Ethics is not an invention, understood as something new or something that did not exist before. Ethics is a practical condition that distinguishes the human being from the rest of living beings. When asked what should I do? the human being discovers that he can modify his present and build an argument that justifies the present change and nourishes a hope, goal or ideal in the future.
On the other hand, the human being discovers through the formulated question that norms, rules or maxims of conduct can be imposed.
Ethics is a discovery, because people can not invent the ethical, the ethical is a social fact, that transcends the man, the man acts, and his performance can be ethical if it fits the social conventions, or unethical if it does not. Now the social convention is not an invention either, it is a process of spontaneous and evolutionary discovery. Therefore, it was ethical to make human sacrifices in antiquity and today is a deplorable fact.
I received your answer at such a moment when I was just writing on the same issue that has concern to my present project. Here I produce the same paragraph and perhaps you will realize some alignment in our views.
"When man was in primitive life, he made his living on his natural abilities only. We all are aware that any conflict between two creatures generally gets settled by the application of natural abilities with them to up held one’s own interest. Both were at liberty to apply their all the possible abilities to overpower the rival. However, it is a fact; both were with their natural abilities only. Generally such struggle and conflict might result into killing or contracting mortar injury to either or both the sides also. But the instinctive knowledge had taught each and every creature to remain aware or conscious about its own limitations before entering (or during) a conflict or struggle to safeguard or realize its interest. Either side has to abandon its claim and might manage to escape from the worse. Here, there was no place of ethics according to their comprehension that is defined and understood by man today. Wild life system has its own ethics, but it can never be comparable with human social system. I believe our comprehension and recognition of ethics changes as per socio economic formation in which we make our living. The understanding and philosophy of ethics that was adopted by the people living in the age of Plato were different in the age of Abraham Lincoln and Marx."
It is true what it indicates. We could add that ethics is a condition to modify reality, through norms, procedures or values at a given moment. This, in turn, must be visualized in historical contexts. Greetings.