It is now generally accepted that the roots of our ethics lie in patterns of behavior that evolved among our pre-human ancestors, the social mammals and that we retain within our biological nature elements of these evolved responses. We have learned considerably more about this responses, and we are beginning to to understand how they interact with our capacity to reason.
A choice is the root of all morality. Without choice, one can have no moral code. In a vacuum bereft of alternatives, there can be no values. And without values, there can be no reason for a code of ethics. What gives our lives meaning is which alternatives we choose. If we have no options, if we can take but one path, we are by definition slaves.