There is an old cliché that goes “the apple doesn’t fall far from the tree.” While this is usually used to describe the relationship between a parent and a child, it can also be used to describe the behavior that child exhibits. With the constant amount of research that revolves around criminalistic behaviors, the nature versus nurture debate has gained much steam. While some say criminal behaviors are acquired through one’s surroundings, other say that they are acquired genetically. In a genetic sense, the apple really does not fall far from the tree. The genes an individual is born with are the foundation of their actions, emotions, and thought process. There is a multitude of studies that prove that criminal behavior is predominantly acquired through one’s genetic makeup.

There are numerous case studies revolving around twins in regards to criminal behavior. The reason for that is twins have almost identical genetic makeups. Identical, or monozygotic, twins have nearly indistinguishable genetic DNA structure, whereas fraternal, or dizygotic, twins share around half of their genetic makeup. Because of this information, it is assumed that twin pairs also share a relatively identical environment. The nearly identical surroundings and genetic makeup of monozygotic twins make them perfect candidates for displaying the relationship that genetics has on criminal behavior. Any differences in behavior would be assumed to be because of non-shared environmental factors. (Rutter)

The first twin study is from the Vietnam Era Veteran Twin Registry. The study interviewed 3,226 pairs of male twins from all ethnic backgrounds, from ages 36 to 55 years old, and who served in the military during the Vietnam War. Of the twins interviewed, over half were monozygotic. The questions asked revolved around arrest records, felony conviction, and early-late criminal behavior. (Rutter). The study found that “neither later arrests nor later criminal behavior are significantly influenced by the common environment, but both are significantly heritable” (Rutter). This study proves that at least amongst males, there is a stronger correlation between criminal behavior after the age of 15 and genetics than criminal behavior and environmental factors.

In a YouTube interview of Adrian Raine, Raine states that “twin studies on their own show that at least 50 percent of the cause of crime and antisocial behavior can be chalked up to genes” (Raine). The other 50 percent is shared between similar environmental factors which account for very little, and non-shared environmental factors, which make up the rest. This results in the biological or genetic component making up the largest portion especially when you do not combine the two very different types of environments. However, one of the main issues with the twin studies is that some of the assumptions made on environmental factors are incorrect, specifically that twins have similar shared and non- shared environmental factors.

In order to further support and prove the findings in twin studies, a study involving full and half siblings was conducted. This specific study tested both female and male sibling pairs of either full siblings living together, half siblings living together or half siblings living apart. All of the subjects were born between 1958 and 1991, with no more than a 10-year age gap. All pairs were compared to the Swedish crime registry and properly dealt with on an environmental level. The results are as followed: “Using a range of specific models applied to full- and half-sibling pairs, we found that genetic risk factors contributed substantially to the etiology of CB, with heritability estimates ranging from 33% to 55% in females and 39% to 56% in males. Across all models, shared environmental factors were considerably less important than genetic influences” (Kendler). This sibling study also found that “estimates for the shared environment varied from 1% to 14% in females and 10% to 23% in males, which is increasing lower than those estimated in the twin study”(Kendler).

This study was able to clean up some of the flaws revolving around the twin study and more accurately prove that environmental factors, whether they be shared or nonshared, do not play as large of a role as genetic factors. It also showed that genetic factors have the largest influence on criminal behavior, with a possible influence of more than 50 percent. Although genetic makeup only accounted for about 1/3 of criminal behavior, this number is still increasingly larger than the highest percent that shared environmental factors accounted for in this study. 

A lot of people will say that there is not a “crime” gene, which is correct. Not any one gene can be entirely to blame for someone’s behavior, but that does not mean that there are not any genes linked to criminal behavior. A study of about 900 criminal offenders in Finland has recently found a trend in their genetic makeup. A large number of these criminals seem to have two common genes, one of the genes, the MAOA gene, commonly known as the “warrior gene,” is linked to aggressive and antisocial behavior, both of which lead to criminal behavior as seen amongst the most violent of the 900 criminal offenders. The other gene, the CDH13 gene, which is known for its association with substance abuse, is also known to lead to criminal behavior. Studies show that “those with the genes were 13 times more likely to have a history of repeated violent behavior” (Hogenboom). This static shows alarming evidence of genetic factors that are associated with criminal behavior that can not be influenced or affected by environment in any form.

Adrian Raine, a well-known psychologist, has conducted extensive research in this field and has been studying criminals for years. His most popular being a study conducted on murders in an American prison. The study compared the brain scans of 41 murderers to brain scans from 41 non convicted adults within the same age range and profile. What was observed was that “the murderers' brains showed what appeared to be a significant reduction in the development of the prefrontal cortex, ‘the executive function’ of the brain, compared with the control group” (Adams). This can result in risk taking and poor problem-solving skills which can both be seen in criminal. This proved there was a specific genetic component common amongst criminals that could be in part to blame for their behavior.

In addition to Raine’s study of criminal’s brain scans, he has also found other factors that seem to have a correlation with criminal behavior.  Another key part of Raine’s work was exploring a link between criminal behavior and obstetric factors. For example, some minor physical abnormalities caused by pregnancy complications that Raine talks about in Biosocial Studies of Antisocial and Violent Behavior in Children and Adults: A Review are “low-seated ears, adherent ear lobes, and furrowed tongue” (Raine 1). All of which have been linked to antisocial and violent behavior. **

There have also been a lot of studies that can link birth complications to delinquency and violence. Specifically, the birth complication of being underweight could directly cause damage to the fetus brain similar to damage observed during his study of 41 murderer's brain scans. Malnutrition as an infant can also be considered a obstetric factor that has been previously linked to antisocial and violent behavior. Visual signs of malnutrition can be a child's cracked lips and thin, or discolored, hair (Liu).

A large obstetric factor is whether or not the mother drank alcohol or smoked during her pregnancy. Both of these habits have been directly linked to conduct disorders and violent behavior in adolescence. A study of males showed “a twofold increase in adult violent offending in the offspring of mothers who smoked 20 cigarettes a day, and also found a dose-response relationship between increased number of cigarettes and increased violence. However, fivefold increase in adult violence was found when nicotine exposure was combined with exposure to the delivery complications” (Raine, Biosocial Studies of Antisocial and Violent). All of these obstetric factors can be seen as biological factors within criminal behavior.

Another factor that has shown up in Raine’s work and various other studies is a correlation between criminal behavior and low resting heart rate as an adolescent. A study was conducted on 5,000 children in Europe born in March of 1946, who had their heart rate measured at age 11. The study showed that “81 percent of violent offenders and 67 percent of sexual offenders had below-average heart rates” (Raine, Biosocial Bases of violence ). The Cambridge Study in Delinquent Development produced similar results as it measured 411 London boys resting heart rates at age 18. The results of which showed that “the boys who were convicted of violence before age 25, and those who were chronic offenders (with six or more convictions), had significantly lower heart rates”(Raine, Biosocial Bases of violence ). Resting heart rate should be seen as another genetic factor directly linked to criminal and violent behavior. However, there is no exact reason for why this correlation between low resting heart rate and criminal behavior exists. It also does not mean all people with low resting heart rates are criminal offenders, it strictly means that a lot of criminal offenders have the genetic mutation of a low resting heart rate.

Raine’s research would prove that for some of the more violent criminal offenders, there is a prominent genetic component. Despite this being strong evidence to support biological factors playing the largest role on criminal offenses, there is one flaw. Raine chose to study his own brain in addition to others and realized he had more similarities with the murderer’s brain scans than the control group. In addition to that, he was “born at home; he was a blue baby, always had a markedly low heart rate, and as plagued by cracked lips as a child” (Adams) all of which are markers and red flags for criminal behavior (Adams).

Another common distinguishing factor amongst criminals is a low IQ. There has been a series of studies conducted on the matter that came to the conclusion of criminal brains with lower IQ’s. “The IQ’s of juvenile delinquents were significantly lower than the IQ’s of comparison groups. Prospective longitudinal studies have also reported that the childhood IQ’s of juvenile delinquents were lower than the childhood IQ’s of non-delinquents” (Kandel). One common theory supporting the association of low IQ’s and criminal behavior is that sad criminal offenders with higher IQ’s are less likely to get caught, and therefore are not included in these studies.

Despite all the information pointing to Raine being a criminal, he is not. He is actually just a successful psychologist and professor. However, this does not disprove the idea that biological factors prominently impact one’s likelihood to commit criminal behavior. It merely states the environment or additional factors that contribute to this idea. Raine was also missing other key factors that have been found in criminals, such as low IQ. He should be thought of as the exception to the rule. Raine himself even states that he engaged in a lot of delinquent behavior when he was younger. He was “antisocial, in a gang, smoking, letting car tires down, setting fire to mailboxes, and fighting a lot” (Adams). All of which make sense based on his genetic makeup, but how he was able to beat the odds and pull himself out of the rebellious behavior is probably due to environmental circumstances. Professor Raine’s genetics might also explain his career choice, and why he wants to study the brains of criminals. Maybe his own genetics lead him to his career, maybe he wanted to study likeminded people. (Adams).

Adoption studies have been widely used to help prove a relationship between genetics and criminal behavior. The reason for using adoption studies is because they are able to prove hereditary relationships that are unaffected by parental relationships with that person, since there most likely not in one. Parent-child relationships are considered environmental factors and the topic of adoption eliminates that environmental factor from the equation.  A Swedish Adoption Study took place in the mid nineteen hundreds which consisted of 862 men and 913 women. All participants were born in the early nineteen hundreds with ages ranging from 20 to 40 years old during the time of the study in order to try and minimize the effect that environmental factors may have on the results. All candidates selected for this study were placed into equally economically stable adoption homes at young ages and in addition to that, the adoptive parents had zero criminal or alcohol dependency after running background checks. As it turns out, a large percentage of children whose biological parents were alcohol abusers also ended up abusing alcohol in their later adult years  (Rutter). Although this is not directly dealing with criminal behavior or acts of violence, it does prove a strong correlation between genetics and alcohol abuse similar to antisocial behavior. Both of which seem strongly affiliated with criminal behavior.

A slightly similar adoption study was conducted in Northern Europe which combined the conviction records of over 14,400 teenagers adopted out of family ages 15 years and older. This study then compared those records to the conviction records of their adoptive and biological parents in order to find a correlation in behavioral patterns that would further prove a comparable genetic factor. Information concluded on the relationships found goes as followed: “if neither the biological nor the adoptive parents are convicted, 13.5 percent of sons are convicted. If the adoptive parents are convicted and the biological parents are not the percent only rises to 14.7 percent. However, if the adoptive parents are not convicted and the biological parents are, 20 percent of sons are convicted” (Sarnoff).

In specific cases referring to property crimes, it was found that there is a strong correlation between adoptees and their biological parents committing similar crimes. However, the same could not be said for violent crimes where there was no correlation. Along with that information, there was also little to no correlation between adoptees conviction records and their adoptive parent’s conviction records (Sarnoff).

This information proves that in general genetics play a larger role on whether or not criminal offenders offspring will follow in their delinquent footsteps. Specifically for smaller less severe crime cases, genetics do play a substantial role with little to none of this correlation relating directly to environmental factors. This is because the biological parents and the adoptees do not share the same environment. Collected information also shows that the behavior of the adoptive parents, which would be considered an environmental factor, has a minimal effect on their adopted child’s behavioral patterns. According to this study, the adoptive child’s chances of committing a crime are nearly the same, regardless of their adoptive parent’s criminal behavior (Sarnoff ).

Genetics is as one may say “the be all and all” of criminal behavior. What this means is that it is the most important factor relating to the cause of criminal behavior. That is not to say that environmental factors do not play a role in criminal behavior, rather that they should just be considered the “straw that breaks the camel’s back”. Someone will behave criminally if all of their genetics point to criminal behavior, with the help of a little push from environmental factors. This can be seen in cases of privileged criminal offenders with seemingly little environmental factors.

The odds that one will demonstrate criminal behaviors dramatically increases depending on their genetics. Studies involving twins, adopted children and siblings have not only been able to prove a strong correlation between criminal behavior and genetics, but in addition show that genetics makes up majority of influencing factors. While there is not a specific genetic makeup that can guarantee a person will grow up and turn to criminal activities, there are certain genetics that can be a red flag and makes an individual more susceptible to committing crimes. Certain genetic markers that correspond with criminal behaviors are the MAOA and CDH13 gene, reductions in the development of the prefrontal cortex, low blood pressure and obstetric factors, all of which can act as red flags to those studying human behavior, genetics and criminal activity. 
