But all cells respond to stimuli.
Why do I bring this up here? Because we, as humans, are not "hard-wired". Sure, we are born with genetic materials that define the color of our hair and eyes and other primary characteristics. But from the moment we are conceived, we are constantly adapting to the imposed demands of our world - in utero, and in the world as we know it.
And our central nervous system - that which makes us who we are - undergoes those same types of adaptations.
We are on the planet as dynamic entities. Our bodies virtually recreate themselves as new cells develop and old cells die. Each day is a little different than the one before, and each new day brings new stressors - physical, mental, emotional, spiritual - that challenge us to adapt. We make the best choices we can given whatever we have to work with at any given point in time. We evolve. If we aren't evolving, the species is dying.
And if the species is dying, this is all a moot point anyways.
Remember that every day, you are a slightly different person than the day previous - not to make you feel schizophrenic, but to simply be cognizant that growth and adaptation are in a constant state of flux. Life is dynamic, and change is good. Go forth - and evolve. Today.