bad smaritan

Is being a bystander is formed because of that person's morals and ethics or is it the nature of human? David Cash decided not to help out the girl despite being in the position to prevent the incident from happening, and I don't necessarily consider it's all because of his morals and ethics but it was his human nature that also contributed to his action. He left the scene to not put himself into trouble and be out of the picture; I consider this as the animal's crisis prevention ability, yet it was still selfish of him to commit such act. There are conversations where we consider human nature as our morals and ethics, but I think they differ and independent among each other, and it was the human nature side that came strong out of David Cash.