Differential parental investment in families with both adopted and genetic children

Reared-apart/reared-together Chinese twins and virtual twins: Evolving research program and general intelligence findings

China's One-Child Policy (1979-2015) limited rural families to two children and urban families to one child. This practice, which led to the abandonment of hundreds of thousands of female infants, is indirectly responsible for the separate placement of infant twins. The availability of this sample launched the first prospective study of these pairs. Participants include families and twins comprising 15 monozygotic (MZA) pairs and 7 dizygotic (DZA) pairs from countries throughout the world. The research program is described, and the initial wave of IQ scores for MZA and DZA twin pairs is examined in the first comprehensive report from this study. The twins' mean age at participation was 9.41 years (SD = 6.36), and their ages ranged from 3.19 to 24.98 years. Informative contrasts with adopted-together Chinese twins and virtual twins (same-age unrelated individuals reared together) highlight shared genetic and environmental effects on intellectual development. Applied directions based on findings from these novel samples are described.

The effect of genetic vs nongenetic parental care on adult children's income and wealth in later life: An evolutionary analysis

OBJECTIVE

Using Wave IV of the National Longitudinal Study of Adolescent to Adult Health data set, this preregistered study set out to investigate the effect of parental care arrangements (eg, genetically related parents, adoptive, step/ foster, genetic nonparental relative, and no parental figure) on adult children's income and wealth in later life.

METHODS

Consistent with the preregistration plan, multivariate analyses of covariance were first used to examine, separately, the effects of paternal and maternal care arrangements on children's income and wealth in later life. Further post hoc exploratory analyses were carried out to evaluate the robustness of the findings.

RESULTS

The results indicate that individual earnings in later life are unrelated to paternal care arrangements, thus questioning a key tenet of kin selection theory. However, children raised by biological fathers and adoptive fathers still enjoy significant economic advantages over nongenetic father figures and homes without fathers in relation to household income and wealth.

CONCLUSIONS

Prevailing theories suggest that children raised by relatives, nongenetically related parents, and no father or mother suffer from a lack of parental investment that should manifest itself in reduced earnings and assets in adulthood. These theories are only partially correct, with evidence pointing to no deleterious effect of variable parental arrangements on individual earnings.

Genetic Relatedness, Emotional Closeness and Physical Aggression: A Comparison of Full and Half Sibling Experiences

Two studies investigated whether perceived closeness of siblings, and aggression between siblings, were associated with genetic relatedness. In following Hamilton's rule, we predicted that as the coefficient of relatedness between siblings increased, emotional closeness would also increase while conflict would decrease. Contrary to the predictions, we found no effect of genetic relatedness in Study 1 when we compared participants' (n = 240) ratings of emotional closeness; participants also reported significantly higher levels of conflict with full siblings than with half siblings. In Study 2, participants (n = 214) also reported a higher frequency of physical aggression with full siblings than with half siblings. These findings were contrary to the prediction from Hamilton's rule. We discuss them in relation to parental investment in biological and non-biological offspring.

Adopted daughters and adopted daughters-in-law in Taiwan: a mortality analysis

Adoption is sometimes considered paradoxical from an evolutionary perspective because the costs spent supporting an adopted child would be better spent on rearing one's own. Kin selection theory is commonly used to solve this paradox, because the adoption of closely related kin contributes to the inclusive fitness of the adoptive parent. In this paper, we perform a novel test of kin selection theory in the context of adoption by asking whether adopted daughters-in-law, who contribute directly (i.e. genealogically) to the perpetuation of their adoptive families' lineages, experience lower mortality than daughters adopted for other purposes in historical Taiwan. We show that both classes of adopted daughter suffer lower mortality than biological daughters, but that the protective effect of adoption is stronger among daughters who were not adopted with the intention of perpetuating the family lineage. We speculate as to the possible benefits of such a pattern and emphasize the need to move beyond typological definitions of adoption to understand the specific costs and benefits involved in different forms of caring for others' children.

If looks could heal: Child health and paternal investment

Data from the first two waves of the Fragile Family and Child Wellbeing study indicate that infants who look like their father at birth are healthier one year later. The reason is such father-child resemblance induces a father to spend more time engaged in positive parenting. An extra day (per month) of time-investment by a typical visiting father enhances child health by just over 10% of a standard deviation. This estimate is not biased by the effect of child health on father-involvement or omitted maternal ability, thereby eliminating endogeneity biases that plague existing studies. The result has implications regarding the role of a father's time in enhancing child health, especially in fragile families.

RELATIVES IN RESIDENCE: RELATEDNESS OF HOUSEHOLD MEMBERS DRIVES SCHOOLING DIFFERENTIALS IN MOZAMBIQUE

Children typically receive investments from their fathers, but absent fathers often invest at low levels. In fathers' absence, what types of non-fathers invest heavily in children? This paper investigates educational participation as a reflection of childhood investments on Ibo Island, Mozambique, where only one third of school-aged children live with their biological fathers. Father-present children generally attended school at the highest rates. Stepchildren and father-absent relatives (e.g. grandchildren, nieces) attended school at comparably high rates if any co-residing children were father-present. This may signal high altruism among present fathers toward some non-offspring. Consistent with this result, a fixed-effects model indicates that, within the same household, adult males invested equally in their own children, relatives, and stepchildren. However, prejudicially lower investments were made in children who were unrelated to the household's adult males; this result has strong negative implications for the wellbeing of African children who are fostered by non-relatives.

Adoption, Foreign-Born Status, and Children's Progress in School

Using recent data from the American Community Survey, the author investigated how the dynamics of immigration influence our understanding of the adoption-schooling relationship. The results suggest that implications of immigrant and adoption statuses could be understood within specific familial contexts. Thus, no statistical differences were found in the outcomes of foreign-born adoptees in U.S. native families and their peers with immigrant parents. Instead, the most favorable patterns of schooling progress were found among U.S.-born adoptees living in immigrant families. Among immigrants, the analysis indicated similar patterns of achievement among Hispanic and White adoptees that are inconsistent with the predictions of segmented assimilation theory. However, there was a Hispanic disadvantage relative to Whites among immigrant children living with biological and stepparents. The article concludes with a discussion of the implications of these findings for kinship selection and assimilation processes and the contention that alternative theoretical frameworks should be used to understand the implications of adoption status.

Adoption Does Not Increase the Risk of Mortality among Taiwanese Girls in a Longitudinal Analysis

Adopted children often experience health and well-being disadvantages compared to biological children remaining in their natal households. The degree of genetic relatedness is thought to mediate the level of parental investment in children, leading to poorer outcomes of biologically unrelated children. We explore whether mortality is related to adoption in a historical Taiwanese population where adoption rarely occurred among kin. Using Cox proportional hazards models in which adoption is included as a time-dependent covariate, we show that adoption of girls does not increase the risk of mortality, as previously suggested; in fact, it is either protective or neutral with respect to mortality. These results suggest that socio-structural variables may produce positive outcomes for adopted children, even compared to biological children who remain in the care of their parents.

Influence of nutrition and lifestyle on bone mineral density in children from adoptive and biological families

Background

The precise contributions of hereditary and environmental factors to bone density are not known. We compared lifestyle predictors of bone density among adopted and biological children.

Methods

The study comprised 18 adopted children (mean [SD] age, 14.0 [4.1] years) with their non-biological parents and 17 children with their biological parents. Bone mineral density (BMD; g/cm²) was measured at the lumbar spine, total femur, and distal radius. Nutritional intake was assessed by food frequency questionnaire. Information on smoking and physical activity was obtained by questionnaire.

Results

Intakes of all nutrients, corrected for energy intake, and all lifestyle characteristics except sleep duration were similar in biological children and their parents. As compared with their parents, adopted children had significantly different energy, protein, and calcium intakes and physical activity levels. In a regression model, BMD z scores of adopted children and their parents were significantly inversely associated at the spine and total femur, whereas BMD z scores of biological children and their parents were significantly positively associated at all measurement sites. The greatest proportion of total variance in BMD was accounted for by calcium intake among adopted children and by parental BMD among biological children.

Conclusions

For some lifestyle characteristics and nutrient intakes, the differences between parents and children were more obvious among adoptive families than among biological families. The most important lifestyle predictor of bone density was calcium intake.

Genetic and adoptive motherhood: stress, marital relationship, and child care support

In this paper we characterize adoptive and genetic motherhood with or without stress indicators. Participants were 86 mothers (36 adoptive, 50 genetic) with children from 0 to 12 years old. They answered questions about focal child and mother profile, marital relationship, child care support and the Lipp's Stress Symptoms Inventory for Adults. Results showed that mothers in both groups reported child care support, but there was more participation of nonrelatives in the care of adoptive children and relatives in the care of genetic children. There was greater marital stability and less conflict with the arrival of the child in the adoptive families and predominance of stress indicators in genetic mothers. We concluded that, although there are differences between adoptive and genetic motherhood, these do not imply advantages for one versus the other. Moreover, marital stability related to the adoption process and sociodemographic characteristics of adoptive mothers may have contributed to lower prevalence of stress.

The puzzle of monogamous marriage

The anthropological record indicates that approximately 85 per cent of human societies have permitted men to have more than one wife (polygynous marriage), and both empirical and evolutionary considerations suggest that large absolute differences in wealth should favour more polygynous marriages. Yet, monogamous marriage has spread across Europe, and more recently across the globe, even as absolute wealth differences have expanded. Here, we develop and explore the hypothesis that the norms and institutions that compose the modern package of monogamous marriage have been favoured by cultural evolution because of their group-beneficial effects-promoting success in inter-group competition. In suppressing intrasexual competition and reducing the size of the pool of unmarried men, normative monogamy reduces crime rates, including rape, murder, assault, robbery and fraud, as well as decreasing personal abuses. By assuaging the competition for younger brides, normative monogamy decreases (i) the spousal age gap, (ii) fertility, and (iii) gender inequality. By shifting male efforts from seeking wives to paternal investment, normative monogamy increases savings, child investment and economic productivity. By increasing the relatedness within households, normative monogamy reduces intra-household conflict, leading to lower rates of child neglect, abuse, accidental death and homicide. These predictions are tested using converging lines of evidence from across the human sciences.

Adoptive parents' suspicion of preadoption abuse of their adopted children and the use of support services

BACKGROUND

Adopted children have a higher risk of developmental, mental, behavioural and social problems compared with non-adopted children, and their use of postadoption support services is of interest. Little attention has been given to the impact of preadoption abuse on the use of these services, and therefore this study examines whether or not adoptive parents' suspicion of preadoption abuse has a significant impact on the use of support services by adopted children.

METHODS

Data from the National Survey of Adoptive Parents, a US nationally representative survey of adopted children, were used to examine parents' suspicion of preadoption abuse and its effects on the use of postadoption support services by children aged 6-17 years (n = 1411). Statistical analyses were used to examine the relationship between suspected abuse and the use of support services while controlling for characteristics of the adopted child and adoptive parents/household.

RESULTS

Seven out of 10 adopted children have used some form of support service, and a larger percentage of 6- to 12-year-old children suspected of experiencing preadoption abuse used a support service compared with children not suspected of experiencing abuse. Significant relationships existed between various types of suspected preadoption abuse and the use of different types of postadoption support services. These relationships may go unaccounted for when only examining if any preadoption abuse occurred, or if any support service was used.

CONCLUSIONS

The type of preadoption abuse suspected appears to play a modest role in predicting the type of postadoption support services used by an adopted child. Giving further attention to understanding the relationship between different types of preadoption abuse and types of postadoption support services may help better understand the problems and difficulties experienced by adopted children.

Review: Adoption research: Trends, topics, outcomes

The current article provides a review of adoption research since its inception as a field of study. Three historical trends in adoption research are identified: the first focusing on risk in adoption and identifying adoptee—nonadoptee differences in adjustment; the second examining the capacity of adopted children to recover from early adversity; and the third focusing on biological, psychosocial, and contextual factors and processes underlying variability in adopted children’s adjustment. Suggestions for future areas of empirical investigation are offered, with an emphasis on the need to integrate research, policy, and practice.