Genetics of parenting: The power of the dark side.

Genetics of Parenting

Behavioral genetic studies of parenting are informative since they offer unique insights into the contributions of parent and child characteristics; the twin design can be useful in this context, comparing identical, or monozygotic (MZ), and fraternal, or dizygotic (DZ), twins. So-called parent-based twin designs compare the parenting behaviors of twin parents, with the premise that to the extent that parenting behaviors shown by MZ twin parents toward their offspring are more similar than those shown by DZ twin parents, genetically influenced parental characteristics are implicated. A child-based study, like the current one, has twin children as the focus for analyses. Here, the extent to which MZ twins are similarly parented compared with DZ twins is evidence of significant genetic influence on aspects of parenting but suggests that parental behavior reflects genetically influenced characteristics of the child, such as their temperament.

Parental Feelings and Control

Subsequent theoretical and empirical perspectives on parenting have remained largely founded in Baumrind’s earlier work on parenting styles, which at its core, focused attention on two key aspects of parenting—responsiveness/warmth and demandingness/control ( Baumrind, 1973 ). While researchers have distinguished aspects of parenting further, most notably in the area of parental control (e.g., Barber & Harmon, 2002 ) and have varied in their construct labels, these two broad dimensions have been endorsed through numerous studies that have sought to characterize them (e.g., Barber, Stolz, & Olsen, 2005 ; Cummings, Davies, & Campbell, 2000 ; Dodge, Pettit, & Bates, 1994 ; Maccoby & Martin, 1983 ; Rothbaum & Weisz, 1994 ). Here, we have conceptualized these parenting dimensions as parental feelings (warmth, closeness, hostility, frustration) and parental control (discipline strategies such as remaining firm and the use of physical discipline); these dimensions have shown robust modest to moderate associations to children’s outcomes (e.g., Parke & Buriel, 2006 ).

Reviews of behavioral genetic studies have noted that control aspects of parenting tend to yield low estimates of heritability while parental feelings yield moderate estimates ( Kendler & Baker, 2007 ; Plomin, 1994 ; Rowe, 1981 , 1983 ). To be clear, in child-based studies, these findings suggest that genetically influenced child characteristics may be more important for eliciting parental feelings than control. However, research has seldom distinguished between positive and negative parental feelings and particularly between positive and negative control strategies. Blurring the positive and negative sides of feelings and control may mask important underlying foundations of parenting. Harsh discipline and effective supervision, for example, may not be opposite ends of a single continuum, and neither may hostility and warmth (see Pettit & Arsiwalla, 2008 ). Thus, we hypothesized that the underlying genetic architecture of these aspects of parenting may also be distinct. Specifically, following existing relevant family research (e.g., Kendler & Baker, 2007 ; Rasbash, Jenkins, O’Connor, Tackett, & Reiss, 2011 ) as well as work outside the field (e.g., Baker, Cesa, Gatz, & Mellins, 1992 ; Baumeister, Bratslavsky, Finkenauer, & Vohs, 2001 ), we predicted that negativity would show greater heritability than positivity across parental feelings and control as well as within parental feelings and within control.

For the first time in a large-scale, longitudinal, child-based twin study, we explicitly compared the genetic and environmental etiology of positivity and negativity, positive and negative feelings, and positive and negative control.

Measures

We generated eight scales from identical parent-report measures at child ages 9, 12, and 14 years of parental feelings and control. For feelings, we used an adapted short form (seven items) of the Parental Feelings Questionnaire (PFQ; Deater-Deckard, 2000 ) and for control, a short (four-item) discipline (parenting strategies) questionnaire adapted from Deater-Deckard, Dodge, Bates, and Pettit (1998) . Item responses were rarely/never (0), sometimes (1), and often (2), and coding was reversed for items as necessary. Two standard composite measures were created at each age from the PFQ and Discipline questionnaires: Feelings from seven PFQ items, including the three positive (e.g., “I feel close to my child”) and four negative items (e.g., “I feel frustrated by my child”) and Control comprising four discipline items including two positive (e.g., “I am firm and calm with him or her”) and two negative (e.g., “I tell him or her off or shout at him or her”) items. In addition, scales were generated at each age to depict Negative Feelings (four negative PFQ items), Positive Feelings (three positive PFQ items), Negative Control (two negative discipline items), and Positive Control (two positive discipline items). We then created composite measures for all negative items ( Negativity: four negative PFQ items, two negative discipline items) and for all positive items ( Positivity : three positive PFQ items, two positive discipline items). For each scale, items were summed and averaged by the number of items with positive/negative valence and control/feelings elements as appropriate.

Although face validity for our scales is reasonable and appropriate for the hypothesis-driven nature of the current report, variable internal consistency for these scales was found, with reliabilities lower for scales with fewer items, as is to be expected: 9 year: Feelings α = .68 (Negative feelings α = .75, Positive feelings α = .45), Control α = .44 (Negative control α = .33, Positive control α = .61), Negativity α = .74, and Positivity α = .51; 12 year: Feelings α = .70 (Negative feelings α = .75, Positive feelings α = .50), Control α = .41 (Negative control α = .29, Positive control α = .63), Negativity α = .74, and Positivity α = .52; 14 year: Feelings α = .72 (Negative feelings α = .75, Positive feelings α = .57), Control α = .36 (Negative control α = .25, Positive control α = .63), Negativity α = .75, and Positivity α = .56).

Twin analyses

The classic twin method allows the decomposition of phenotypic variance into additive genetic (A), shared (C), and nonshared (E) environmental components (e.g., Plomin, DeFries, Knopik, & Neiderhiser, 2013 ). Twin intraclass correlations (ICCs) provided an initial approximation of these ACE contributions. Heritability can be estimated as twice the difference between MZ and DZ ICCs, and shared environment as the difference between the MZ correlation and the heritability estimate. Estimates of the nonshared environmental component include measurement error; it is the only source of variance responsible for MZ twin differences and thus is estimated as the extent to which the MZ ICC is less than 1. Structural equation models provide more elegant estimates of these variance components as well as confidence intervals and model fit indices.

As well as fitting the standard univariate twin model (see Figure 1 ) for each of our scales across all ages, because the reliability of some scales was not optimal we further tested our hypotheses using the common pathway model.

In this model (see Figure 2 ), all common genetic and environmental variance is mediated through a single latent factor with age-specific factor loadings that allow influences on change over time ( Martin & Eaves, 1977 ). The common latent factor includes the common variance across the ages and is thus more reliable than the scales at each age. The common pathway model allows each phenotypic variable to be also influenced by specific environmental or genetic factors that are not shared across age, which we refer to as age-specific effects .

Model fitting and all subsequent analyses were done using OpenMx ( Boker et al., 2011 ), which uses minus twice log likelihood (–2LL) as the evaluation of the fit. To verify how well an alternative model fits the data, a relative comparison of the fit statistic (–2LL) is made between the saturated model (the baseline model) and the model of interest (here, the common pathway model). Given that the difference between these statistics follows the chi-square distribution, we used the chi-square test with degrees of freedom equal to the difference between the number of parameters of each model. However, due to the sensitivity of this index to sample size, indices such as the Bayesian information criterion (BIC; Schwarz, 1978 ) or the Akaike information criterion (AIC; Akaike, 1987 ) are commonly used in behavioral genetic research (e.g., Kendler, Gardner, & Lichtenstein, 2008 ), with suggestions that BIC performs better with larger sample sizes and more complex models ( Markon & Krueger, 2004 ). The lower the value of these indices, the better the balance of explanatory power and parsimony indicates better fit.

Genetic Analysis

As a first step in estimating genetic and environmental influence, twin ICCs were calculated separately for the MZ and DZ twins (see Table 2 ). In all cases, MZ twin similarity exceeds DZ twin similarity, indicating some genetic influence. The DZ twin correlations are greater than half the MZ twin correlations, indicating substantial shared environmental influence. Finally, the high MZ correlations indicate a minor role for nonshared environmental factors.

Results from the model-fitting analyses (shown in Table 3 ) were highly similar to those gleaned from the ICCs: genetic influence was significant for all scales, shared environment was substantial, and nonshared environment was negligible especially after discounting error of measurement. The focus of the present analysis was on heritability comparisons between feelings and control on the one hand and negativity and positivity on the other. As a prelude, the standard scales for PFQ Feelings and Control yielded a result to be expected from the literature: At all three ages, parental feelings were significantly more heritable than parental control, as indicated by the nonoverlapping 95% confidence intervals for the Feelings and Control scales. The average heritability across the three ages was 42% for parental feelings and 13% for parental control. As an aside, such comparisons were robust for negative feelings (44%) compared with negative control (27%) and for positive feelings (26%) compared with positive control (6%).

Nonetheless, returning to our study focus, we found across constructs that negative aspects of parenting are significantly more heritable than positive aspects, again at all three ages. For example, for negative and positive feelings, negative feelings showed significantly more heritability than positive feelings, with average heritabilities across the three ages of 44% and 26%, respectively; the pattern was similar for parental control, with average heritabilities across the three ages of 27% and 6% for negative and positive aspects, respectively. Finally, creating scales for all the negativity items and all the positivity items regardless of whether they were on the Feeling or Control scale yielded significantly greater heritability for the negativity than for the positivity, with average heritabilities across the three ages of 44% and 12%, respectively.

Acknowledging the fact that the reliabilities of some scales were less than desirable, we examined our hypothesis further by comparing saturated and common pathway models for each of our eight scales, Feelings, Control, Negative Feelings, Positive Feelings, Negative Control, Positive Control, Negativity, and Positivity across the three ages, thus exploiting the stability of a latent factor for these analyses. The results for this common pathway model (see Figure 2 ) are shown in Table 4 , which includes model fit statistics and parameter estimates. In every case, the common pathway model was found to fit the data at least equally as well as the saturated model, providing a statistical rationale for using the model.

The pattern of heritability differences gleaned from the latent factors in these models remained the same as those for our univariate analyses of each scale at each age, adding further support for our hypothesis. That is, while latent factors for feelings and control differed significantly in their heritability in line with previous research (.38 and .08, respectively), there was additional emphasis on the distinctions between negativity and positivity. Specifically, for both feelings and control, negativity consistently yielded significantly higher heritability estimates than did positivity, a finding that held for the overall negativity and positivity latent factors ( h 2 = .42 and .10, respectively). The pattern of heritability estimates for each of the individual scales calculated from the common pathway model did not differ from those reported in our main univariate analyses. Factor loadings suggested that although age 12 had the strongest influence on the latent factors, all three ages were of similar magnitude. Note that since they were not central to the focus of study (in the interests of space in this brief report), the coefficients of the specific pathway are not reported here but are available from the first author.

Discussion

In the current study, the etiology of positive compared with negative aspects of parental feelings and control was explicitly examined for the first time. A clear pattern of results emerged: the negative side of parenting showed significantly greater genetic influence than the positive side, regardless of whether parental feelings or control were assessed. It is important to note that these results replicated across ages 9, 12, and 14 years, as well as in common pathway models across the 3 years in acknowledgment of the variable reliability of our measures and to add confidence in our findings, with all contrasts between positive and negative aspects of parenting significant in our sample.

Previous reviews have highlighted the lower heritability of parental control compared with parental feelings, suggesting that genetically influenced child traits may be more reflected in parental feelings than in parenting control strategies ( Kendler & Baker, 2007 ; Plomin, 1994 ; Plomin & Bergeman, 1991 ). Further, it has been suggested that parental control encompasses more learned, socially influenced parenting behaviors, whereas parental feelings are more strongly influenced by child characteristics such as temperament and behavior problems (e.g., Kendler & Baker, 2007 ). We too find that feelings show greater heritability than control over all. However, in line with our predictions, we have shown negative control to have greater genetic influence than positive control and negative feelings to have greater genetic influence than positive feelings. We argue that the “dark” side of genetically driven child characteristics plays a bigger role in eliciting parental negativity than do other child characteristics in eliciting positivity across feelings and control. For example, parental negativity encompassing hostility and harsh parenting may be more responsive to genetically driven challenging child temperament than positive features such as warmth and calmness are to less challenging traits. Although positivity versus negativity was not an explicit research question in previous studies, these features lend support to our findings ( Kendler & Baker, 2007 ). Further, a recent study using genetically informed social relations models indicates consistency in negative responses elicited by individuals in the family and the importance of genetics for individual effects for negativity ( Rasbash et al., 2011 ). Distinctions of parenting valence seem to be important for understanding family processes.

One of the earliest studies with relevant data was a study of 850 pairs of high-school twins ( Loehlin & Nichols, 1976 ). In this study, parental control comprised items such as “stricter discipline” that showed little genetic influence, yet there was one important exception—an item involving spanking, which showed considerable genetic influence. Indeed, other studies have similarly shown harsh parenting to reflect genetic influence (e.g., Jaffe et al., 2004 ). This anomaly in heritability estimates could be due to harsh parenting involving more negative affect than other kinds of control (see Plomin & Bergeman, 1991 ). Notably, there is evidence outside the field of parenting of higher heritability for negative compared with positive affect (e.g., Baker et al., 1992 ). The reason that other studies have shown control scales to show less genetic influence than feelings scales may be that the control scales concerned have fewer negative-affective items. In the current study, our Control scale included negative-affective aspects of control.

One caveat is critical here. In categorizing measures of parenting into positive versus negative valence, we do not include maltreatment. That is, the pattern we report includes aspects of harsh discipline, such as yelling and spanking, but not abusive forms of parenting. In one study that explicitly looked at this distinction, Jaffee et al. (2004) found that while harsh discipline was moderately genetically influenced (25%), physical maltreatment was not (7%). These findings suggest that children’s genetic influences are largely irrelevant for their vulnerability to maltreatment and that characteristics of the perpetrator are what are important.

Although not a focus for this brief report, it is pertinent to highlight an additional finding of interest in the current study—that of a considerable shared environmental component both for control overall compared with feelings and for positive compared with negative aspects of parenting. In child-based designs like this one, shared environmental components indicate the extent to which parenting is consistent across children within the family. Our findings suggest that parents report being consistent in their discipline—particularly positive strategies—across members of the twin pair, as well in their feelings of warmth toward their children, once genetic similarities are accounted for.

We acknowledge limitations of the current study, such as the fact that the same parent rated both twins, likely to contribute to the high shared environment estimates in particular. The shared environmental estimates we find here mirror the genetic results in that higher shared environmental influence was found for control than feelings and for positivity than negativity. Although this may reflect genuine similarity in parental treatment strategies and warmth, it is possible that it is a parent reporting bias: parents may be more reluctant to say that they use different control strategies for their children or to admit to having more positive feelings about one twin than another.

We choose to use the simplicity of cross-sectional analyses to illustrate a novel path for parenting researchers within this brief report, with a view to offering a potential steer for more complex research. The robustness of our cross-sectional findings across age supports our perspective, but the findings are, by nature, limited. We acknowledge that the measures we us