An Evolutionary Perspective on Parental and Grandparental Investment

Although great effort has been spent on studying the effects of parenting on child development, much less research has focused on factors that predict individual differences in parental investment. In this dissertation, an evolutionary psychological perspective was used to identify characteristics in children that stimulate their parents and grandparents into giving them the care, attention, and emotional support they need. From an evolutionary perspective, parental investment is a means of optimizing the reproductive success of the parent. Parental investment was defined by Trivers (1972) as “any investment by the parent in an individual offspring that increases the offspring’s chance of surviving (and hence reproductive success) at the cost of the parent’s ability to invest in other offspring”. So defined, parental investment is limited, and parents have to make decisions on how to allocate their resources among their offspring. According to evolutionary theory, parents are not expected to invest equally in each of the children in their household. Instead, parents are expected to favor children on the basis of their genetic relatedness and reproductive value (i.e., the child’s probable future reproductive success). In this dissertation we examined whether possible cues of genetic relatedness (i.e., parent-child resemblance and olfactory recognition) and reproductive value of the child (i.e., child attractiveness and facial symmetry) were related to parental investment in a sample of Dutch parents with school-age children. The results of our study indicate that mothers had a closer bond and spent more time with children who resembled them in personality, whereas fathers had a closer bond and used less punishment with children who resembled them physically. In addition, the ability to recognize one’s children by smell was associated with an increase in time investment for fathers, and an increase in emotional closeness and a decrease in punishment for mothers. Furthermore, both mothers and fathers reported having a closer bond with more attractive children, and fathers punished attractive children less often. Thus, despite the fact that in a contemporary Western society, such as the Netherlands, families are relatively small and emotional and economic resources are more than enough for parents to invest equally in all of the children in their household, our results suggest that parental investment by both mothers and fathers is still influenced by cues of both genetic relatedness and reproductive value of the child. In addition to individual differences in parental investment we examined differential investment by grandparents. Even though grandparental care positively influences the grandchild’s health and well-being, and thus contributes to grandparental lifetime reproductive success, not all grandparents invest equally in their grandchildren. We examined whether these differences in grandparental investment can be explained by certainty of relatedness (as assessed by kinship lines). The quality of the grandparent-grandchild relationship was rated highest with maternal grandmothers (most genetically certain) and lowest with paternal grandfathers (least genetically certain). Relationship quality with both maternal grandfathers and paternal grandmothers was rated as intermediate. These results are consistent with the prediction that discriminative grandparental solicitude varies as a function of certainty of relatedness.