Genetic and Environmental Influences on Girls and Boys Gender-Typed and Gender-Neutral Values

Developmental Psychology 2010 American Psychological Association 2011, Vol. 47, No. 3, 726 731 0012-1649/10/$12.00 DOI: 10.1037/a0021910 Genetic and Environmental Influences on Girls and Boys Gender-Typed and Gender-Neutral Values Ariel Knafo The Hebrew University of Jerusalem Frank M. Spinath Saarland University In this first investigation of genetic and environmental influences on children s values, 271 German twin pairs (50.2% boys) reported their values at ages 7 11 years using the Portrait Values Questionnaire (Schwartz & Rubel, 2005). We distinguished between gender-neutral (conservation vs. openness to change) and gender-typed (self-transcendence vs. self-enhancement) values. Boys differed from girls in the importance given to gender-typed benevolence, achievement, and power values. Gender-neutral values showed moderate (.34) and gender-typed values showed higher (.49) heritability, with nonshared environment and error accounting for the remaining variance. For both sexes, substantial genetic effects accounted for the importance children gave to their respective gender-stereotypical end of the selftranscendence versus self-enhancement dimension. However, dramatic sex differences emerged in the gender-atypical end of the distribution. For girls, low self-transcendence (high gender-atypical values) showed a large (.76) group heritability. For boys, gender-atypical values (high self-transcendence) showed no heritability and a modest (.10) shared environment effect. Keywords: values, gender-typed, development, genetics Supplemental materials: http://dx.doi.org/10.1037/a0021910.supp Values development has been considered a hallmark of socialization (Knafo & Schwartz, 2001; Maccoby, 1992). Accordingly, while a vast body of research exists on values socialization (Schönpflug, 2008), only a handful of studies have been conducted on the relative contributions of genetics and the environment to values (Keller, Bouchard, Arvey, Segal, & Dawes, 1992; Waller, Kojetin, Bouchard, Lykken, & Tellegen, 1990), and none have involved children. We addressed this gap with data from German preadolescents. We distinguished gender-relevant from genderneutral values and investigated the genetic and environmental contributions to these values separately for girls and boys, focusing on gender-typical and gender-atypical values. Values Values trans-situational goals or guiding principles (Schwartz, 1992) are substantially different from personality traits, although the two are related, as values pertain to the desirable qualities while traits describe the person s actual personality (Roccas, Sagiv, Schwartz, & Knafo, 2002). Thus, the strong evidence for the heritability of traits (Plomin, DeFries, McClearn, & McGuffin, 2001), that is, how people are, does not extend immediately to values, that is, what individuals aspire for or see as important, especially because of the important role cultural factors play in values development (Schönpflug, 2008). Studying the relative contribution of genetics and the environment is therefore important for understanding values development. Schwartz (1992) described the values system as being composed of 10 values, representing broad motivational goals (Supplementary Table S1). The values system involves two dimensions: (a) self-enhancement (promotion of self interests; power and achievement values) versus self-transcendence (caring for others; universalism and benevolence) and (b) openness to change (stimulation and self-direction) versus conservation (tradition, security, and conformity) (Supplementary Figure S1). We studied eight of these values. Genetic and Environmental Influences on Values This article was published Online First December 13, 2010. Ariel Knafo, Psychology Department, The Hebrew University of Jerusalem; Frank M. Spinath, Department of Psychology, Saarland University. The authors are indebted to the parents and the twins in the Cognitive Ability, Self-Perceived Motivation, and School Achievement Study (CoSMoS) for making the study possible and to Ella Daniel, Maya Benish-Weisman, and Liat Levontin for their comments on earlier versions of this article. CoSMoS is supported by initial funding from Saarland University. The work of the first author was supported by Israel Science Foundation Grant 31/06. Correspondence concerning this article should be addressed to Ariel Knafo, Psychology Department, The Hebrew University of Jerusalem, Mount Scopus, Jerusalem 91905, Israel. E-mail: msarielk@huji.ac.il The possibility that intergenerational values continuity is at least partially the result of genetic similarity between family members (Knafo & Schwartz, 2008) has been largely ignored by researchers. However, there is evidence for genetic influences on values. In a study of twins reared together and apart, about half of the variance in religion-related values was ascribed to genetics (Waller et al., 1990). In a small study of reared-apart twins, 40% of the variance in work values was associated with genetic factors (Keller et al., 1992). In contrast, Giddens, Schermer, and Vernon (2009) conducted a study of twins in which genetic effects were found for only one of three types of materialistic values studied. In the largest genetic study on values, genetic influences were found for three of Schwartz s 726

GENDER-TYPED AND GENDER-NEUTRAL VALUES 727 (1992) values (Schermer, Feather, Zhu, & Martin, 2008). We therefore hypothesized that genetic and environmental components contribute to individual differences in values priorities. All previous genetic values research has included adults. Although important, such research says little about earlier genetic influences because the relative influence of genetics in many traits tends to increase with age (Knafo & Plomin, 2006; Plomin et al., 2001). We investigated genetic and environmental effects with the twin design, in which monozygotic (MZ) twins, who share all of their genetic sequence, are compared with dizygotic (DZ) twins, who share on average half of their genes. Assuming that both twin types similarly share their environments, higher MZ similarity indicates heritability (the proportion of individual differences in a population under specific conditions attributed to genetic variability). Similarity beyond this genetic effect is attributed to effects of the shared environment (ES; nongenetic influences contributing to similarity between siblings who grow up together), whereas nongenetic twin differences are ascribed to effects of the nonshared environment or to measurement error (NSE; see Plomin et al., 2001, for more details and a discussion of the evidence for and limitations of the twin design). Gender Typing of Values The largest study on sex differences in values included adults from 41 cultures and used two different values measures. In all cultures, women gave higher importance than men to selftranscendence values. In contrast, men gave higher importance to self-enhancement values in most cultures (38 or 40 cultures, respectively, depending of the measures), regardless of the values measure used. Sex differences in other values were less consistent or smaller (Schwartz & Rubel, 2005). Adolescents showed similar results (Knafo & Schwartz, 2004). Sex differences in adolescents occupational values assessed with a different measure have been shown to be compatible with these findings (Weisgram, Bigler, & Liben, 2010). We therefore expected similar findings, with girls giving higher importance to benevolence and boys valuing power and achievement more than girls. The consistent (though small) gender differences in selfenhancement versus self-transcendence values coincide with the gender stereotypes common in many cultural contexts (e.g., Jacobs & Eccles, 1992). Knafo and Schwartz (2008), therefore, defined selfenhancement and self-transcendence values as gender typed. Socialization processes may be different for gender-typed and genderneutral values. First, parents values expectations depend in part on the child s sex (e.g., parents desire higher power values for their sons). Second, in the case of gender-typed (but not gender-neutral) values, children accept the values of the same-sex parent more strongly than those of the opposite-sex parent (Knafo & Schwartz, 2008). Regarding gender-typed variables, the genetic and environmental factors responsible for individual differences across the whole distribution (Iervolino, Hines, Golombok, Rust, & Plomin, 2005) may not be the same ones responsible for the extreme, genderatypical end of the distribution (Knafo, Iervolino, & Plomin, 2005). It is therefore important to study genetic and environmental contributions to gender-typical or gender-atypical values. Thus, we investigated separately boys and girls prioritization of values at the high end of their respective gender-typical (e.g., girls high self-transcendence) and gender-atypical (e.g., girls low selftranscendence) values. Method Participants Participants were 271 same-sex (50.2% boys) MZ and DZ twin pairs who were between 7 and 11 years old (M 9.09, SD 0.81). Local record departments in Northrhine Westphalia and Thuringia, Germany, provided contact details (Spinath & Wolf, 2006). Supplementary Table S2 presents further sample information. Procedure We contacted families by phone or mail to obtain parents and children s approval for sending questionnaires. Questionnaires, including parents informed consent forms, were returned in postpaid return envelopes. Zygosity Zygosity was assessed with parental reports on a measure adapted from Goldsmith (1991). The sample included 77 (28.4%) MZ and 61 (22.5%) DZ male twin pairs and 58 (21.4%) MZ and 75 (27.7%) DZ female twin pairs. Values Measure The Portrait Values Questionnaire (PVQ; Schwartz & Rubel, 2005) was used to assess values. It was designed especially for children and has been used successfully with early adolescents in diverse cultures (Bilsky, Niemann, Schmitz, & Rose, 2005). Item phrasing was slightly modified where we judged the wording as difficult for some children. To reduce overload, we dropped one gender-neutral value (tradition) and one gender-typed value (universalism), leaving 30 items (of the original 40). Each item describes a person s (matched to the respondent s gender) goals, aspirations, or wishes, pointing implicitly to one particular value (e.g., It is important for her to be rich. She wants to have a lot of money and expensive things describes a person for whom power values are important). For each portrait, respondents were asked, How much like you is this person? (indicated on a scale ranging from 1 not like me at all to 6 very much like me). We computed scores for each value by averaging its indicative items ( s.58.82, similar to s in Schwartz & Rubel, 2005), centered on the mean rating given by each child to the 30 items (Schwartz, 1992). Analyses at the item level and at the scale level (Supplementary Table S3 and Figure S2) showed that the children construed their values in accordance with Schwartz s (1992) proposed structure, thus supporting the suitability of the PVQ for preadolescents. The score for self-transcendence versus self-enhancement was computed as the average of the items for benevolence, power (reversescored) and achievement (reverse-scored). The score for conservation versus openness was computed as the average of the items for conformity, security, stimulation (reverse-scored) and selfdirection (reverse-scored). Results Descriptive Statistics and Gender Typing of Values Because twin scores are not independent of each other, we used the scores of one randomly chosen twin per pair for descriptive

728 KNAFO AND SPINATH analyses only. Values importance did not correlate with age, except for security, r.11, p.05. MZ and DZ twins gave similar importance to all the values, and no interaction was found between zygosity and children s gender in the importance of values. Girls scored higher than boys on benevolence, t(268) 6.18, p.001, D.75 (Table 1). Boys scored higher on power, t(268) 2.09, p.05, D.26, and achievement, t(268) 3.16, p.01, D.39. No other sex differences were found, supporting the notion that while conservation versus openness values are gender neutral, self enhancement versus self transcendence values are gender typed. The proportion of male and female high and low scorers is another indicator of gender typicality of values. Although mean differences were moderate, sex differences in the extremes of the gender-typed dimension were substantial. Table 2 presents the distribution of girls and boys who scored low (bottom 20%), high (top 20%), or moderately on the two dimensions. The proportion of girls and boys was about equal for all levels of the genderneutral dimension, 2 (2) 1.49, ns, while the gender-typed dimension showed substantial differences, 2 (2) 8.02, p.05. Most (65%) children scoring on the upper or lower extremes of this values dimension were gender typical (boys scored low and girls scored high on self-transcendence vs. self-enhancement), while 35% were gender atypical, 2 (1) 7.85, p.005. In sum, the self-transcendence versus self-enhancement values dimension was substantially gender typed, which supports our hypothesis. Genetic and Environmental Effects Twin correlations. Different correlation patterns emerged for the two dimensions. In conservation versus openness, both male and female MZ twins correlated moderately positively, while no correlation was found for DZ twins (Table 3). This indicates a moderate genetic effect on this dimension and no ES effect for both sexes. Regarding gender-typed values, different results were found for girls and boys. Again, MZ twins correlated positively. However, for boys, a moderate positive correlation was also found for DZ twins, which was about half the size of the MZ correlation, suggesting an additive genetic effect and no ES effects for boys. For girls, the MZ correlation was high, r.60, p.001, while the DZ correlation was close to zero, suggesting a strong nonadditive Table 1 Means (and Standard Deviations) of the Importance of Values Value Boys Girls Mean SD Mean SD Stimulation 4.43 0.83 4.38 0.85 Self-direction 3.79 1.03 3.77 1.09 Benevolence 4.52 0.65 4.99 0.61 Conformity 3.91 0.75 4.06 0.73 Security 4.01 0.69 4.03 0.72 Power 2.47 1.07 2.20 1.05 Achievement 3.46 0.83 3.14 0.81 Hedonism 4.87 0.63 4.76 0.64 Significant sex difference, p.05. Significant sex difference, p.01. genetic influence on girls self-transcendence versus selfenhancement values. Model-fitting analyses (Mx; Neale, Boker, Xie, & Maes, 1999) divided the variance into genetic and environmental components. Models fit the data well for both values dimensions: conservation versus openness, 2 (8) 1.76, ns, root-mean-square error of approximation (RMSEA).00, Akaike s information criterion (AIC) 14.24; self-transcendence versus self-enhancement, 2 (8) 3.42, ns, RMSEA.02, AIC 12.58. The variance component estimates appear in Table 3. Conservation versus openness. ES effects were estimated at zero for both sexes and could be dropped without affecting model fit. Equating variance components for girls and boys did not reduce model fit, 2 (2) 0.699, ns, and yielded a heritability estimate of.34 with 95% confidence intervals (CIs) [.20,.47]. The NSE accounted for the remaining variance of.66, CIs [.53,.80]. Self-transcendence versus self-enhancement. Heritability was estimated at.43 for boys and as high as.55 for girls. ES effects were estimated at zero for girls and close to zero (.01) for boys and thus were dropped from the analyses, 2 (2) 0.003, ns. Equating variance components for girls and boys did not reduce model fit, 2 (2) 1.75, ns, and yielded a heritability estimate of.49 with CIs [.36,.60]. This estimate, which is outside the range of the CIs drawn for conservation versus openness, is significantly higher. The NSE accounted for the remaining variance (.51, CIs [.40,.64]). Genetic and environmental influences on gender typing of values. Although the genetic and environmental estimates on boys and girls gender-typed values were not significantly different from each other, the different correlation patterns indicated that the nature of the genetic effects on gender-typed values was different for males and females. Moreover, the somewhat higher heritability of girls gender-typed values (Table 3) may indicate that additional genetic factors operate on girls values. To address the different roles of genetics and the environment in boys and girls gender-typed values, we studied the extremities of the distribution of these values. We selected twin pairs that included at least one proband (i.e., an individual with extreme scores on gender-typed values). As described earlier, we chose the upper and lower 20% of the distribution as extreme scores. We defined girls scoring above the 80th percentile and boys scoring below the 20th percentile in self-transcendence versus self-enhancement as gender typical, giving high importance to their gender-stereotypical end of the values dimension. In contrast, boys scoring above the 80th percentile and girls scoring below the 20th percentile on self-transcendence versus self-enhancement values were defined as gender-atypical with regard to their values. Table 4 presents probandwise concordance rates, which indicate the probability that a co-twin of a twin with an extreme score meets the same criterion for extremity (i.e., both are on the high extreme or on the low extreme). For both boys and girls, concordance rates for high scores on gender-stereotypical values were higher for MZ than for DZ twins, suggesting a genetic effect. A different picture emerged for scores on the gender-atypical values. Twin concordances for MZ girls were again higher than those of DZ twins. However, boys twin concordances for genderatypical scores (high self-transcendence) were similar for MZ and DZ twins, indicating ES effects on boys gender-atypical values.

GENDER-TYPED AND GENDER-NEUTRAL VALUES 729 Table 2 Sex Distribution in the Extremes of the Gender-Neutral and Gender-Typed Values Frequency Low (bottom 20%) Moderate (middle 60%) High (top 20%) Value dimension/sex n % n % n % Conservatism vs. openness to change (gender neutral) Male 28 20.7 85 63.0 22 16.3 Female 32 23.5 76 55.9 28 20.6 Self-transcendence vs. self-enhancement (gender typed) Male 35 25.9 80 59.3 20 14.8 Female 19 14.0 84 61.8 33 24.3 We tested the genetic and environmental influences on extreme scores in gender-typed values using DeFries Fulker extremes analysis (DeFries & Fulker, 1985) in Mx (Purcell & Sham, 2003). In this analysis, influences on extreme scores are estimated from mean score differences among probands (extreme), their MZ and DZ co-twins, and the population. A genetic effect (group heritability) is indicated if the mean score of MZ co-twins is higher (closer to that of probands) as compared with that of DZ co-twins. Group ES and NSE effects are estimated for environmental contributions at the extremes. For both girls and boys, substantial group heritability effects were found for scoring high on the gender-stereotypical end of the gender-typed values dimension (Table 4). No ES effects were found. A different picture emerged for the gender-atypical extreme scores. For boys, no genetic effects were indicated on preference for the self-transcendence end of the gender-typed values dimension. Instead, environmental factors accounted for their genderatypical values. The familial resemblance (seen in the similar concordances for MZ and DZ boys) reflects a small influence of the ES, with the remaining high gender atypicality accounted for by the NSE. In contrast, girls gender-atypical values showed substantial group heritability and no ES effects. Discussion Genetic and Environmental Influences The importance given to the two major values dimensions has been shown to be affected in part by heritable factors. Environmental effects of the kind not shared by family members accounted for most of the variance. Genetic effects were similar in magnitude for girls and boys, although heritability of girls gender-typed values was especially high. Finally, the atypical end of children s gender-typed values showed markedly different estimates for girls (strong group heritability) and boys (no group heritability, small ES effect). Our results highlight the importance of both genetic and environmental influences on children s values and the moderating roles of children s sex and gender. Because heritability often increases with age (Plomin et al., 2001), more research is needed with adolescents so that change in Table 3 Twin Correlations and Genetic and Nonshared Environmental Influences on the Importance Given to Gender-Neutral and Gender- Typed Values Variance component estimates Correlations Heritability Nonshared environment and error Value dimension/sex MZ twins DZ twins Proportion 95% CIs Proportion 95% CIs Conservatism vs. openness to change (gender neutral) Male.42.09.40 [.20,.56].60 [.44,.80] Female.33.05.28 [.06,.48].72 [.52,.94] Self-transcendence vs. self-enhancement (gender typed) Male.44.23.44 [.26,.59].56 [.41,.73] Female.60.09.55 [.35,.70].45 [.31,.65] Note. Proportion proportion of variance; CIs confidence intervals. p.05 (1-tailed). p.01.

730 KNAFO AND SPINATH Table 4 Probandwise Concordances, Estimates, and 95% Confidence Intervals of Genetic and Environmental Effects on Extreme Scores in Gender-Atypical and Gender-Stereotypical Values of Self-Transcendence and Self-Enhancement Variance component estimates Type of extremity/zygosity Probandwise concordance Group heritability Group shared environment Group nonshared environment and error Proportion 95% CIs Proportion 95% CIs Proportion 95% CIs Gender stereotypical Low: Male twins.58 [.17, 1.00].00.42 [.00,.82] MZ 0.50 DZ 0.21 High: Female twins.34 [.06,.88].00.66 [.12,.95] MZ 0.46 DZ 0.29 Gender atypical High: Male twins.00.09 [.01,.26].91 [.74,.99] MZ 0.23 DZ 0.21 Low: Female twins.76 [.28, 1.00].00.24 [.00,.72] MZ 0.56 DZ 0.32 Note. Low low self-transcendence vs. self-enhancement; high high self-transcendence vs. self-enhancement; proportion proportion of variance; CIs confidence intervals; MZ monozygotic; DZ dizygotic. the relative importance of genetics and the environment can be examined. For example, while stability is often genetically based, nonshared environmental factors usually account for change (Knafo & Plomin, 2006). Values development is a dynamic process, especially in adolescence when identity is reshaped (Waterman, 1999), and we plan a longitudinal genetically and environmentally informative investigation of values development. The finding of weak ES effects on values may seem at odds with the literature showing correlations between parent child values similarity and parenting (e.g., Knafo & Schwartz, 2001). Tradition values, which were not included in the current investigation, show the highest parent child similarity (Knafo & Schwartz, 2008) and substantial ES effects (Schermer et al., 2008). In addition, some of the effects of parenting may be unique to one of the siblings, as shown in studies of parents differential treatment (Asbury, Dunn, Pike, & Plomin, 2003). It is possible that the effects of meaningful environmental variables, although common to siblings, have a differential impact upon them, dependent on third variables such as specific life events (Plomin, 1994). Finally, culture accounts for a substantial proportion of the variance in values (Schwartz & Rubel, 2005). To the extent that family practices are common to most parents in a given culture with specific values, these effects will not be detected with the twin design. In this scenario, family influences on values will operate at a societal level, rather than at a family level, and will be detected only in cross-cultural studies. Gender Typing of Values Our results showed that the main sex differences in values (Schwartz & Rubel, 2005) already can be found in preadolescence. While the size of mean sex differences was modest, substantial differences were found at the low and high extremes of the distribution of gender-typed values. The notion that selftranscendence versus self-enhancement values are gender typed points out the importance of studying the socialization patterns of these values in a gender-specific context (Knafo & Schwartz, 2008). The findings suggest that separate genetic effects may operate for girls and boys. The finding of additive genetic effects for boys but nonadditive effects for girls replicates the finding of a study on gender-atypical behavior in childhood, an effect which may be related to evolutionary fitness (Alanko et al., 2010). The extremes analyses provided further insight into genetic and environmental contributions to gender-typed values. For both girls and boys, substantial genetic effects accounted for the importance both sexes gave to their respective gender-stereotypical end of the gender-typed values dimension. The remaining variance was accounted for by NSE. However, a dramatic sex difference was found with regards to the gender-atypical end of the distribution. For boys, gender-atypical values (high self-transcendence) showed no heritability at all. For girls, low self-transcendence (high gender-atypical) values showed large group heritability. The environmental components also differed, with girls showing moderate NSE effects, while boys showed only environmental influences on gender-atypical values, including a modest ES effect. The findings of high heritability for gender-atypical values priorities only for girls and a small ES effect only for boys resemble the stronger genetic effects (girls) and stronger ES effects (boys) in young children s gender-atypical behavior (Knafo et al., 2005). As socialization agents emphasize boys gendertyped characteristics more than girls (Maccoby, 1998), these socializing efforts may mask boys genetically influenced tendencies more than they do for such tendencies in girls. Further research is needed to fully address these findings. Limitations Our sample of 542 children, which would be considered large for most purposes, is modest for a twin study. It did not provide the

GENDER-TYPED AND GENDER-NEUTRAL VALUES 731 power necessary for us to compare the heritability estimates of boys and girls or alternative models including additive or nonadditive genetic effects; it also resulted in wide confidence intervals for the genetic and environmental estimates. For length considerations, we did not assess children s tradition and universalism values. In the future, researchers should seek to include these values. Tradition, in particular, may provide important insights into the environmental influences on values priorities. Conclusions The distinction between gender-neutral and gender-typed values proved important, not only to mean sex differences but also to understanding the differential developmental processes involved in boys and girls gender-typed values. Understanding genetic and environmental contributions in the context of gender and the gender relevance of values has profound implications for understanding the development of values. 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Child Development, 81, 778 796. doi:10.1111/j.1467-8624.2010.01433.x Received January 18, 2010 Revision received August 10, 2010 Accepted September 7, 2010