Abstract
This paper advises caution in relation to the increasing interest in molecular-genetic association studies in developmental psychology based on a set of empirical examples from the NICHD Study of Early Child Care and Youth Development (SECCYD) that highlight the fragility of effects reported in the literature on the molecular-genetic correlates of infant attachment. Specifically, this paper updates and provides three extensions to results reported in Luijk et al. (2011), which recently failed to replicate evidence from smaller-sample studies that a set of dopaminergic, serotonergic, and oxytonergic markers are significantly associated with infant attachment security or disorganization. First, we report here that the average effect of "usual suspect" polymorphisms on infant attachment security and disorganization in the SECCYD is approximately zero. Second, because Luijk et al. (2011) reported data based exclusively on the White infants in the SECCYD, this paper reveals that the average effect of polymorphisms featured in this literature is also of trivial magnitude in the non-White sub-sample (cf. Chen, Barth, Johnson, Gotlib, & Johnson, 2011). Third, this paper attempts, but fails, to replicate a recent finding by Raby et al. (2012) suggesting that, although molecular-genetic polymorphisms might not be implicated in security versus insecurity, the serotonin transporter gene contributes to variation in emotional distress during the Strange Situation Procedure. Implications for future research on the genetics of developmental phenotypes in general and attachment in particular are discussed, with a focus on statistical power and model-based theory testing.