Dying to save a stranger is NOT a tribal thing and animals do not sacrifice themselves for other animals outside thier "kin".
All other humans are our kin. People do not willingly go into situations where death is imminent (or completely unavoidable) for strangers. But we also have a cultural thing where putting yourself in harm's way for the good of others is deemed heroic. In all cases the one at risk is getting something out of it. There are no completely unselfish acts.
Having something and not using it is a choice, but if a person was indeed born "without it" then it would be an anomally, a "birth defect".
This is inconsistent with your idea that an a creator being is installing this morality gene in us. Your new theory about birth defects suggests that the creator being can fail, or be thwarted in giving his creation something that is completely necessary for them to function in everyday life.