I think guilt is/was very much something cultivated and abused by a certain religion, in order to manipulate people into submission. For example, the idea that we are all born sinners, and have to be salvaged from this congenital fault.
When I grew up I was subject to these ideas (not through family, but society), and therefore felt guilty about most things. I even felt guilty about being a female, as there was so much focus on gender roles. I felt guilty about being a non-believer (but they still managed to put the guilt into me!). Luckily I left town before I went completely mad.
Now, being older (and wiser....?), I know I was also suffering from guilt of not being true to myself.
So is guilt something in-built in the human mind, or is it mostly religion-based? I'm not so certain any more.
I have seen my cat looking awfully guilty on several occasions, so maybe it is an in-built thing. (Unless Puss has been sneaking off to church without me knowing it).