new studies however suggest that some gene variants may be connected to aggressive behavior. notorious serial killer charles manson had a mother and uncle who were criminals is that significant. it seems that what our genes influence is not our character but chemicals in the brain violent people may have lower levels of the neurotransmitter sarah tone and too little sarah toning in the brain can lead to uncontrolled aggression. damage to the frontal lobe of the brain can also make people more volatile one famous case is the american railroad worker phineas gage in one thousand nine hundred eighty eight an explosion drove an iron rod through his head gage survived and the bar was removed but his personality changed he suddenly began drinking alcohol and became violent and combative. so it's not just biological factors that dictate criminal behavior traumatic