Social Factors Play an Important Role in Human Behavior

Zhang Qiming

PureInsight | September 23, 2002

On August 2, 2002, Science Magazine reported the findings of a study, which proved that a protein code gene that breaks down neurotransmitters, could increase the possibility of human crimes together with the influence of the social environment.

A team, led by clinical psychologists Moffitt and Caspi, both from King’s College in London and the University of Wisconsin- Madison, studied a large sample of male children from birth to adulthood. The purpose of the study was to determine why some children who are maltreated grow up to develop antisocial behavior and hence have increased probabilities of committing crimes, whereas others do not. The results indicated that MAOA (Monoamine oxidase A) was playing a moderating role. MAOA metabolizes neurotransmitters such as dopamine (DA) and thus moderates human behavior. An experiment, conducted in 1993, first demonstrated the association between MAOA and aggressive behavior in humans. However, since the mutation of the gene is very rare, no one has replicated the results of the report.

Moffitt and Caspi studied 442 males from the sample used by New Zealand’s Dunedin Multidisciplinary Health and Development Study. There was detailed data in all aspects regarding these 442 persons from childhood to twenty-six years of age. Therefore, the data was perfect for the study. Scientists studied the activity of MAOA in these males and their personal development, such as whether they were maltreated in childhood and whether they developed antisocial behavior or had crime records in adulthood. The team discovered that severely maltreated boys were more likely to exhibit antisocial behavior than boys who had suffered little or no abuse.

Secondly, researchers also found that antisocial behavior was more likely in maltreated males with the genotype for low MAOA activity. The MAOA gene is located on the X-chromosome; therefore, males, having only a single X-chromosome, have only one MAOA gene. If genetic mutation takes place in this gene, it will increase the possibility of antisocial behavior. In comparison, females have two MAOA genes because they have two X-chromosomes. So even if one of the genes develops genetic mutation, the possibility of antisocial behavior would still be reduced on account of the protection of the other gene. This may explain why males are more likely to develop aggressive behavior. However, Moffitt found that environmental influences on the role of MAOA gene were critical. That is because the low-activity genotype doesn’t [necessarily] lead maltreated boys to be more likely to be antisocial when they grew up. Jon Beckwith of Harvard Medical School in Boston said, “I would like to use this finding as a wonderful teaching class example to reflect how social factors can play an enormous role in expression of behavioral traits.”

Despite the rapid development in human science and great improvement in material life, endless crimes such as the '9.11' terrorist attack have been damaging the living environment of human beings. Scientists and sociologists hope that studies about human behavior and human genotypes can find the cause of crimes and hence put an end to them. The study on MAOA indicated to us the important role of social and environmental factors in human antisocial behavior. If morality of the whole society could improve, child abuse could be stopped and the possibility of children developing crimes in their later lives could be prevented accordingly. Even if mutation in MAOA happens, it will not lead to their antisocial behavior when they grow up. Therefore, in view of the enormous restricting role of the social factors in human behavioral traits, to enhance human morality and create a caring and loving social environment may well be the key in preventing crimes in human society.

1. Stokstad, E. Violent effects of abuse tied to gene. (2002) Science 297,752.

2. Capsi, A., McClay, J., Moffitt, T.E., Mill, J., Martin, J., Craig, I.M., Taylor, A. and Poulton, R. (2002) Science 297, 851-854.

3. Burnner, H.G., Nelen, M., Breakefield, X.O., Ropers, H.H. and Van Oost, B.A. (1993) Science 262, 578-580.

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