, 2002). It is now widely believed that vulnerability to bad behavior is conditional and depends on genetic susceptibility (Kendler, 2001; Rutter & Silberg 2001; in Caspi et al., 2002).
This theory was tested by Caspi et al. (2001) when they attempted to predict antisocial behavior among more than 1000 male maltreated children by genotyping their polymorphism at the MAOA gene. Their findings provided epidemiological evidence that high MAOA expression moderates the effect of maltreatment and partially explained why not all victims of maltreatment grow up to retaliate by victimizing others (Caspi et al., 2001). In this case, genotype (polymorphism at the MAOA gene) is shown to moderate children's sensitivity to environmental insults (maltreatment).
Having said that there are certain characteristics where genes play a moderation role to the environment, the opposite can also be true. One of these characteristics is cognitive ability among children. It is widely accepted that cognitive and academic outcomes like IQ can be predicted by environmental factors such as socio-economic status or SES (Friend, DeFries, & Olson, 2008). One measure of SES is parental education, which gives an indication of the level of investment in a child's education and performance in school (Craig, 2006, in Friend, DeFries, & Olson, 2008). Parents who are highly educated tend to have the resources to create an environment that enhances learning among their children. For children who develop learning disabilities despite a nurturing environment, the bioecological model of GXE of interaction is proposed; that is, genetic influences on behavior should be most evident when the environment is supportive (Ceci, 1994, in Friend, DeFries, & Olson, 2008).
In a study of more than 500 identical and fraternal twins, it was found that on average, the heritability of reading disability (the most common form of learning disability) was more a function of genes rather than environment among children whose parents had a higher level of education, compared to those whose parents had a lower level of education (Friend, DeFries, & Olson, 2008). In other words, children who failed in reading despite having a nurturing environment tended to have stronger genetic influences on their...
What is interesting is that these practices can actually act as stimuli that influence the expression of hormones responsible for certain behaviors. A recent study of 185 mother-infant tandems showed that maternal care giving behavior (MCB) could change the expression of hormones that regulate responses to new environments or situations among infants (Hane and Fox, 2006). In this study, it is demonstrated that infants who received low-quality MCB are more stress reactive -- showing fearfulness, less positive joint attention to a shared object, and low sociability -- in a new environment compared to those who received high -quality MCB. In another aspect of the study, in their natural home environments, those infants characterized as stress-reactive are inherently more distressed and prone to crying than the infants in the high MCB group. This observation prompted the investigators to surmise that the infants' temperament influence the mother-child relationship (Hane and Fox, 2006). Hence, this study not only demonstrates gene-environment interaction but also gene-environment correlation -- innate infant behavior altering the quality of maternal behavior - in child development.
Some adoption design studies portray similar GXE correlations. Research shows that adopted kids whose biological parents have a history of substance abuse/personality disorders are more likely to show problematic behavior such as lack of self-control and being antisocial compared to those adopted kids with untroubled biological parents (Ge et al., 1996 in Shakoff and Philips, 2000). More often than not, these behaviors in turn result in harshness and less nurturing from the adoptive parents. Hence, inherited characteristics can invoke complementary treatment from parents (Shakoff and Philips, 2000).
Contemporary views on nature-nurture interactions, as justified by molecular and behavioral genetics studies, only reiterate the complex and dynamic relationship between genes and environment in the actualization…
