A Gene-Environment Interaction in Antisocial Behavior?
"Role of Genotype in the Cycle of Violence
in Maltreated Children"
(Science, 2 August 2002)
David C. Rowe and Judith Rich Harris
Maltreatment of children is rightly condemned as brutal and
harmful. However, the study by Caspi et al.  of the MAOA gene
does not prove a causal connection between abuse in childhood
and antisocial behavior in adulthood, because their research
design for abuse was correlational.
As Caspi et al. reported, not all abused children become
antisocial adults. Nor do all siblings become antisocial in a
family in which abuse has occurred . These findings suggest
a possible role for other genes -- a gene x gene interaction,
rather than the gene x environment interaction proposed by
Caspi et al. The other gene or genes, present in the parents
as well as the children (because children inherit their genes
from their parents), might predispose the parents to behave
abusively and, in conjunction with the low-MAOA allele, might
increase the risk that the children will become antisocial.
Another possibility is that an environmental correlate of child
abuse might be responsible for the interaction reported by
Caspi et al. . For example, abused children are often removed
from their homes and are sometimes moved around repeatedly.
The resulting disruption of their lives, rather than the abuse
per se, could be the triggering environmental factor that
predisposes children with the low-MAOA allele to become antisocial.
These observations are meant to clarify, rather than detract from,
the pioneering contribution of Caspi et al. Their use of measured
genotypes will make hypotheses testable that were previously not
even on the table.
David C. Rowe
Division of Family Studies and Human Development &
Graduate Interdisciplinary Program in Genetics
University of Arizona
Judith Rich Harris
Middletown, New Jersey
Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W.,
Taylor, A., & Poulton, R. (2002, August 2).
Role of genotype in the cycle of violence in maltreated children.
Science, 297, 851-854.
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The Nurture Assumption. New York: Free Press.