Theoretical Perspectives on Children’s Sibling Relationships in Stepfamilies
Although multiple theories are proposed to explain sibling ties and sibling effects on each other in stepfamilies, in general these theories revolve around two primary foci: (1) parental resources and parental investments in children, and (2) family stress and instability due to sibling structure. In addition, a few scholars have investigated selection effects as well, but this is less a theory than an explanation for differences between different types of sibling relationships or between stepfamilies with different sibling structures.
Parental Resources and Investments
The primary argument in the parental resource/investment theoretical perspective is that parents and stepparents have limited resources (e.g., abilities, time, money) to invest in children, and the presence and number of other children, and the type of relationships among the children in the family affect how and upon which child parents and stepparents invest their resources (e.g., Strow & Strow, 2008). As a corollary of this perspective, the resource dilution effect simply states that the more children there are, the more parental resources are diluted, and the less each child will receive (Bobbitt-Zeher & Downey, 2012) . Gennetian (2005) , employing a resource model, likened mutual children of a stepfamily couple, or of any couple, to a “public good” in that pouring resources into the child’s development is seen as a benefit to all. Stepchildren, belonging to only one of the adults in the stepfamily, are seen as a “private good,” leading to different, and lower, allocations of resources to stepchildren than to the mutual children of the step-couple.
Evolutionary scholars expect parents to invest more resources in rearing biologically related children than stepchildren (Schlomer, Ellis, & Garber, 2010) . For instance, parent-offspring conflict theory (POCT) states that parents, who are genetically related (50 %) equally to all of their genetic offspring, will attempt to invest their resources equally among them. Children, on the other hand, are more invested in their own fitness (they are 100 % related to themselves) than they are to siblings (50 % related), and so children are expected to compete with each other for scarce parental resources (Schlomer et al., 2010) . Fewer parental resources or increased demands on resources, such as when children are added to the family, enhance sibling competition. POCT further states that in families in which there are both half-siblings and stepsiblings, parental resources will be less evenly distributed to children (a stepparent is 0 % genetically related to stepchildren; children are 25 % related to half-siblings, 0 % to stepsiblings), which engenders more competition and conflicts between offspring and parents.