Consciousness developed very slowly.  The first glimmer is found in the lowest molecules, in their ability to interact with, to respond to, their environment.  Whitehead and Teilhard are on the right track in this regard.  (Leibniz is not.)

I had to look again at these thinkers to see what God was getting at.  Rejecting the mind-nature dualism, the twentieth-century philosopher-mathematician Alfred North Whitehead held that, even at the micro level, every event is a pulse of existence, feeling and responding to its environment.  These “prehensions” are not so much states as vectors, arrows pointing to connections with the surrounding world.  The Jesuit scientist-philosopher Pierre Teilhard de Chardin spoke of the “within” of things, their interiority, which “appears at the heart of beings”:  “Co-extensive with their Without, there is a Within to things.”  In every part of the universe, “the exterior world must inevitably be lined at every point with an interior one.”  By contrast, the seventeenth century philosopher-mathematician G.W. Leibniz believed that everything in the universe was made of elementary particles that were not matter or energy, but minds, centers of consciousness, each of which internally mirrors all the others.  In short, Whitehead and Teilhard believed that physical (or psycho-physical) nature has levels of awareness—and they were on the right track—whereas Leibniz held that there is no physical nature other than points of consciousness.

As God went on, He sounded a lot like Teilhard.

What happens is that reactions have an internal dimension—responding to the environment, the molecule begins rearranging its internal parts and configurations and processes.  This is the beginning of interiority.  Ultimately, interiority involves the second-order process of monitoring and directing inner processes.  But, even at the beginning, prior to the emergence of second-order processes, there is an emerging consciousness.  To be conscious is not the same as and does not require self-consciousness.  It can be very dim and limited and still be consciousness, because something new and remarkable has arisen—the pre-sentient and then sentient awareness of the environment.  Don’t worry at this point about what is meant by “pre-sentient” awareness.  Your understanding is necessarily anthropocentric, using human consciousness as the standard by which to understand all forms of consciousness.