Morals and ideas are a result of biology. Thoughts and the brain cannot be independent from each other. I wouldnt go as far to separate "nature" and "human convention" as if morals come from one and not the other.
I think morality is relative. Without a christian Bible, to tell people what morality should be, people would've been forced to come up with their own. Therefore, making morality a personal opinion, which I think is based off of an individuals level of empathy.
@NDECD1441 The problem with moral subjectivism is if morality is nothing more than subjective opinions, moral praising and blaming would be equivalent to praising a movie genre you enjoy and blaming one you dislike. And moral subjectivism claims moral judgments cannot be meaningful propositions one could argue about, they're neither right nor wrong. David Hume's emotive theory and A.J. Ayer's verification principle both argue this. Both theories do not explain the empirical data; people do meaningfully argue about right and wrong.