Development of ethics can be drawn for a number of sources:
Laws, which punish bad behavior.
Religion/philosophy, which provides a set of principals and governing moral code.
Ethical Relativism, which states that ethics are determined by social norms.
Conscience, an internal moral compass.
I believe the primary source of ethics are individual integrity and personal responsibilities from our life experiences. We develop our ethics as soon as we learn how our actions impact others. Our ethics evolve and truly take shape when we are presented with difficult situations, life-changing events, and complex decisions. If you tell yourself you believe something is right or wrong but are not able to follow through when your convictions are tested, your true ethics are being decided in those moments.