I am aware of 2 brain anomalies that seem to be associated with the non-emergence of a conscience. One is associated with psychopathy. The other is associated with narcissism.
My understanding is that a psychopath has a smaller and misshapen amygdala and that the connectivity between the amygdala and ventromedial prefrontal cortex is nearly non-existent. My understanding is that psychopaths experience weaker pain signals than non-psychopaths. Fearlessness is often attributed to them. They apparently have the ability to feel empathy for others, but they simply choose not to. The inability to delay gratification and to learn from life experiences are also traits which have been associated with psychopathy.
One interpretation of this is that persistent pain which is strong enough to induce a rumination that does not relent until a means of avoiding such pain in the future has been discovered, is a necessary precondition for the emergence of a conscience.
My understanding is that narcissists, by contrast, have a lack of grey matter in the left anterior insula and that this has been associated with an inability to experience affective empathy.
This evidence seems to suggest that these 2 are necessary preconditions for the emergence of a conscience:
1: the ability to experience persistent pain necessary to induce rumination
2: the ability to experience affective empathy
From an experiential perspective this makes intuitive sense because when our actions lead others to suffer, feeling the suffering of others as if it was our own intensely (guilt) is the force that gives rise to the voluntary decision to obey moral prohibitions and to be guided by genuine care and concern for the wellbeing of others in the future in order to avoid experiencing this intense pain again.
Are the 2 preconditions all that is necessary for a conscience to emerge?