Ethics is systemetized morality, definitely not natural. Morality has a number of sources or causes, some of them natural, some of them learned. Here's my list of the sources of moral principles: love, empathy/compassion/sympathy, values, beliefs, desires, fears, judgment and condemnation/hatred, personal experiences, peers/societal influence/groupthink, etc. (I'll let you decide which ones are natural and which ones are learned.)