There is no conclusive proof that violence is within a person from birth. In many cases it is clear that genetics have nothing to do with some offenders’ criminal behaviour. Most scientists and mental health professionals have agreed that violent tendencies can come from a person who witnessed violence in their childhood or were abused themselves.
While evidence does exist that shows violence is genetic, no one has conclusively proved that violence starts at birth. Many scientists claim that there is no such thing as an “evil gene.” Dr. Andrew Raine, in the Psychopathology of Crime (Academic Press, 1993), wrote that there is no single gene capable of producing criminal behaviour. However Dr Raine also wrote that data from certain sources has shown some evidence of there being a genetic link to crime and violence.
Florida State University behavioral geneticist Dr. Glayde Whitney believes that one day science will be able to answer these perplexing questions. It is only a matter of time until scientists will have the answers to what part of human behavior is biologically determined from birth and what part comes from the environment and childhood. Whitney also stated that in most cases of violent crime both genetic and environmental factors are at work. What scientists want to know is to what degree. When it comes to criminal behaviour and violence, Whitney believes that up to 50 percent of this behaviour may be genetic.
Geneticists thought that they had found proof back in the 1960s. A presence of an extra Y chromosome was discovered, which is an extremely rare condition, and this was linked to violent offenders. This gained a lot of attention; however, further studies showed that the condition was not hereditary, it was very rare and, when compared with the amount of crime that occurs, this simply did not add up.
Researchers also found that the hormone testosterone can contribute to aggression and violence in humans. Whitney believes that this research suggests the capacity for making and reacting to testosterone – regardless of someone’s environment - is as genetically programmed as the color of a person's eyes.
Experiments have been done at John’s Hopkins University with lab animals. It was discovered that the absence of one single gene in mice can see them turn into vicious, over-sexed killers. If a mouse is raised without the gene that makes nitric oxide, the mouse might display aggression. Nitric oxide is an important brain chemical. It is also believed that nitric oxide acts on serotonin, which is supposed to inhibit aggression in humans.
Bruner conducted a study on Norwegian males from a violent criminal family. Testing the urine of these men revealed a lack of monamine oxide in their bodies, which is associated with violent actions. This experiment supports the nature theory; however, it could have been due to environmental factors that caused the loss of monamine oxide or these men may have grown up around violence and unhealthy situations.
The conclusions drawn from the research and experiments carried out show that there is a very big likelihood that violence is genetic. It is hoped that scientists will come to a conclusion regarding this issue, because in recent times they have argued a lot about this issue. Many are split on whether there is enough evidence to make the claim that a violent person was born this way.