Before we can begin to consider the evolution of consciousness, we have to ask when consciousness first arose. Are human beings alone conscious, or are other creatures also conscious? Is an animal such as a dog, for example, conscious?
Dogs may not be aware of many of the things we are aware of. They are not conscious of much beyond their immediate world, the world defined by the span of their senses. They know nothing of lands beyond the oceans, or the space beyond the earth. Nor can dogs be aware of much beyond the present time.
They know nothing of the course of history, or where it might be headed. They are not aware of their inevitable death in the same way that we are. They do not think to themselves in words, and they probably do not reason as we do. And they do not seem to have the self-awareness that we do; they certainly do not get caught up in concern for their own self-image, with all the strange behaviors that engenders. But this does not mean that dogs have no awareness at all.
Dogs experience the world of their senses. They see, hear, smell, and taste their world. They remember where they have been. They recognize sounds. They may like some people or things, and dislike others. Dogs sometimes show fear, and at other times excitement. When asleep, they appear to dream, feet and toes twitching as if on the scent of some fantasy rabbit. They clearly are not just a biological mechanism, devoid of any inner experience. To suggest that they are not conscious is absurd — as absurd as suggesting that my neighbor across the street is not conscious.
Where dogs differ from us is not in their capacity for consciousness but in what they are conscious of. Dogs may not be self-aware, and may not think or reason as we do. In these respects they are less aware than we are. On the other hand, dogs can hear higher frequencies of sound than we do, and their sense of smell far surpasses our own. In terms of their sensory perception of the world around, dogs may be considered more aware than humans.
A useful analogy for understanding the nature of consciousness is that of a painting. The picture itself corresponds to the contents of consciousness; the canvas on which it is painted corresponds to the faculty of consciousness. An infinite variety of pictures can be painted on the canvas; but whatever the pictures, they all share the fact that they are painted on a canvas. Without the canvas there would be no painting.