pending and Cochran, 2002; Wang et al., 2004). Our new findings 

 do not contradict this emphasis but may provide one explanation 

 that could have even wider significance. It remains to be seen wheth- 

 er the other 300 genes estimated to show positive selection would 

 also relate to environmental factors. We will be examining additional 

 longitudinal data to test these ideas further. 



Later Childhood 



Gerardi-Caulton (2000) carried out some of the first research link- 

 ing effortful control (EC) to underlying brain networks of executive 

 attention. Executive attention is typically measured in conflict situ- 

 ations such as the Stroop task. Because children of preschool age 

 do not typically read, location and identity rather than word meaning 

 and ink color served as the dimensions in the spatial conflict task. 

 Children sat in front of two response keys, one located to the child's 

 left and one to the right. Each key displayed a picture, and on every 

 trial, a picture identical to one of the pair appeared on either the left 

 or right side of the screen. Children were rewarded for responding 

 to the identity of the stimulus, regardless of its spatial compatibility 

 with the matching response key (Gerardi-Caulton, 2000). 



Reduced accuracy and slowed reaction times for spatially incom- 

 patible trials relative to spatially compatible trials reflected the effort 

 required to resolve conflict between identity and location. Performance 

 on this task produced a clear interference effect in adults and activated 

 the anterior cingulate (Fan et al.. 2003). Children 24 months of age 

 tended to use one response regardless of what was correct, while 36- 

 month-old children performed at high accuracy levels but, like adults, 

 responded more slowly and with reduced accuracy to conflict trials. At 

 3 years of age and older, the time to resolve conflict was negatively 



Fig. 10. Three child temperament scales: (a) Activity level, (b) high-intensity 

 pleasure frisk taking) and (c) impulsivity showing an interaction between parenting 

 in presence or absence of the 7-repeat allele of the DRD4 gene (after Sheese et al., 

 submitted). In the presence of the 7 repeat, parenting quality matters much more to 

 child temperament. 



17 



