What is the significance of the finding that some traits are genetically based?

Introduction

Human wellbeing and life satisfaction are influenced by life events, health, economy and social relations1,2. Life satisfaction is also closely connected to personality traits3,4, but the nature of this relation is partly unknown. There is limited knowledge about which specific aspects, or facets, of personality are most important. Further, both personality and life satisfaction are influenced by genetic factors5,6,7,8, but we have inadequate understanding of the role of genetic and environmental factors in explaining the links between personality and life satisfaction. Which traits, and which particular facets, are most important for promoting or obstructing individual life satisfaction? Are the associations accounted for by genetic factors, environmental factors, or both? Does the genetic influence on life satisfaction stem entirely from personality related genetics, or do genetic factors for life satisfaction operate independently of personality?

The scientific study of the good life and wellbeing has prospered in recent years9,10,11. As the field has grown, a number of constructs and approaches have emerged. The construct of subjective wellbeing [SWB] occupies a central position, and is typically seen as comprising three components - frequent positive affect, infrequent negative affect, and presence of life satisfaction12. Life satisfaction represents a global evaluation of life, a mental summarizing of life as good, or not so good, according to the individual’s own values, norms, and ideals13. As such, life satisfaction constitutes the key cognitive component in SWB and positive mental health12,14. In parallel with SWB, the construct of psychological wellbeing [PWB] contains components such as engagement, personal growth, and flow-experiences, thereby focusing more on functioning well than feeling well15,16,17. Research on SWB and PWB represent two different, but complimentary traditions, focusing on distinguishable yet related dimensions of wellbeing overall. The dimensions of SWB and PWB have also been integrated into broader models, such as the tripartite model of mental wellbeing [MWB] including emotional, psychological and also social wellbeing18. Thus, in correspondence with research on taxonomies and the nature of psychopathology [i.e., illbeing], the wellbeing field today addresses several aspects of the good life. Life satisfaction represents a central component in SWB in particular, but features as an important aspect inherent in most models.

Genetics of Wellbeing

Genetic factors appear to play an important role in most human characteristics19 and wellbeing is no exception. Heritability estimates for different conceptualizations of wellbeing typically range from 0.30 to 0.5020,21,22,23,24,25. A meta-analysis of 13 studies from seven different countries and including more than 30,000 twins, reported a weighted average heritability of 0.40 for wellbeing5. This meta-analysis also found substantial heterogeneity in heritability estimates across studies, beyond that expected by random fluctuations, thus verifying the theoretical notion that there is no fixed heritability for wellbeing. Rather, the share of variance accounted for by genetic factors varies across cultures, age groups, and the particular wellbeing phenomena studied. Another meta-analysis by Bartels6, with somewhat different inclusion criteria, samples and analytic strategy reported an average heritability of 0.36 for wellbeing.

There is evidence of a common genetic influence on different wellbeing components such as subjective happiness, life satisfaction, SWB and PWB24,26, but also genetic influences that are specific to the different components26,27. The genetic factors in wellbeing are partly related to the genetic influences on social support28, and inversely, depression29 and internalizing disorders30,31,32. Additionally, longitudinal studies have shown that genetic factors account for most of the stability in wellbeing with heritability for the stable variance, or dispositional wellbeing, estimated in the 70–90% range33,34. By contrast, environmental factors constitute the major source of change in wellbeing34,35.

Despite clear evidence of substantial genetic influences on wellbeing in general, findings on life satisfaction are somewhat divergent, with heritability estimates ranging from zero to 0.5924,32,35,36,37,38. The meta-analysis by Bartels6 examined heritability of life satisfaction specifically, and reported an average heritability of 0.32. Thus, life satisfaction appears to be somewhat more influenced by environmental factors than other dimensions of wellbeing. Further, although levels of life satisfaction commonly vary only moderately with age, there might be age-related moderation of genetic and environmental factors. As life satisfaction represents an evaluation of life-so-far, life at older age likely include more life events, adversaries and accomplishments than life at younger age, thereby suggesting stronger environmental than genetic effects. There is a need for more knowledge about the genetic and environmental influences on life satisfaction in the mature population, measured by validated and reliable multi-item instruments.

Recent advances in molecular genetics have contributed to our understanding of the genetic underpinnings of wellbeing – including heritability. Genome-wide Complex Trait Analysis [GCTA] uses genotyping of common Single Nucleotide Polymorphisms [SNPs] in unrelated individuals to estimate heritability. Rietveld, et al.39 reported that up to 18% of the variance in wellbeing can be explained by cumulative additive effects of genetic variants that are frequent in the population. This suggests that common genetic polymorphisms account for nearly half of the overall heritability of SWB. Genome-Wide Association Studies [GWAS] are used to identify specific genetic variants associated with a phenotype. Recently, Okbay, et al.40 used GWAS in a sample of 298,420 individuals, and identified three credible genetic loci associated with wellbeing. However, these three variants explained only a small fraction [4%] of the variance. Molecular genetic studies expand rapidly and are expected to provide important new insights into the genetics of wellbeing. However, it also seems clear that twin and family studies are unique in their ability to capture the total genetic and environmental factors involved, along with the overall overlap and specificity across different characteristics.

Personality and Life-Satisfaction

Personality refers to relatively stable and characteristic patterns of cognition, emotion, and behavior that vary across individuals. These patterns are commonly described in terms of specific personality traits. The most widely known trait models today are the five-factor and big five models41,42, which converge on five broad personality traits, including extraversion, neuroticism, openness, conscientiousness, and agreeableness. There is a well-established relationship between personality traits and wellbeing in general, and personality and life satisfaction in particular3,4,43. More specifically, the big five traits of neuroticism and extraversion consistently explain substantial amounts of variance in wellbeing. The findings are more mixed regarding the trait of conscientiousness, whereas agreeableness and openness seem to play a limited, or negligible role in wellbeing3,43,44.

The five-factor model of personality is hierarchical with the higher-order domains [traits] comprising a set of lower-order facets45. For example, in the NEO-PI perspective, as developed by Costa and McCrae41, the domain of neuroticism includes the facets of anxiety, hostility, depression, self-consciousness, impulsiveness and vulnerability to stress. Correspondingly, the domain of extraversion includes warmth, gregariousness, assertiveness, activity, excitement-seeking and positive emotions. Despite solid evidence for relations between the general big five factors and wellbeing, there is still limited knowledge about which facets of the traits that contribute the most to wellbeing.

Theoretically, inter-personal facets such as warmth and gregariousness [sociability] contribute to wellbeing indirectly by creating well-functioning social relationships that subsequently influence wellbeing. Social support and good social relations have quite consistently been found to correlate positively with wellbeing28,46,47, and may partly be influenced by personality traits and facets.

There is also theoretical reason to expect factors contributing to accomplishments and goal attainment, in the conscientiousness domain, to be important for life satisfaction48,49,50,51. Life satisfaction judgments consider the gap between actual states and ideal states. Personality facets such as competence, self-discipline, achievement-striving and dutifulness may be important in obtaining ideal states, and are thus likely to predict life satisfaction.

Finally, personality tendencies to certain emotional experiences, such as anxiety or positive emotions may similarly influence wellbeing as life satisfaction judgments are coloured by both current emotional states and by memories of past emotional episodes. For example, a personality disposition to experience positive emotions may contribute to many episodes of joy and enthusiasm. These episodes may constitute a basis for the subsequent evaluation of life so far4,52,53. Thus, from a theoretical perspective both interpersonal facets, accomplishment-related facets and emotional facets would be important in generating a good life.

Empirical examinations of relations between personality facets and life satisfaction are limited. However, a few studies have shed light on the issue. Schimmack and colleagues52 found the depression facet of neuroticism, and the positive emotions facet of extraversion to be the strongest and most consistent predictors of life satisfaction. They concluded that depression is more important than anxiety or anger, and a cheerful temperament is more important than being active or sociable. Quevedo and Abella54 found depression and the achievement striving facet of conscientiousness, but not positive emotions, to be the important facets, whereas Albuquerque, et al.55 identified depression and positive emotions as central, and found an additional effect from the vulnerability facet of neuroticism. Finally, Anglim and Grant56 reported significant semi-partial correlations between life satisfaction and the three facets of depression, self-consciousness and cheerfulness.

These studies have provided important knowledge about the nuanced associations between personality and life satisfaction, and point to some particularly important personality facets. Yet, findings so far are limited, as the results are partly divergent, and mostly based on [young] student samples and convenience samples. Consequently, there is a need for replication of findings and expansion of cultures and age groups studied.

Genetic and Environmental Factors in Personality and Life Satisfaction

Personality traits are relatively stable characteristics, and there is considerable evidence for genetic components57,58. Although associations between personality traits, and partly their facets, and wellbeing are established, there is limited knowledge about the mechanisms involved in these associations. Are the associations between personality and wellbeing due to common genetic factors, and is the entire heritability of wellbeing accounted for by the genetic factors in personality – is wellbeing genetically speaking a personality thing?

A few studies have addressed these questions at the level of broad personality traits. First, Weiss and colleagues59 found a global SWB-measure to be accounted for by unique genetic effects for neuroticism, extraversion and conscientiousness, and by a common genetic factor that influenced all five personality domains. Environmental factors also contributed to the associations, but there were no genetic effects unique to SWB. In a similar vein, Hahn and colleagues38 reported shared genetic effects for life satisfaction and the traits of neuroticism and extraversion, but not conscientiousness. Both additive and non-additive genetic effects contributed to the relation between personality and life satisfaction, and again the entire heritability of life satisfaction was accounted for by personality-related genetic factors. Finally, a study examining personality traits and flourishing found substantial genetic effects on the associations, but also identified a unique genetic influence on wellbeing, unrelated to personality60. This latter study was unique in its focus on the construct of flourishing as comprising both eudaimonic and hedonic aspects of wellbeing, based on Keyes’ tripartite model including emotional, psychological and social wellbeing61, and thereby also involving both feeling good and functioning well.

Thus, a few recent studies have reported exciting evidence of a substantial genetic contribution to the association between personality traits and wellbeing. However, several important questions remain to be addressed. First, no studies to date have examined genetic and environmental contributions to the associations between personality facets and wellbeing. Given the findings for broad personality traits, we hypothesize considerable genetic effects also for their facets. Yet, the magnitude of such effects is unknown. Second, only one study38 has examined life satisfaction specifically – rather than global measures of wellbeing. Third, as previous studies have relied only on short-form measures of broader traits, there is a pressing need for examining both traits and facets in relation to life satisfaction by means of comprehensive, valid, well-established instruments. Fourth, findings from the few previous studies are divergent as to whether the entire genetic effect on wellbeing is due to personality-related genetic influences. Fifth, whereas prior studies have examined samples with broad age ranges, we wanted to examine a specific period in life – middle to late adulthood – to assess how relatively stable personality characteristics contribute to life satisfaction in a life course perspective. Finally, as previous studies have been inconclusive regarding sex-differences in the underlying etiology of wellbeing6,62, we also wanted to test for such differences.

The aims of the current study were to [a] identify personality traits and facets that contribute uniquely to life satisfaction, and thereby pinpoint the dispositional constituents of a happy personality, [b] estimate the heritability of life satisfaction in middle to late adulthood, [c] disentangle the genetic and environmental influences shared by personality traits/facets, and life satisfaction, and finally hence to [d] determine whether all of the genetic influence on life satisfaction is due to personality related genetic factors as suggested by some previous studies.

Results

Correlation and Regression Analyses

As shown in Table 1, neuroticism, extraversion, and conscientiousness were all significantly correlated with life satisfaction, while agreeableness and openness were not. The strongest correlation was found for neuroticism, yet with substantial associations also for extraversion and conscientiousness. In the multiple regression analysis including these three factors, only neuroticism and extraversion showed significant unique contributions. The effects remained when controlling for sex and age. A total of 24% of the variance in life satisfaction was accounted for.

Table 1 Descriptives and associations between big five traits and life satisfaction.

Full size table

We next examined the associations for all the 30 personality facets. Table 2 shows the resulting correlations. A total of 23 facets were significantly associated with life satisfaction. In the neuroticism domain, all facets showed significant correlations, ranging from −0.14 for impulsiveness to −0.51 for depression. Within extraversion, excitement seeking was virtually unrelated [0.05] to life satisfaction, whereas positive emotions [0.30] and activity [0.28] showed substantial associations. In the openness domain, only one facet, ideas, showed a significant but very modest correlation [0.08]. The agreeableness domain was notable for a combination of positive and negative associations. Trust [0.17] and altruism [0.09] were positively associated with life satisfaction, while negative associations were shown for modesty [−0.08] and tendermindedness [−0.08]. Finally, in the conscientiousness domain, all factors showed significant and positive correlations, and in particular competence [0.30] and self-discipline [0.28] appeared to be potentially important.

Table 2 Descriptives and associations between personality facets and life satisfaction.

Full size table

Next, regression analyses were conducted in which all 30 facets were tested simultaneously. Ten facets showed significant and unique effects [Table 2]. In total, these facets explained 33% of the variance [adjusted R2 = 32%] in life satisfaction. Four facets yielded substantial betas, that is above 0.10, and with p