Many people think that by walking the spiritual path, our consciousness evolves.
But in yoga, changes occur in brain biology, not in consciousness. Spiritual progress through yoga is the result of changes in the biology of the brain and nervous system. The state of the brain and body will determine if any living organism will be able to tune into different dimensions of consciousness or not.
Reptiles have a primitive nervous system, which has helped them survive. The reptilian complex in the human brain is representative of the brain of reptiles and is a mirror for reptilian consciousness. In advanced animals, the brain is responsible for emotions. And in humans, the brain has brought the wonders of self-awareness, through which we are able to experience feelings and emotions. It also gives us the ability to reflect on the past and contemplate the future. We are capable of logical thinking, which has unleashed endless creativity and has led to the emergence of science, art, ethics, religion and culture.
But above all of this, is the incredible ability we possess to feel the presence of the infinite and eternal, the source of the universe itself. The infinite is not an empty void — but contains all that is possible, was possible and will be possible. People have given this feeling of boundless and timeless existence many names, including God, Brahma and so on.
As our brain develops and vibrates at a particular frequency, we experience a specific level of consciousness. The animal brain vibrates at a different frequency than in humans, and so their perception is different. Because we are self-aware, we can change the structure and physiology of our brain, and then become more conscious of those experiences that are not available to other living beings. This is conscious evolution.
Yoga is the science of conscious evolution. Evolution is essentially the evolution of the brain, which can vibrate at different frequencies at various stages of evolution.
Like yoga, all creative and spiritual practices are about changing the structure and physiology of the brain, in order to tune into a more conscious experience. We have the potential to become conscious of every evolutionary frequency, eventually arriving at a point where the frequency becomes infinite. It is here where the pure consciousness of enlightenment (Samadhi) is experienced.
A normal brain, though fully active physiologically, does not typically function at optimal capacity because various parts of the brain remain remain unconnected. But in yogic awakening, not only do some of the physiologically less active parts of the brain become more active, but more parts connect to allow the brain and nervous system to function as one whole.
So really, it's the brain that evolves, not the consciousness. We practice yoga to allow the brain to evolve, so that we can become receptive to higher levels of consciousness which are actually available to us all the time.