I think the moral valuesare eternal and they have been defined by various cultures and scriptures. The reason, why we see them as different at different points of time, is that the controlling powers of that time interpreted them according to their convinence and vested interest.
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There is one word only used in this bharatha varsha by people following sanathana dharma. its the word "DHARMA". no other religion has a word analogical to this word. fundametal dharma does not change. for example a dog of treta yuga and a dog of kali yuga both wag tails seeing its master. a tiger hunts deers in any yuga. a brahmin has to do his sandhya vandanam and nitya karma daily whatever be the yuga. there are desa ( country/nation) dhramas and yuga dharmas which change. eating beef in the western countries is not wrong but in our country it is considered a grave sin ( paathakam). similarly till dwapara yuga we had the aswa-medha yaagam. in kali yuga there is no such sacrifice. there are several such differences. the bottom line is what is morality. it is nothing but common sense practiced so that no living being is unnecessarily harmed or his/her rights encroached without his/her consent. this has to be practice for any society. otherwise it would have perished long ago or would