I kinda agree with james brown its not biological it is a learned response. Look at the myth of the garden of eden man did not know they were naked till they ate the fruit. A baby is not ashamed that he pooped his diaper but a 2 or 3 year old is conditioned to start to feel guilt or shame.
I like this video its about sex but you can insert any negative emotion to what he is talking about. When you are conditioned at a young age to feel guilt for something to be forgiven you have to go back to the source that told you it was wrong or conditioned you to feel guilty.