• By Dartington SRU
  • Posted on Thursday 13th August, 2009

Too many short-gene kids on the block?

Abnormal aggression among young people has been attributed to causes as diverse as television, music, social inequality and the structure of the human genome - it is clear that narrow theories fall woefully short. The more useful research tendency is to combine sociological studies of neighborhoods with genetic research, witness a recent study by a team from Rutgers University in New Jersey.And their cross-disciplinary findings have persuaded them that there is a potentially damaging social condition they call “high child saturation”. In neighborhoods where the proportion of children is high, young people are likely to become more aggressive; high percentages of children are more common among deprived neighborhoods.Published in Development and Psychopathology, the study looked at data from the National Longitudinal Study of Adolescent Health which charted the progress of more than 17,000 children over the course of a year. It turned out that the effect of high child saturation on children was not just long term. When information on children who had moved neighborhood over the course of the year was analyzed separately, it showed that those who moved to areas of higher saturation soon became more aggressive. It took less than a year for the change to to have a significant impact. But the study was not only concerned with the influence of the broader environment. A team from the Institute of Behavioral Genetics at the University of Colorado tested a sub-sample of 900 children for variations in their MAOA gene. The gene is thought to influence people’s sensitivity to social pressure. Children with the “short” version are inclined to seek the approval of others; those with the “long” adaptation are less likely to do so. When these data were matched up with the information on child saturation a strong pattern emerged. Young people with the short MAOA gene, and so considered to be more susceptible to social pressure, were more likely to show increases in aggression if they were living in neighborhoods where there was high child saturation. Aggression levels among those with the long version of the gene did not vary across neighborhoods. Supposedly sensitive to social rejection, children with the short MAOA gene usually conform to what is expected of them and are well behaved. “In an environment with many youths relative to adults, there are fewer adults to make and enforce rules, and more more youth to model aggressive behavior,” the authors explain. In those circumstances, violence can appear quite normal and acceptable.The authors draw an analogy from the work of Boyce and Ellis who described how certain genetic traits can be a strength in one context but a liability in another. Those who are heavily influenced, who flourish in low stress environments, but fare poorly in less supportive conditions they called "orchids". Those less likely to prosper in supportive conditions, but who are resilient to high risk environments, they called less reactive “dandelions”. Many previous studies of antisocial behavior have looked at the interaction between genes and family, but few have examined how children’s genetic inheritance relates to wider environmental factors.“It is possible that an understanding of the broad social context, of which neighborhoods are one part, can contribute to a more nuanced understanding of the emergence of aggression,” the authors write. See: Hart D and Marmorstein N R (2009), "Neighborhoods and genes and everything in between: Understanding adolescent aggression in social and biological contexts," Development and Psychopathology, 21, 3, pp. 961-973Boyce W T and Ellis B J (2005), “Biological sensitivity to context: I. An evolutionary–developmental theory of the origins and functions of stress reactivity,”, Development and Psychopathology, 17, 2, pp. 271-301.

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