Why do humans, or any living creatures for that matter, possess a sense of morality and ethics?

There are, of course, plenty of theories (and various blends of ideas) as to why humans have certain moral or ethical standards, but what is it about our physical brains that causes us to experience these intangible concepts like guilt or a sense of right and wrong? If we assume that there is such a thing as free will, why do humans have the tendency to want to do the right thing despite having the freedom to do otherwise?<br><br>It's easy to apply some logic and consider that personal experience, environment, belief systems, upbringing, and even instincts may play a role in shaping our moral compass, but I see those factors as supplementary influences that modify or shape our moral code. I'm more curious as to what is the root cause that allows us to have a moral compass in the first place? That is to say, what is it about human biology and/or neurological processes that manifests as the experience of ethical decision making?