alright so why do we feel guilt... the evolutionary advantage of guilt not "because God wants us to feel bad for doing bad things."
in my opinion i think that we feel guilt because when we do feel guilty it is usualy because we killed/hurt something/someone, we stole something, we lied, we had an affair,etc.
the purpose of feeling an unpleasing stimuli is to keep us from continuing to do the task. this might be to keep us from, lets say you are stealing money from your room mate. because you migt be caught stealing from your room mate or he/she might become suspicous. so thouse who felt guilt must have avoided doing risky things to acheive more... and maybe because of that they were liked more so they had less enemies/rivals and being liked by the group must have meant that they wouldn't get a club in the back of the head while out hunting or gathering.
just my suggestions post your suggestions here and maybe we can figure this out... if it has been figured out then teach please so we can find anny holes in it and test the crap outta it >_<