Ethics are based on cultural mores, which are the relatively fixed moral attitudes or customs of a societal group.
Explanation:
Cultural mores, in simple terms, are the rules that a society or a community sets for itself. The basis of the ethics possessed by an individual who is part of a larger community or society is the cultural mores that the community follows.
An individual who is a part of such society has to live by the cultural mores collectively actuated by society. These cultural mores ultimately become the source of the individual's ethics.