The genetic and developmental formula behind psychopathic individuals is discussed in this Jim Fallon keynote. The neurobiologist talks about the various factors that impact a brain while it's developing in the womb and during early prepubescence.
Fallon noticed that in all the specimens studied the MAOA gene was heavily expressed. The MAOA gene is sex-linked which means that individuals can only get it from their mother and which is why most serial killers tend to be males. However, in order for the MAOA gene to become expressed, the individual has to be exposed to a severe traumatic situation during early prepubescent years.
What this discovery reveals is that in areas of the world where violence is widespread, individuals are choosing mates who are particularly assertive and aggressive, creating generations of children that are particularly prone towards hostility.