A noteworthy point here is that whilst a heritable environmental variable is indicative of rGE, it has been argued that for parenting measures in child-based twin samples (such as G1219) passive rGE is actually more likely to load onto C than A (Neiderhiser et al. 2004; Rijsdijk and Sham 2002). This is because in passive rGE the genotype of the parent influences the way that the parent treats their child, independent of the characteristics of the child. As such this is likely to result in parenting that is similar across siblings and does not vary by the genetic relatedness of the siblings (i.e. MZs vs. DZs). We would add that this logic perhaps applies to parent-report parenting in child twin samples more than it does to child-report parenting, as child-report parenting will also be affected by children’s genes. Regardless, it may be more likely that in child twin samples such as ours heritable parenting measures are more indicative of non-passive rGE than passive rGE. That said, in the current study it was not possible to definitively distinguish between types of
