@mwurgler,
What do you mean when you say our deepest moral beliefs are shaped by nature? Do trees, cats and rivers shape our moral beliefs?
Morality is a universal human trait -- hardwired into our brains. Anyone's individual response to a situation on moral grounds would vary depending on both the programming hardwired deep in the recesses of the brain and their unique life experiences.
For example, the brain circuitry that governs morality is pretty screwed in psychopaths.