We found significant genetic transmission effects on conduct problems for 12 out of 13 PGS at age 8 years (strongest association: PGS for smoking, β = 0.07, 95% confidence interval = [0.05, 0.08]) and for 4 out of 13 PGS at age 14 years (strongest association: PGS for externalising problems, β = 0.08, 95% confidence interval = [0.05, 0.11]). Our findings provide evidence for genetic transmission in the association between parental characteristics and child conduct problems. To conclude, our results suggest that associations between parental polygenic scores and child conduct problems at ages 8 and 14 years predominantly reflect genetic transmission.

Parent-child resemblance was accounted for by the transmission of a general liability to externalizing disorders, and this general liability was highly heritable. A highly heritable general liability accounts for the parent-child transmission of externalizing psychopathology from parents to their pre-adolescent offspring. In other words, parents pass on a general liability to externalizing psychopathology that is then manifested in their offspring in form of attention problems, hyperactivity, oppositionality, and conduct problems.

Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. This is not the same as saying that this fraction of an individual phenotype is caused by genetics. For example, it is incorrect to say that since the heritability of personality traits is about 0.6, that means that 60% of your personality is inherited from your parents and 40% comes from the environment. The heritability of a trait should not be interpreted as a measure of the extent to which said trait is genetically determined in an individual.

Twin and adoption studies have consistently demonstrated that both **genetic and environmental influences** are of major importance in explaining individual differences in antisocial behavior, including criminal behavior.[5] Concordance between twins for property crimes such as **theft and vandalism** has been generally greater for monozygotic than dizygotic twin pairs, indicating a genetic contribution.[5] However, these studies estimate **heritability of variance in a population**, and do not allow calculation of "the magnitude of the genetic contribution" to a specific individual's criminal or stealing behavior.[5]

The EXT PGS was significantly associated with a breadth of externalizing phenotypes from toddlerhood to early adulthood. Individuals with higher EXT PGS were more likely to experience conduct problems and symptoms of oppositional defiant and attention-deficit/hyperactivity disorders. A genetic liability toward externalizing is associated with a wide array of behaviors and psychiatric/substance use outcomes beginning as early as childhood and through emerging adulthood.

Evidence from twin studies shows that CPs are heritable, with approximately 50% of the variance accounted for by genetic influences. This study tested whether parental monitoring moderated the associations between genetic liability and CPs in adolescents aged 12–14. We found parental monitoring significantly moderated the association between genetic risk for externalizing and CPs in adolescence.

Heritability is an often-used term that describes the part of individual differences (or variation) in a trait or disorder in a population that is explained by genetic variation. It is often listed as a percentage that reflects the percent of variation in a trait or disorder in a population that is due to genetic factors. To be clear, heritability is never an estimate of genetic influences for one individual but a group statistic; it is always referring to the complete variation in a population.

In scientific terms, heritability is a statistical concept (represented as h²) that describes how much of the variation in a given trait can be attributed to genetic variation. An estimate of the heritability of a trait is specific to one population in one environment, and it can change over time as circumstances change. Heritability does not indicate what proportion of a trait is determined by genes and what proportion is determined by environment. So, a heritability of 0.7 does not mean that a trait is 70% caused by genetic factors; it means that 70% of the variability in the trait in a population is due to genetic differences among people.

Conduct disorder (CD) is a moderately heritable psychiatric disorder of childhood and adolescence characterized by aggression toward people and animals, destruction of property, deceitfulness or theft, and serious violation of rules. In a quantitative review of twin studies from the past fifty years, Polderman and colleagues (2015) report that ~50% of the variance in conduct disorder (broadly measured with over 200 phenotypes in 147,974 monozygotic twin pairs and 192,651 dizygotic twin pairs) is attributable to additive genetic influences. Importantly, however, these genetic predispositions have only a probabilistic relation to subsequent conduct disorder, and environmental factors can be correlated with and moderate these genetic predispositions.

Based on genomic relatedness matrices, we estimated the contribution of direct genetic effects and indirect maternal and paternal genetic effects on ADHD, conduct and disruptive behaviors at 8 years of age. Direct genetic effects accounted for 11% to 24% of the variance, whereas indirect parental genetic effects accounted for 0% to 16% in ADHD symptoms and conduct problems. The correlation between direct and indirect genetic effects, or gene–environment correlations, decreased the variance with 16% and 13% for conduct and inattention problems, and increased the variance with 6% for hyperactivity problems.

In the E-Risk cohort, **genetic influences accounted for an estimated 41% of the variance in offending**, with 40% due to shared environment and 19% to nonshared environment.[2] The authors emphasize that these are **population-level variance components**, and that even with genomic data, "polygenic scores" currently explain only a modest proportion of variance in antisocial outcomes.[2] Heritability estimates such as these cannot be used to determine the exact probability or magnitude of genetic contribution to **one child’s specific rule-breaking or stealing behavior**; they describe average effects across many individuals.[2]

In childhood and early adolescence, there is a substantial contribution of shared environmental influences in addition to heritable influences, but by late adolescence and young adulthood, familial resemblance on the general externalizing liability is almost entirely due to genetic influences. A largely inherited disposition towards behavioral disinhibition correlates and interacts with well-established environmental risk factors (parenting, peer, and school contexts) to influence the developmental trajectory of externalizing problems.

Parent-child resemblance for substance use disorders and antisocial behavior is primarily due to the genetic transmission of a general liability to a spectrum of externalizing disorders. This general externalizing liability is highly heritable, with heritability estimates of approximately 0.80 to 0.84 in prior work. Familial resemblance for externalizing psychopathology is thus largely attributable to genetic factors rather than purely environmental transmission.

The co-morbidity of externalizing disorders is largely attributed to shared genetic liability, and the heritability of a general externalizing factor has been estimated to be quite high (h^2 0.81–0.84). There was a significant association between the EXT PGS and externalizing behaviors among EA adolescents, such that individuals who scored higher on the EXT PGS also reported higher levels of externalizing behaviors. Our findings suggest that both known genetic (EXT PGS) and neurophysiological (P3 amplitude) risk markers each contribute independently to the expression of externalizing behaviors.

Heritability, in a general sense, is the ratio of variation due to differences between genotypes to the total phenotypic variation for a character or trait in a population. A second problem with heritability estimates is that they measure variation only within populations. In other words, a heritability estimate cannot be used to determine the causes of differences between populations, nor can it be used to determine the extent to which an individual’s phenotype is determined by genes versus environment.

Heritability measures portions of population variation in traits associated with genetic variation, but that does not imply that heritability generalizes across places and times. Heritability is only meaningful for a specific population at a specific time. To understand why heritability estimates are no longer important, it is necessary to understand that they are completely dependent on the specifics of the samples and environmental conditions from which they are taken. Thus, high heritability does not mean that an individual’s trait is fixed or that environmental interventions are useless; it only describes the proportion of variance attributable to genetic differences in that study population.

Reviews and meta-analyses concluded that **antisocial behavior is genetically influenced** with heritability estimates ranging from 0.32 to 0.56, averaging to approximately 0.50, meaning about half the variance in antisocial behavior and crime is attributable to genetic factors.[17] However, the chapter stresses that "we still do not know which genes are implicated for certain and are unable to explain more than a modest portion of the variance" and that **no causal relationship can be determined at the individual level**.[17] Heritability estimates from twin/adoption or GCTA studies are **group-level statistics** and "do not tell us how much of a particular person’s antisocial behavior is due to genetic versus environmental factors".[17]

This broad “externalizing” factor has been found to have a large heritable component (e.g., heritability = .80–.85). For instance, one study found general genetic liability across conduct disorder, adult antisocial behavior, alcohol dependence, and drug dependence increased one’s risk for developing any/all of these externalizing phenotypes in parent-to-child transmission. Collectively, accumulating evidence appears to indicate that genetic predisposition for externalizing behavior and substance use are primarily associated with externalizing behaviors in early- to mid-adolescence and substance use in adolescence and early adulthood.

Heritability: the proportion of population variation in a phenotype that is due to genotypic differences. It is important to emphasize that heritability is a property of populations, not individuals. Behavioral geneticists partition phenotypic variance into genetic and environmental components, but these quantitative models estimate contributions as constants for entire populations and do not specify how much of a given individual’s behavior is caused by genes versus environments.

Meta-analyses suggest the level of **heritability of antisocial behavior is approximately 40–60%**, with shared environmental factors explaining about 11–14% and nonshared environment 31–37% of the variance.[9] A variety of psychological constructs associated with antisociality/criminality, such as intelligence, personality, and mental health disorders, have also been found to be heritable.[9] The article underscores that these estimates refer to **variance in a population**, and that biological explanations cannot at present be used to determine the degree to which **one individual’s criminal or stealing behavior** is genetically caused.[9]

Conduct disorder is a moderately heritable psychiatric disorder of childhood and adolescence. In this review, we discuss behavioral genetic studies of CD and CD symptoms, including evidence that CD is moderately heritable and that CD shares genetic influences with other externalizing spectrum disorders. However, we also emphasize that genetic influences on CD are probabilistic, not deterministic, and that shared and nonshared environmental factors contribute importantly to CD risk. Gene–environment interplay (correlation and interaction) is also highlighted as an important mechanism by which genetic and environmental factors jointly influence CD.

On average, about 50% of the variance in antisocial behavior, broadly defined, is explained by genetic effects, with the remainder being accounted for by shared and nonshared environmental effects. Most familial transmission of these symptoms appears to occur through a general vulnerability factor that is highly heritable (h^2 = 0.80). Genetic factors have been established unequivocally for externalizing spectrum symptoms and traits, with considerable evidence for a highly heritable general liability factor. However, heritability estimates describe population-level variance and do not allow precise calculation of the genetic contribution to a specific individual’s behavior.

Such conclusions, however, are based on quantitative models of human individual differences that estimate genetic and environmental contributions as constants for entire populations. They can not conclude that a specific person's extraversion level is “50% genetic;” the concept of heritability applies not to individuals, but rather, to differences among many individuals. Stated in statistical terms, heritability applies to the variance of a set of observations, rather than to a single specific observation.

Twin and adoption studies show persuasive evidence that **both genetic and environmental factors contribute to antisocial behaviour**, and that antisocial behaviour often clusters within families.[15] However, the Australian Institute of Criminology notes that "there is no single gene, or even a small number of genes, that predict an increased risk of antisocial behaviour" and that where susceptibility variants have been found, **each gene contributes only a small amount to overall liability**.[15] These susceptibility alleles "only increase risk" and "are not deterministic and only poorly predict the likelihood that an individual will engage in such behaviour"; risk estimates (e.g., ~1.5 times risk) are again **population-level** and cannot quantify the genetic share of a specific person's offending or stealing.[15]

Using a large, population-based cohort of individuals aged 8–21, we showed that externalizing psychopathology in the first two decades of life is under considerable genetic influence. In contrast, we found externalizing psychopathology to be significantly and moderately heritable, with genetic factors explaining 46–58% of the variance. We did not find evidence for novel genetic factors on externalizing throughout this developmental period, rather we found a decrease in genetic variance, and increase in environmental variance. These estimates describe variance at the population level and cannot be used to partition the causes of externalizing behavior for a single child.

Overreactive parenting predicted more child externalizing behaviors. Attending center-based early care and education was associated with increasing externalizing behaviors only for children with genetic liability for dysregulation. Additionally, children who were at risk for externalizing behaviors due to both genetic variability and exposure to center-based ECE were more sensitive to the effects of overreactive parenting on externalizing behavior than other children, illustrating gene–environment interaction and that genetic liability does not operate deterministically at the individual level.

Heritability estimates only apply to populations, not to individuals, and the word “heritability,” in this context, must not be confused with “genetic inheritance.” Heritability is defined as the proportion of variance in a trait that is attributable to genetic differences among individuals in a specified population. Thus, high heritability of a behavioral trait does not mean that the trait is immutable or that one can calculate how much of a particular person’s behavior is due to genes. Behavioral traits such as aggression, antisocial behavior, and other externalizing problems show non-zero heritability, indicating genetic liability, but this is about variation in the group, not about assigning fractions of causation to an individual child.

In a family-twin study, Hicks et al. found that a highly heritable (80%) general vulnerability to all the externalizing disorders accounted for most of the familial resemblance. Genetic epidemiologic studies indicate that personality disorders and externalizing conditions are modestly to moderately heritable, but individual-level risk remains the product of multiple genetic and environmental influences. Heritability estimates reflect the proportion of variance in liability due to genetic factors across the population and cannot be interpreted as the proportion of an individual’s disorder that is ‘caused’ by genes.

Behavioral genetics studies often estimate heritability, which is the proportion of individual differences in a trait that is associated with genetic differences among individuals in a population. Concluding that a trait is heritable does not mean that it is solely influenced by genetics and unmodifiable by environmental factors. Further, heritability estimates are specific to the sample in which they are obtained and can change depending on environmental context. A complete understanding of human behavior and individual differences therein requires an understanding of both genetic and environmental contexts. All complex human behavioral traits are partially heritable, which also means that individual differences in all complex human behavioral traits are influenced by the environment.

A review of genetic variants associated with antisocial behaviour concludes that, although some variants can influence cognitive processes like moral judgment and impulse control, "there is currently **no evidence that carriers of these mutations are, per se, incapable of intentionally committing crimes".[6] Most studies are case–control and authors agree on "the importance of the combination of **genetic predisposition and social/family environment**".[6] The paper notes that available evidence **does not support using specific variants or heritability estimates to determine the degree to which a particular individual's criminal acts are genetically caused**, limiting their forensic value.[6]

Quantitative behavioral genetics studies provide strong evidence for heritable influences on the development of externalizing spectrum behaviors that cut across traditional diagnostic boundaries, including attention-deficit/hyperactivity disorder, oppositional defiant disorder, conduct disorder, antisocial personality disorder, and substance use and dependence. Behavioral genetics research indicates substantial heritable influences on the development of oppositional defiant disorder and conduct disorder. These heritability estimates are population statistics and do not imply that the behavior of any particular child is determined by their genes. Environmental factors and gene–environment interplay are also critical.

In childhood and early adolescence, there is a substantial contribution of shared environmental influences in addition to heritable influences on externalizing. Multiple studies have now demonstrated that the genetic variance of externalizing increases in the context of greater parent-child conflict, negativity, punitive discipline, and lower parental warmth. A largely inherited disposition towards behavioral disinhibition correlates and interacts with well-established environmental risk factors to influence the developmental trajectory of externalizing problems, underscoring that heritability estimates do not specify the extent to which genes caused any one child’s specific behaviors such as stealing.

Heritability is not the proportion of a phenotype that is genetic, but rather the proportion of phenotypic variance that is due to genetic factors. Heritability is a population parameter and, therefore, it depends on population-specific factors, such as allele frequencies, the effects of gene variants, and variation due to environmental factors. Consequently, one cannot take a heritability estimate derived from twin or family studies and apply it to determine the degree to which a particular individual’s trait value is caused by genes. Estimation of heritability in populations depends on the partitioning of observed variation into components that reflect unobserved genetic and environmental factors.

In a longitudinal sample, genetic factors, parenting, and self-control all contributed to criminal behavior, with parenting partially mediating genetic effects.[12] The study used behavioral genetic methods to estimate **heritability of criminal behavior and self-control**, but did not attempt to and explicitly could not calculate "how much" of any given participant's offending was due to genetics.[12] Behavioral genetics research generally recognizes that **heritability is a population statistic** and "cannot be applied to individuals to apportion responsibility or causation" for specific acts.[12]

Heritability estimates from twin analyses ranged from 50% to 80% for conduct disorder, attention-deficit/hyperactivity disorder, and oppositional defiant disorder. Our data suggest the comorbidity among CD, ADHD, and ODD is primarily explained by shared genetic influences; however, each disorder was also under unique genetic influence. These findings support a shared genetic liability to externalizing disorders but also indicate that environmental factors and unique genetic effects contribute to individual differences. Heritability estimates do not specify the extent to which genes contribute to any one child’s conduct problems.

Expected or realized genetic similarity between relatives (either close or distant) can be used to estimate heritability of complex traits in human populations. These methods produce estimates of total heritability, or of the genetic variance explained by measured SNPs, at the population level. However, estimates based on close relatives generally yield high precision but may come with bias due to strong assumptions that are violated, and all such estimates remain group-level parameters; they do not allow precise calculation of how much of an individual person’s complex trait is due to genetic versus environmental causes.

Jones summarizes behavioral genetic research on criminal behavior, stating that "research has shown that **genetic influences account for a significant portion of the variance in criminal behavior**, but environment is equally or more important".[16] He emphasizes that "it is more often an **interaction between genes and the environment** that predicts criminal behavior" and that twin/adoption research designs estimate **group-level heritability**, not **individual-level genetic responsibility**.[16] Thus, family history and heritability estimates can indicate increased liability to externalizing or conduct problems, but not the magnitude of genetic contribution to one child’s stealing.[16]

Results from multivariate path analysis indicated that externalizing polygenic scores were directly associated with adolescent externalizing behavior but also indirectly via peer substance use in the European ancestry sample. Studies indicate that genetic influences account for approximately 50% of the variation (range ~20–80%) for each individual phenotype in the externalizing spectrum in the population. Importantly, individual externalizing-related phenotypes load on a shared genetic factor, which is highly heritable (~80%). These estimates quantify variance in the population and cannot be used to calculate the magnitude of genetic contribution to a specific individual’s stealing or rule-breaking behavior.

A research starter on "Criminality and genetics" notes that while a number of genes (such as **MAOA**) have been investigated, "no definitive causal link to criminal behavior has ever been established in individuals with a MAOA abnormality".[14] It describes heritability studies showing genetic influences on antisocial behavior, but stresses that such findings **cannot be used to predict or quantify criminal behavior in specific individuals**, and that environmental factors and personal choice remain crucial.[14]

Heritability estimates for conduct problems based on twin studies are 40–70%. These figures indicate that genetic factors account for a substantial proportion of variance in conduct problems in the population. Nonetheless, conduct disorder and related behaviors such as theft are understood to arise from complex interactions between genetic predispositions and environmental influences, and heritability estimates do not permit precise attribution of an individual child’s behavior to genetic versus environmental causes.

In fact, the influence of genes or environments on any given person may differ substantially from the group-average statistic of heritability. Everything—height, intelligence, personality, even behaviors such as rule-following or rule-breaking—is a little bit heritable, but heritability estimates tell us about variation in a population. They do not tell us exactly how much of a particular individual’s behavioral outcome is due to genes. Thus, a child might have inherited liability for externalizing behavior, yet the specific occurrence of stealing or other rule-breaking at a given time may be more heavily influenced by that child’s unique environment.

Behavioral geneticists and psychologists introduce heritability in the following way: Heritability is the proportion of phenotypic variance that is attributable to genotypic variance: heritability = VG/VP. Heritability is therefore a measure of how much of the variability in a trait, within a population, can be statistically associated with genetic differences. Philosophical analyses emphasize that such variance ratios are silent about the causal contribution of genes and environments to the trait level of any single individual, and that interpreting heritability as "the degree to which a trait of an individual is genetically determined" is a conceptual mistake.

This handbook chapter on "Genetics and Crime" reports that a meta-analysis of 51 twin and adoption studies found a **heritability estimate of 41 percent** for antisocial/criminal behavior, with the remaining 59 percent due to environmental factors.[1] The chapter states that "there is no question that genetic influences are important" but that "heritability estimates for criminal behavior are only moderate at best" and reflect **variation in a population**, not a measure of "how much" genes caused a specific person's criminal or stealing behavior.[1]

Background knowledge in behavioral genetics holds that **heritability is defined as the proportion of phenotypic variance in a population attributable to genetic variance**, not a property of individuals.["KNOWLEDGE_BASE"] Standard texts emphasize that one cannot say "this child’s stealing is 40% genetic"; instead, a heritability of 0.4 means that, across many children, 40% of the differences in stealing propensity are associated with genetic differences.["KNOWLEDGE_BASE"] Consequently, although an 8-year-old’s family history of externalizing or conduct problems may indicate an **elevated genetic liability** to rule-breaking, the **magnitude of the genetic contribution to that individual child's repeated stealing cannot be calculated** from heritability estimates or pedigree alone.["KNOWLEDGE_BASE"]