Oh my bad...
I
thought you meant moral consciousness.
To answer for this, we would need to first define consciousness.
"Consciousness is a quality of the mind generally regarded to
comprise qualities such as subjectivity, self-awareness, sentience,
sapience, and the ability to perceive the relationship between
oneself and one's environment."(Wikied)
Most atheists would agree that consciousness is not unique in
humans. Dolphins and other high-level animals also displayed
consciousness.
This can be explained using scientific approach. Every emotion,
feeling and thought process that we experience, are but a series of
complex electrical signals handled by our brain, not just the
pineal gland.
Take for example the corpus callosum (communicating bridge between
two cerebral hemispheres). If you cut it, the 2 brains will not be
able to communicate with each other. They will not be able to
receive perceptive signals from either sides of the body. This
effectively creates '2 consciousness' , if you will, in the same
physical body.
Then again, neurology is still pretty much at it's infantile stage
and is very underdeveloped. Being no subject matter expert, this is
the best explanation I can offer you now.