Modern neuroscience is beginning to substantiate Darwin's notion that the roots of human morality lie in social instincts, present in several species. The role of primitive motivational-emotional systems in human morality still remains under-recognized, however. Based on recent experimental evidence and classic neuroanatomical data, we here portray a view of how "ancient" limbic-neurohumoral systems of social attachment and aversion are crucially involved in human moral behaviors, including altruism, empathic concern and aggression. Rather than being a mere evolutionary remnant of our ancestors, such limbic-neurohumoral systems are tightly integrated with cortical mechanisms to enable complex moral sentiments and values, which powerfully influence our choices in socio-cultural settings. Exploring the underlying mechanisms of human social attachment and aversion will provide new insights and foster novel experimental paradigms for the study of moral cognition and behavior.