Researchers discovered evidence that certain people inherit a genetic make-up that predisposes them to hostility and violence. According to experts, the "poor behavior gene" is triggered only if they were ignored or mistreated as children. 20% of the population has this gene triggered by childhood adversity, such as physical abuse, emotional neglect, or family instability.
This idea is supported by research showing a correlation between having one or more delinquent siblings and an increased risk of becoming a criminal yourself. This correlation has been reported by different studies for both boys and girls. It has also been reported that parents of juvenile offenders are more likely than other parents to have similar problems themselves as children. These findings suggest that delinquent behavior is caused by a combination of biological factors and social learning from the environment around them.
Does this mean that criminals can't change? No. Studies show that once individuals with a criminal history discover what life choices lead away from crime, they tend to make changes to protect themselves and their families. The key is not to re-create the circumstances that led up to their problem in the first place. Although genetics play a role in criminality, so does every other factor that influences an individual's life decisions: family history, peer pressure, opportunity costs, etc.
According to experts, a single gene may explain why some males, but not all, who are molested as children grow up to be violent or aggressive. The gene variant appears to be activated solely by childhood abuse, yet it is detected in one-third of the men and young boys investigated, according to the researchers. They suggest that this gene may be responsible for creating "a vulnerable brain" in abused children that makes them more likely to commit acts of violence as adults.
Abuse can change a person's brain chemistry to make them more prone to committing future acts of violence. Abused children are three times more likely than their non-abused peers to die by suicide. Adults who were sexually abused as children are nine times more likely than others to become rapists. Those who were physically abused as children are four times more likely to beat their spouses or partner up physically.
Studies have shown that women who were sexually assaulted as children were more likely to experience depression and anxiety later in life. Men who were sexually abused as children had higher rates of sexual problems such as impotence and decreased libido. Both sexes who were abused as children were more likely to use drugs and drink too much alcohol.
The link between childhood abuse and adult health issues has been recognized by scientists who study trauma, who note that many people who were once thought to have bipolar disorder or schizophrenia actually suffer from post-traumatic stress disorder (PTSD) related to early abuse experiences.
Genes that are violent However, until recently, no genes have been linked to severe or recidivistic violent behaviors such as homicide. According to a meta-analysis of data from 24 genetically informative research, genetic effects explain up to 50% of the overall variance in violent behavior. The authors found evidence for moderate genetic effects across multiple measures of aggression in both children and adults.
The analysis also found evidence for shared environmental influences on violence among full siblings, suggesting that experiences during childhood and adolescence influence how likely they are to engage in violence as adults. The study did not examine potential mechanisms for this effect. It is possible that similar factors are at work for both siblings; for example, if one child exhibits aggressive behavior, others may learn that it is acceptable to fight back or take risks to get what they want.
Overall, the findings indicate that genetics play a role in individual differences in violence but also suggest that environments can play a significant role in shaping how individuals act violently.
Decades of study have revealed that genetic and environmental variables both impact a wide spectrum of human and animal behaviour (e.g., Grigorenko & Sternberg, 2003). However, the genetic basis of hostility is still unknown. Research on animals has shown that genetics plays a role in aggression, but this relationship is not simple because the presence of a parent or sibling who is also aggressive does not mean that the tested animal will behave aggressively himself/herself. Environmental factors such as socialization can influence an animal's tendency to be hostile or not, even if they are raised by the same parents.
Studies have shown that there is a correlation between siblings' levels of aggression. If one sibling is found to be aggressive toward other animals or people, the other may follow suit. This means that there must be something about the person that makes them more likely to be aggressive; perhaps it is inherited from their parents. Scientists used to think that siblings shared 100% of their genes, but now we know that only shares around 50%. So, if one sibling is found to be aggressive, it isn't difficult to see how the other might also be given that they share half of their DNA.
It has been suggested that children who witness violence between their parents are at risk for becoming violent themselves.