complexity in an organism means that organism has to sustain the costs of that complexity whether times are fat or thin. A simple nervous system can still be a metabolic cost that is too high for some niches and as a result it's obvious why it has taken as long as it has for it to appear.
Furthermore, when one progresses through natural history even further to our times one begins to see lifeforms with brains similar to modern ones which have the ability to sort memories and adjust them. These brains appear simple, but in contrast to an animal with a simple nervous system its features are a magnitude greater in complexity. But now move even further forward in natural history and look at the different species that evolve even more to use these brains for other purposes: socialization. The ability to develop hierarchy in a social group for an animal is quite advantageous as it allows for a division of labor not seen as evident until modern industrialization. Whether it's the primates (humans), canines (wolves), or some other class of animal one can see that socialization in groups and the development of hiearchy allowed for these animals to survive better with less resources in a single area.
Ultimately, this is when the very concept of self-awareness or self-consciousness begins to appear and the very story that started with very simple chemistry and physics allows for the emergence of the ability to self-shape/determine. The point is that consciousness is an emergent property that exists in parallel to evolution as neither evolution nor consciousness seem to have any common ground beyond the accidental advantages resulting from consciousness in its orders of magnitude of utility for a given species. At the same time it can be said that consciousness is inevitable for all life forms at least in terms of adaptation, but I can't hazard that as the majority of the biomass of all life on Earth is outweighed by the single celled organisms by a wide margin. Thus, I don't believe in any sort of bio-determinism for consciousness.
