I would disagree with the idea that individuals have an inherent sense of ethics.   In fact I have had occasion to note this problem just recently.   Two children from the same family--a family that has unfortunately little time for their children. One has had wonderful care by another person, starting about 6 months.   The other only started with that person at about 4 years old. By then she was set in her incredibly selfish ways--no sign of a sense of ethics whatsoever.   Her brother is a delightful, caring person, always willing to cheer others on, willing to win or lose, etc. none of which his sister would ever do. She even was unwilling to let the friends she had invited to her 9th birthday party have any cake, or sing her "Happy Birthday"--though she was willing to take the presents. The caregiver is trying to bring some sense of ethics and fair play to the sister--but it's an uphill struggle--the parents seem to be afraid to criticize her in the least--so she runs wild.   Storing up big trouble for teenage years, it appears.

It seems clear to me that ethics must be taught.

This inculcation of a moral code is one of the main goals--and advantages of many religions.   True, it is not necessary to be religious to set a good example--obviously.    But some setting of moral guidelines is necessary.

The family in question is not at all religious.   But that is not crucial. What is crucial is that they do not try to guide their children.   The boy has gotten good guidance elsewhere.   The girl is already seemingly past receiving guidance.   We hope this changes soon.
It is not at all clear that a sense of ethics comes naturally.