After all, our cultures are also determiners of what is right and wrong

I absolutely agree with this. I was surprised to know that many things that are looked upon as "abomination" by our culture are welcomed in some other places. After all, culture is the people's way if life, and like you said, it shows us what is good and bad.

However, in my own opinion, something can be culturally right, but it might not be moral in the remote sense. This is why I, sometimes, tend to think that morality is without recourse to culture (my opinion though; I might be wrong).

Are we born virtuous and then corrupted by the social world?

I've asked myself this same question. Sometimes you'll hear this phrase "as innocent as a child", making people to think that humans are born without corruption and the social world is to be blamed for our corruption.

The reality is that we are born with both selfish and competitive, as well as cooperative and fair predispositions, which have all proved to be adaptive during the challenges of our species’ evolutionary past

This statement has provided the answers to the questions I've been asking myself.

Welcome back Abbey. Missed your posts so much