Where does guilt come from?

What’s the natural purpose of guilt? If someone does an evil action why should they feel bad? Can they change it? Let’s use an extreme case, someone murders and immediately committs suicide.

It’s your fault? So what?

If there is a super-natural plain, perhaps they are hurting their loftier self by doing evil?

If the world is natural, the only explanation I could think of is, we evolved with guilt in order to maintain order amongst our kind. If that is the case, shouldn’t guilt come before the act? Why does guilt come after an irreversible action? Did we evolve with a glitch?

In my soul search I often imagine human evolution. When it comes to guilt I just don’t see where is belongs. Survival of the fittest means your fitter if you outlive someone. Shouldn’t it make you happy that someone else is dead?

Why would a rich man commit suicide?

Before writing this post I did a Google search on “rich man commits suicide”, there was no lack of stories.

How is it physically possible for someone to take their own life?

Is it in order to feel better? If you stop existing you won’t be at all. Doesn’t it seem that people know there is an afterlife? When a situation gets really bad people think it’s worth the gamble to die and try the next thing.

Let’s take it further;
If we are only physical them all we should care about is food, shelter and procreation. Why would a rich man commit suicide? I’m not referring to a man who lost his money, I’m referring to a rich man is his peak. He could buy all the food he wants. He could have a bigger home then he could use. I’m sure he would not have a hard time finding women ready to live with him.

Could you give a natural explanation?