“GENETIC FACTORS IN THE ETIOLOGY OF CRIMINAL BEHAVIOUR”

Sarnoff A. Mednick, William F. Gabrielli Jr. and Barry Hutchings (1987)

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Human behaviour patterns are generally ascribed to an interaction of life experiences and genetic predispositions, but the importance of genetic influences in shaping conduct has often been contested.  This debate has been especially intense, and often emotional, in explaining criminal behaviour (Sarbin and Miller, 1970).  Reluctance to consider genetic factors in crime has had political overtones (Haller, 1968), but it may also reflect the fact that, until recently, the evidence for genetic influences consisted mainly of studies of twins, some of which were methodologically questionable.

                Christiansen (1977a) reported on the criminality of a total population of 3,586 twin pairs from a well-defined area of Denmark.  He found 52 per cent of the twins concordant for criminal behaviour for (male-male) identical twin pairs and 22 per cent concordance for (male-male) fraternal twin pairs.  This result suggests that identical twins inherit some biological characteristic (or characteristics) that increases their common risk of being registered for criminal behaviour.

                It has been pointed out, however, that identical twins are treated more alike than are fraternal twins (Christiansen, 1977b).  Thus their greater similarity in criminal behaviour may be partly related to their shared experience.  This has produced a reluctance to accept in full the genetic implications of twin research.  The study of adoptions better separates environmental and genetic effects; if convicted adoptees have a disproportionately high number of convicted biological fathers (given appropriate controls), this would suggest the influence of a genetic factor in criminal behaviour.  This conclusion is supported by the fact that almost none of the adoptees know their biological parents; adoptees often do not realize they have been adopted. 

                Two US adoption studies have produced highly suggestive results.  Crowe (1975) found an increased rate of criminality in 37 Iowan adoptees with criminal biological mothers.  Cadoret (1978) reported on 246 Iowans adopted at birth.  Antisocial behavior in these adoptees was significantly related to antisocial behaviour in the biological parents.  In a study of Swedish adoptees Bohman, Cloninger, Sigvardsson, and von Knorring (1982) found that criminal behaviour in the biological parents was significantly related to criminal behaviour in the adoptees.  This relationship held only for property crimes. 

                The study to be described in this chapter was based on a register of all 14,427 non-familial adoptions in Denmark in the years 1924-1947.  This register was established at the Psykologisk Institut in Copenhagen by a group of American and Danish investigators (Kety et al., 1968).  The register includes information on the adoptee and his or her adoptive and biological parents.  We hypothesized that registered criminality in the biological parents would be associated with an increased risk of registered criminal behaviour in the offspring.

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SEX DIFFERENCES

[…] convictions of females for criminal law violations are very infrequent.  It might be speculated that those women who do exhibit a level of criminal behaviour that prompts a court conviction must have a severe predisposition for such behaviour.  Criminal involvement of many men, on the other hand, may tend to be more socially inspired.  These statements suggest that convictions in the biological mother are more closely related to the adoptee’s conviction(s) than criminal behaviour in the biological father.

                In every analysis we conducted, the relation between biological-mother conviction and adoptee conviction is significantly stronger than the relation between biological-father conviction and adoptee conviction.  In comparison with the relation between biological-father and adoptee convictions, convictions of the biological mothers are more closely related to convictions of the daughters.  This result is statistically significant, but the relatively low frequency of female convictions forces us to interpret these findings with caution.

HISTORICAL PERIOD

The period of these adoptions (1924-67) spans some important historical changes in Denmark, including a world war, the Great Depression, and industrialization.  It is conceivable that the influence of genetic factors might be affected by these social upheavals.  It is also possible that changes in the level or type of crime during these years might influence the relations observed.  Analyses conducted for the entire population were repeated for each of the 5-year periods.  The results were virtually identical to the analyses of the total sample.  The social changes during these years did not interact with the relation between biological-parent and adoptee crime.

CONTROLLING GENETIC INFLUENCE IN EXAMINING ENVIRONMENTAL EFFECTS

In many social science investigations genetic characteristics are not considered.  In some analyses this may contribute error; sometimes omission may lead to incomplete conclusions.  For example, separation from a father is associated with an increased level of delinquency in a son.  This has been interpreted as a result of failure of identification or lack of consistent discipline.  […] some fathers who permit themselves to be separated from their child have a relatively high level of criminal convictions.  The higher level of delinquency found for separated children might be partially due to a genetic transmission of criminogenic predispositional characteristics from antisocial fathers.  If this genetic variance were partially accounted for, the environmental hypotheses could be more precisely tested.  We utilized such partial genetic control to study an important criminological variable, social status.  We separated the variance ascribable to ‘genetic’ social class and ‘rearing’ social class (Van Dusen et al., 1983).  We examined adoptee convictions as a joint function of biological parents’ social class and adoptive parents’ social class.  It is clear from inspection […] that male-adoptee convictions vary as a function of both genetic and environmental social class; log-linear analyses reveal that both effects are statistically significant.  Although the genetic effect is of interest here, we emphasize that, to our knowledge, this is the first controlled demonstration that environmental aspects influence the social class-crime relation.  This finding suggests that, regardless of genetic background, improved social conditions are likely to lead to a reduction in criminal behaviour.

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LABELLING OF THE ADOPTEE

The advantage of the adoption method is the good separation of genetic and rearing contributions to the adoptee’s development.  But the adoptions were not arranged by controlled experiments.  The adoption agency’s prime concern was the welfare of the adoptee and the adoptive parents.  Prospective adoptive parents were routinely informed about the criminal convictions of the biological parents.  This could result in the labelling of the adoptee; this in turn might affect the likelihood that the adoptee would commit criminal acts.  Thus the convictions of the biological parents might have had an environmental impact on the adoptee via the reactions of the adoptive parents.

                We examined one hypothesis related to this possibility.  If the biological parents received a criminal conviction before the adoption, it is likely that the adoptive parents were so informed; if the biological parents’ first conviction occurred after the adoption, the adoptive parents could not have been informed.  Of the convicted biological parents, 37 per cent had received their first conviction before the adoption took place.  In these cases, the adoptive parents were likely to have been informed of this criminal record.  In 63 per cent of the cases the first conviction occurred after the adoption; in these cases the conviction information could not have been transmitted to the adoptive parents.  For all convicted biological parents, the probability of a conviction in their adopted-away son was 15.9 per cent.  In cases in which the biological parent was first convicted before adoption, 15.6 per cent of the male adoptees were convicted.  In cases in which the biological parent was convicted after the adoption, 16.1 per cent of the male adoptees were convicted.  In the case of female adoptees, these figures were 4 per cent and 4 per cent.

                These analyses utilized convictions.  In a previous analysis with a large subsample of this population a very similar result was obtained by studying the effect of timing of the initial arrest of the biological father (Hutchings and Mednick, 1977).  Additional analyses by type or severity of crime revealed no effect of the adoptive parents’ having been informed of the convictions of the biological parents.  The fact that the adoptive parents had not been informed of the biological parents’ convictions did not alter the likelihood that the adoptive son would be convicted.  This result should not be interpreted as suggesting that labelling (as defined) had no effect on the adoptees’ lives.  It did not, however, affect the probability that the adoptee would be convicted for a criminal act.

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SUMMARY AND CONCLUSIONS

In a total population of adoptions, we noted a relation between biological-parent convictions and criminal convictions in their adopted-away children.  The relation is perfectly strong for chronic adoptee and biological-parent offenders.  There was no evidence that the type of biological-parent conviction was related to the type of adoptee conviction.  A number of potentially confounding variables were considered; none of these proved sufficient to explain the genetic relation.  We conclude that some factor is transmitted by convicted parents that increases the likelihood that their children will be convicted for criminal law offences.  This is especially true of chronic offenders.  Because the transmitted factor must be biological, this implies that biological factors are involved in the etiology of at least some criminal behaviour.

                Biological factors and their interaction with social variables may make useful contributions to our understanding of the causes of criminal behaviour.

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