Genetic Violence: Robert an Stephen Spahalski
In The Antisocial Personalities, David Lykken compares a number of studies of twins across several cultures to try to determine how heritable violent behavior is. He concludes that certain heritable personality traits found more often in violent than nonviolent individuals — risk-taking, aggression, impulsivity, adventure-seeking and fearlessness — mean that the propensity for violence can be inherited. The Spahalski brothers seemed to have these traits. Studies of monozygotic twins found a much higher incidence of both being violent and antisocial than occurred in twins who are not genetically identical. Some of this derives from the environment, such as the culture's affirmation of violence, and some from the quality (or lack) of parenting. Even so, there are few examples of environments in which most siblings raised together become violent — even when there's abuse or parental criminality.
John Glatt gathered a number of cases of violent twins in Evil Twins, but even he failed to find many pairs like the Spahalskis. Aside from a few cases of twin mothers (Jane and Jean Hopkins, Gloria and Gretchen Graham), who killed their children together, most of the twins involved cases where one was violent and the other was not, or where they turned the violence on themselves. One of the pairs, Betty and Peggy Wilson allegedly enlisted a hit man together to kill Betty's husband. Another pair of twins, George and Stephen Spitzer, were both rapists.
The Kray twins are probably the most notorious criminal twins. Born ten minutes apart in 1933, Ronald and Reginald Kray were the sons of an army deserter. So right from birth, they had a poor role model. They developed a reputation for trouble-making, exacerbated by their boxing skills, and, after military desertions themselves, developed a criminal enterprise in London of racketeering, arson, and armed robbery. Ronnie shot a man, which appalled the other and started a rift between them. Ronnie was later diagnosed with paranoid schizophrenia. Their respective fortunes went up and down, and finally, in 1967, Reggie stabbed a man to death. An informant turned them in, and they were found guilty of two murders. They received life sentences. After their deaths, five years apart, they were buried in the same grave.
In a more updated overview of the issue of twins and violence, Gail Anderson's Biological Influences on Criminal Behavior, the conclusion is also that there is some genetic predisposition toward crime, at least as found in studies in several different Western countries. There appears to be a heritable component to property crimes, but not so much for violent crime, especially homicide. Given how few actual cases there are, this makes sense. Gregory Moffatt, in A Violent Heart, says, "Even though there are a few rare exceptions, violent individuals are not born that way. Instead they become violent through the process of cultural and sociological interaction, individual physiology, and psychological development."
A researcher who lays out the influences more precisely is Debra Niehoff, a neuroscientist, who studied twenty years of research before she wrote The Biology of Violence. She says the decision to commit violence is unique to each individual. "The biggest lesson we have learned from brain research," she says, "is that violence is the result of a developmental process, a lifelong interaction between the brain and the environment." The brain keeps track of our experiences through chemical codes, Niehoff states. Each time we experience an interaction, we approach it with a neurochemical profile influenced by attitudes that we've developed over the years about whether or not the world is safe and whether we can trust our instincts. "After every interaction, we update our neurochemical profile of the world."
Niehoff indicates that some aggressive people are over-reactive, in part because they are physiologically hyperactive, with a short attention span. Under-reactive types have trouble developing empathy; have lower galvanic skin responses and a lower metabolic rate; and fail to attach emotion to their behavior. Yet not everyone with a similar interplay of psychological and physiological factors will become violent: it requires other factors as well.