The lack of this understanding allows them to be deceitful without feeling bad about what they do. The official term would be "emotionally retarded". When it comes to the heredity I mentioned, there are links to families with a pre-disposition to commit crimes, alcoholic parents, and lack of discipline from parents for irresponsible behavior ("Anti-Social Behavior"). There is also a link to pathology that stems from brain abnormalities. 21 men diagnosed with this disorder all had a subtle abnormality in their frontal lobes. These men had an 11 percent reduction in the gray matter of the frontal lobe. It should be noted that the brain's frontal lobe is closely involved with responses to fear and stress, as well as with planning and other aspects of cognition. It was also shown that people who suffer trauma to this part of their brain begin to exhibit antisocial behavior (becoming irresponsible, untrustworthy, and inappropriate in social situations). However it's stated that it's not just the frontal lobe, but many different regions of the brain malfunctioning that add to ASP disorder ("Brian Abnormality linked to pathology" by Erica Goode). .
As to the symptoms of a sociopath/psychopath, there are almost too many to list. As a child, they will exhibit feelings of inadequacy, and because of this they will be targets of ridicule. The child will also be incapable of following rules. They will eventually bully others themselves, skip school, run away from home, steal, and in extreme cases, torment small animals. It's possible that the child will also develop ADHD. The child will also drink, do drugs, smoke and become sexually active a lot earlier than their peers. The disorder tends to become less obvious though as the person enters there thirties, but the signs are still there. They get great joy in the act of hurting others for absolutely no reason. The drug and alcohol abuse will also follow them into adulthood.