In the past, a dominant assumption in the childrearing literature has been that the relationship between children and their environment is unidirectional – that environments shape children. Nonetheless, a minority of developmental theorists has noted the need to consider the possibility that children both shape their environments and are influenced by them (e.g. Bell, 1968
; Brofenbrenner 1986
). This is true of the parenting that children receive, in particular. Bell (1968)
suggested that parents do not have fixed parenting techniques, but rather a repertoire of potential actions. Activation of elements in the repertoire requires both cultural pressures and stimulation from the object of acculturation. Brofenbrenner (1986)
similarly emphasized that parenting behavior is influenced by both proximal and distal influences in parents’ histories and environments as well as children’s evocative behavior.
In particular, several theorists have proposed a role of children’s evocative qualities in the etiology of childhood maltreatment (Belsky, 1993
; Steele, 1980
; Vasta, 1982
). They argued that maltreatment is associated with a combination of parent characteristics (such as their personality, psychological resources, their own abuse history, and unreasonable expectations for children), child characteristics (such as their age, health, disruptive behaviors, prematurity, developmental difficulties, and retardation), and community/cultural characteristics (such as shared values, the availability of social support, and stressors such as unemployment and marital instability). The role of these hypothesized child effects on maltreatment has been minimized in the relevant literature despite an absence of evidence suggesting a lack of child effects. This may be due to a fear that evidence of variance in maltreatment associated with child characteristics (i.e. child effects) would erroneously be interpreted as suggesting that maltreatment is children’s fault. In reality, however, evidence of child effects would merely document that there are qualities in children that raise the probability that caregivers will maltreat them.
Evidence garnered from a variety of methods converges to demonstrate that children can shape the parenting they receive. An early indication came from observation of a mother who responded differently to two children she adopted simultaneously of the same age and gender (Yarrow, 1963
). In a laboratory study, mothers of conduct disordered boys as well as mothers of non-conduct disordered boys reacted more negatively when interacting with unrelated conduct disordered boys than when interacting with unrelated non-conduct disordered boys (Anderson, Lytton, & Romney, 1986
). In another laboratory study, the level of dependency girls were manipulated to display positively predicted how interactive and controlling parents behaved toward them (Osofsky & O’Connell, 1972
Further evidence that children influence the parenting they receive comes from twin and adoption studies of putatively environmental influences. Recently, Kendler and Baker (2007)
conducted a review of 55 independent studies examining the magnitude of genetic influences on putatively environmental constructs such as stressful life events, parenting behavior, family environment, and peer interactions and found a mean heritability of 27%. Such evidence of genetic influences on constructs usually thought of as environmental is evidence of gene-environment correlation, or genetic variance among children being correlated with individual differences in their experiences.
There are three types of gene-environment correlations: evocative, active, and passive (Neiderhiser et al., 2004
; Plomin, DeFries, & Loehlin, 1977
). Evocative gene-environment correlations occur when genetically influenced characteristics of children evoke responses from the environment. For example, genetically influenced disruptive behaviors may provoke caregivers to maltreat them. Active gene-environment correlations occur when a child selects environments that are correlated with his or her genetically influenced characteristics. For example, a child with high genetic proclivity towards reading may choose to spend time in environments in which books are available, such as libraries. Although evocative and active gene environment correlations are fundamentally different processes, both indicate a correlation between children’s genes and their environmental experiences and are indistinguishable in a twin study (Neiderhiser et al., 2004
); therefore, they are considered together as nonpassive
gene-environment correlations in the present study. In contrast, passive gene-environment correlations arise because parents’ genes are correlated with both the environment they create for their children and their children’s genes. For example, parents with a genetic vulnerability to antisocial behavior may maltreat their children and also pass on genetic vulnerability to antisocial behavior to their children; their children’s genetic vulnerability to antisocial behavior and their experience of maltreatment could be positively correlated, but without one directly causing the other.
Researchers conduct twin studies to examine the relative magnitude of genetic and environmental influences on phenotypes of interest. Twin studies take advantage of the fact that both monozygotic (MZ) and dizygotic (DZ) twin pairs are born into the same family at the same time, yet they share different proportions of their genes (100% in MZs and 50% on average in DZs). The twin study allows researchers to partition the variance of a phenotype into those explained by three influences: genetic influences (A), which reflect differences in the similarity of MZ and DZ twin pairs, shared environmental influences (C), which reflect familial correlation not due to genetic factors, and nonshared environmental influences (E), which reflect differences between twins not due to genetic factors.
In a study of genetic variance in mothering, Neiderhiser et al. (2004)
described how univariate behavior genetic analyses of parenting variables are used to test for the presence of passive or nonpassive gene-environment correlation and how the interpretations of the three factors (i.e., A, C, and E) must be modified to account for the possibility of passive gene-environment correlation. Evidence of genetic influences on child-reported parenting means that MZ twin pairs, who share 100% genetic similarity, are reporting more similar parenting experiences than DZ twin pairs, who on average share 50% genetic similarity. A, the genetic factor, captures variance in parenting behavior due to genetically influenced characteristics of children (i.e., genetically influenced child effects/nonpassive gene-environment correlation). Importantly, this design does not include a test of which specific child characteristics mediate the relationship between children’s genetics and the measured variable. C, the “shared environmental” factor, captures the extent to which parents treat their children similarly regardless of whether they are MZ or DZ twins. Although C includes any environmentally mediated similarities in parenting across siblings, it also includes the effect of any passive gene-environment correlation, or the parents’ genetic influences that make them more likely to treat two children similarly regardless of the children’s genetic similarity (i.e., whether they are MZ or DZ twins). In studies including both twins and ordinary full siblings, an additional shared environmental factor, T, may be invoked to capture the increased environmental similarity of twins compared to ordinary full siblings; unlike twins, full siblings are different ages, born at different times, and, possibly, in different parental or other family circumstances. Although C and T may include parent effects on maltreatment, they may also reflect child effects; they may reflect stressors that influence both parents and children that are shared by sibling/twin pairs, such as deviant peers, neighborhood influences, and school influences. E, the nonshared environmental factor, includes any environmentally mediated differences in parenting that may be mediated by the child’s behavior or reflect idiosyncratic parenting behavior) and measurement error.
Genetically uninformative longitudinal designs have been used to demonstrate interactive, coercive cycles between parents and children in which children’s aggressive behavior elicit assertive or coercive parenting, which in turn elicits aggressive behavior in the children, thereby perpetuating a cycle (e.g. Patterson, Bank, & Stoolmiller, 1990
). In these studies, the extent to which children’s behavior is a precursor to or consequence of parenting is unclear. A strength of the genetically informative study of parenting is that a demonstration of genetically mediated child effects on parenting is clear evidence that children bring their own qualities to the interaction beyond that which is shaped by caregivers. It is important to note, however, that genetic effects are not, as they are often misinterpreted to be, immutable. Rather, genes contribute to a child’s vulnerability to or probability of demonstrating a particular behavior, as do environmental influences. A weakness of the behavior genetic study of parenting is that the magnitude of environmentally mediated child effects cannot be directly estimated, given that environmental influences on parenting may be child or parent effects. Therefore, total child effects on parenting may be greater than the genetically mediated child effects.
Twin and adoption studies have been applied to parenting in order to assess the extent to which children’s genetics influence the parenting they receive. Of the behavior genetic studies of putatively environmental influences reviewed by Kendler and Baker (2007)
, 12 examined parenting (e.g., negativity, warmth, control, protectiveness). On average, approximately one quarter of the variance in parenting was attributed to children’s genetic influences, but there was variability in the results. The authors noted that measures of positive emotional quality of the parent-child relationship were more heritable than measures of discipline styles; studies of parental warmth showed the greatest heritability (34%–37%), followed by studies of protectiveness (20%–26%), then by studies of control and negativity (12–17%). The authors inferred that positive emotionality in parent-child relationships may be strongly influenced by genetically influenced temperament. In contrast, parents may learn disciplinary styles during their life experiences, and attempt to apply these styles equally to all their children. Therefore, although theories regarding the etiology of physical maltreatment and neglect reviewed above (e.g., Belsky, 1993
; Steele, 1980
; Vasta, 1982
) suggest that the magnitude of child effects is nontrivial, Kendler and Baker’s (2007)
results suggest that the influence of children’s genetics on maltreatment may be small.
We know of only two studies examining genetically mediated child effects on measures closely related to childhood maltreatment. A study of Caucasian female twins drawn from the large, population-based Virginia Twin Registry (Wade & Kendler, 2000
) examined genetically mediated child effects on both retrospective child- and parent- reported physical discipline occurring before age 17. Consistent with results of prior research, (Achenbach, McConaughy, & Howell, 1987
; Plomin, DeFries, & Loehlin, 1994
; Simonoff, Pickles, Hewitt, & Silberg, 1995
), parents’ reports of parenting were more similar across siblings than children’s reports of parenting. For parent report of physical discipline, genetically mediated child effects accounted for 9–21%, and the “shared environment” accounted for 62–72% of the variance. In contrast, for child report of physical discipline, genetically mediated child effects accounted for 33–40%, and the “shared environment” accounted for 21–28% of the variance. The authors speculated that the difference in results across reporters may reflect a combination of three processes. First, the parent report results may reflect a desirability bias, i.e., it may be desirable for parents to report treating their children equally. Second, parents may be reporting general discipline strategies more so than actual behavior. Third, children may be highly sensitive to perceived differences in how they are treated. In addition, any rater bias (or the tendency to overrate or underrate physical discipline for both twins) on the part of parents would inflate estimates of C (Hewitt, Silberg, Neale, & Eaves, 1992
). In contrast, measurement error in one child’s report is likely to be uncorrelated with measurement error in the other twin’s report, increasing E and decreasing A and C.
Jaffee and colleagues (Jaffee, Caspi, Moffitt, & Taylor, 2004
) examined the genetic and environmental influences on physical maltreatment sufficient to injure a child and on corporal punishment via
a maternal-report twin study conducted when the twins were 5 years old. Genetically-mediated child effects/nonpassive gene-environment correlation accounted for 25% of the variance of corporal punishment. In contrast, nonpassive gene-environment correlation accounted for 0–7% of the variance in physical maltreatment and shared environmental influences that may include passive gene-environment correlation accounted for 94% of the variance. The authors concluded that difficult children may provoke corporal punishment, but factors causing physical maltreatment are more likely to be found within the caregiver or family environment. However, Wade and Kendler’s results suggest that the magnitude of shared environmental influences may have been overestimated in the Jaffee et al. study. Mothers reported that their children experienced extremely similar levels of physical maltreatment, which may reflect reporting bias that over-estimates the magnitude of the shared environment (Hewitt et al., 1992
). Alternatively, the use of a severe threshold in the operational definition of physical maltreatment (i.e., injury) may have captured behaviors that are less likely to be responses to children’s behavior.
The present study examined the etiology of three forms of maltreatment (physical maltreatment, neglect, and sexual maltreatment) reported by the child. We know of no research examining genetically-mediated child effects on neglect or sexual maltreatment. Hypotheses and research regarding child effects on maltreatment have focused primarily on physical maltreatment. However, it is possible that the same child characteristics that frustrate parents and lead to parental anger and withdrawal may be expressed as either physical maltreatment or withdrawal of parental attention and care. Also, both physical maltreatment and neglect may reflect negative aspects of the parent-child relationship that may involve parents’ learned beliefs about acceptable ways to treat children. We are not aware of hypotheses about child effects on sexual maltreatment, and it is difficult to imagine what genetically influenced child qualities would be associated with sexual maltreatment.
Further, although it is well established that diverse types of maltreatment toed to co-occur (e.g. Dong et al., 2004
), we know of no studies testing whether the genetic and environmental influences on one form of maltreatment are shared with the influences on another form. In the present study, multivariate analyses were conducted to examine the degree to which the covariation among different forms of maltreatment is due to common genetically mediated child effects, common shared environmental influences (which may include passive gene-environment correlation), or common nonshared environmental influences.