I will put fourth the idea that there is some form of innate morality. Best described by the golden and silver rules. I put this forward based only on my on personal experiences in life. Though being good vs feeling guilt and shame; seem obvious. I know you could argue that those are societally ingrained into me and I would say yes that is part of it. Though I would in turn point out that if there was not also a physical aspect that caused a natural sense of morality societies would have been very difficult to form. The understanding of mutual benefit comes from a sense of morality I think.