What is the hypothesis in the following?

Genetic factors are important for the ociation between parental negativity and child problem behavior, but it is not clear whether this is due to pive or evocative genotype–environment correlation (rGE). In this study, we applied the extended children-of-twins model to directly examine the presence of pive and evocative rGE as well as direct environmental effects in the association between parental criticism and adolescent externalizing problem behavior. The cross-sectional data come from the Twin and Offspring Study in Sweden (N = 909 pairs of adult twins) and from the Twin Study of Child and Adolescent Development (N = 915 pairs of twin children). The results revealed that maternal criticism was primarily due to evocative rGE emanating from their adolescent's externalizing behavior. On the other hand, fathers' critical remarks tended to affect adolescent problem behavior in a direct environmental way. This suggests that previously reported differences in caretaking between mothers and fathers also are reflected in differences in why parenting is associated with externalizing behavior in offspring. (PsycINFO Database Record (c) 2011 APA, all rights reserved) (from the journal abstract)