typed the children for several candidate genes including the DRD4 

 gene that had been related to ADHD and sensation seeking (see 

 above). 



One finding with the DRD4 gene (Sheese et al., 2007) seems to 

 have important implications beyond the study of one particular mol- 

 ecule. We found, as shown in figure 10, that in the presence of the 

 7-repeat allele, there was a strong influence of parental quality. Par- 

 ents who were rated as giving greater support, autonomy etc., had 

 children that were average in a reported aggregate we called sen- 

 sation seeking, consisting of activity level, impulsivity, and risk tak- 

 ing. Children given somewhat lower-quality parenting, however, 

 showed extremely high levels of sensation seeking. For children 

 without the 7 repeat, parental quality did not have a significant in- 

 fluence. Our sensation-seeking aggregate comes from caregiver re- 

 ports on their child's temperament, but its constituents are similar 

 to symptoms frequently reported by children with ADHD. Thus we 

 think that the paradox of the 7 repeat may arise because its presence 

 can produce symptoms of ADHD without attention deficits, but its 

 presence does not automatically lead to later problems; that depends 

 upon environmental influences such as parenting. Similar evidence 

 that environment can have a stronger influence in the presence of 

 the 7 repeat has been reported by others (Bakermans-Kranenburg 

 and van Ijzendoorn, 2006; van Ijzendoorn and Bakermans-Kranen- 

 burg, 2006). 



Positive selection of the 7-repeat allele could well arise from the 

 sensitivity to environmental influences that it may help to make 

 possible. Parenting allows the culture to train children in the values 

 that it favors. For example, Rothbart and colleagues (Ahadi et al., 

 1993) found that in Western culture effortful control appears to reg- 

 ulate negative affect (sadness and anger), while in China (at least in 

 the 1980s) it was found to regulate positive affect (outgoingness and 

 enthusiasm). In recent years the nature/nurture interaction has tilted 

 very much to the importance of genes, but if genetic variations are 

 selected according to their influence on the sensitivity of the child 

 to cultural influences, this could support a balance between genes 

 and environment. Theories of positive selection in the DRD4 gene 

 have stressed the role of sensation seeking in human evolution (Har- 



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