Nature vs. Nurture

While my wife and I were visiting our family in central Florida, we went to Sonny's for one of our lunches in order to satisfy our barbecue hunger. When we went inside, I held the door for my wife and my mother-in-law. As another family came behind us, I remained at the door, holding it open for this other family. I had never met them before. Then, something unexpected happened. A young man of the family, who was perhaps 16 or 17 years old, offered to hold the door for me and let me go ahead of him. At this, my stubbornness surfaced, and I stayed my post, insisting that he go ahead as I was already here. He responded that he would be more than happy to take my place. After a short friendly exchange, he entered while I followed behind. My family sat down, not really sure of what was said between the young man and I. They did not know at first that we were conversing about who should be holding the door for whom. As we finished our meal and made our way to the front so that we might pay for our meal and leave, the young man excused himself from his own meal, slipped in front of us, and remained at the door, holding it until we all had passed through it. Then, he returned to finish the rest of his lunch. Such an encounter makes me smile as it gives me hope that virtue is not dead.
I give the previous story so that I might ask the question, what motivated this young man to battle with me over courtesy? Was it how he was raised (nurture)? or was it based upon his genetic makeup (nature)? I remember being intrigued by this oft-debated topic when I was enrolled in Introduction to Psychology. This question is presented, yet no satisfying answer seems prevalent, at least no answer that I find satisfying. Something seems to be lacking, namely freedom.
When one asks the question of nature versus nurture, the discussion is already set. Namely, the question assumes determinism with the goal of finding what is the particular determinant.
The primary means of asserting accountability for one's actions (which Christianity certainly does by claiming that God is judge and will reckon to all what he or she is due) seems to be the positing of libertarian free will. This notion of free will holds that nothing outside of an individual determines what actions that he or she will take. While some finer points can be made (such as some decision do determine what is possible thereafter), at least one decision in life will be freely made (at this point, I would recommend Ken Keathley's Salvation and Sovereignty).
One way to substantiate this claim is to reflect upon the fact that I have desires, Yet, just because I desire to do something does not mean that I will do something. Furthermore, just because I know something does not necessitate that I will act on that knowledge (such would be the case of a heart doctor that will not pass by fried chicken and mashed potatoes with gravy). The way the world is remains distinct from the way the world ought to be.
Perhaps the world would be a much different place should people consider themselves responsible for the situations they find themselves in and for their reactions to those situations. rather than seeking someone or something else to bear the blame.