Both genetics and the environment they were raised in (morals, etc.) contribute to the person and their character. Some things are genetic and there is little one can do to overcome those things (nature) while other things are learned and can be changed if one works hard enough (nurture), depending on which personality traits you are speaking about will determine which is true. For example, both my parents have bad tempers, naturally so do I, however I have worked hard at proper ways to channel my anger so I don't react in inappropriate ways. Hope that helps.