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People’s desire to be in nature and how they experience it are partially heritable

['Chia-Chen Chang', 'Department Of Biological Sciences', 'National University Of Singapore', 'Daniel T. C. Cox', 'Environment', 'Sustainability Institute', 'University Of Exeter', 'Penryn', 'Cornwall', 'United Kingdom']

Date: 2022-02 

Nature experiences have been linked to mental and physical health. Despite the importance of understanding what determines individual variation in nature experience, the role of genes has been overlooked. Here, using a twin design (TwinsUK, number of individuals = 2,306), we investigate the genetic and environmental contributions to a person’s nature orientation, opportunity (living in less urbanized areas), and different dimensions of nature experience (frequency and duration of public nature space visits and frequency and duration of garden visits). We estimate moderate heritability of nature orientation (46%) and nature experiences (48% for frequency of public nature space visits, 34% for frequency of garden visits, and 38% for duration of garden visits) and show their genetic components partially overlap. We also find that the environmental influences on nature experiences are moderated by the level of urbanization of the home district. Our study demonstrates genetic contributions to individuals’ nature experiences, opening a new dimension for the study of human–nature interactions.

We answer these questions using a twin approach that allows us to tease apart genetic and environmental influences. We use the TwinsUK panel [ 25 ] (number of twin individuals surveyed = 2,306) to examine the extent to which genetic versus environmental influences explain individual variation in nature orientation, the level of urbanization of home location (at the district level), and 4 dimensions of nature experience (frequency and duration of public nature space visits and frequency and duration of domestic garden visits). Based on the assumption of differences in the genetic similarity of monozygotic (MZ) twins (100%) and dizygotic (DZ) twins (50%), we partition phenotypic variance into additive genetic (A), shared environmental (C; shared between the twin pairs), and unique environmental influences (E; unique to each twin individual and including measurement error). After controlling for sex and age, we build a multivariate ACE model with a direct symmetric approach. The multivariate model allows us to examine the genetic and environmental correlations between phenotypes. We also build full bivariate moderation models to further estimate the effect of the level of urbanization of home district on the genetic and environmental influences on nature orientation and of 4 dimensions of nature experience. The full bivariate moderation model allows us to account for potential gene–environment and environment–environment correlations [ 26 , 27 ].

While the importance of combining genetic and environmental factors to understand human behavior is widely recognized [ 24 ], estimating the contribution of genes and environments, or their interactions, to individual variation in nature experience remains unexplored. Here, we estimate the extent to which genetic and environmental influences can explain individual variation in nature experience. Our research questions are the following: (i) are nature orientation, nature opportunity (the level of urbanization of home location), and nature experience heritable?; (ii) if heritable, are there shared genetic bases among these traits?; and (iii) are the genetic influences on nature orientation and nature experience moderated by the level of urbanization of home location?

A person’s nature orientation and opportunity can be shaped by environmental [ 14 , 18 – 20 ] and genetic factors [ 21 – 23 ]. The genetic contribution to nature orientation has been hypothesized, for example, through the biophilia hypothesis [ 21 ], but has never been tested. If such a genetic contribution exists, we can test whether the positive correlation between nature orientation and nature experience could be shaped by a shared genetic basis. By considering the level of urbanization of an individual’s home location (as a proxy of nature opportunity) as a phenotype, we can also test whether there is a genetic component in the level of urbanization of people’s home location and whether it overlaps with the genetic basis of nature orientation (genetic niche picking). If an overlap exists, it may support the mechanism that people would (genetically) choose to live in rural/urban areas through their strong/weak nature orientation. However, as other socioeconomic factors may constrain individuals in their choice of home location, the level of urbanization also functions as an environmental factor influencing a person’s nature orientation and nature experience. Such an environmental factor (the level of urbanization) may also moderate the genetic effects on nature orientation and nature experience (i.e., through gene–environment interactions).

The causes of variation in people’s experiences of nature include their opportunities to interact with nature and their orientation toward obtaining such experiences [ 8 , 11 , 12 ]. On the one hand, people living in places with more nature available (nature opportunity) tend to interact with nature more frequently [ 5 , 11 , 13 – 15 ]. On the other hand, people with a stronger desire to experience nature (nature orientation), with a higher willingness to travel farther to experience nature and to spend more time in gardens, are likely to gain more experiences of nature [ 5 , 11 , 14 , 16 , 17 ]. Nature orientation and opportunity are, however, not independent from each other [ 12 ]. For instance, individuals who have a strong nature orientation may choose not to live in highly urbanized areas [ 13 ]. Alternatively, nature opportunity may enhance a person’s nature orientation [ 12 ]. These cause–effect relationships with many possible causal connections are extremely hard for correlative studies to disentangle.

In recent decades, human populations have shifted markedly from rural to urban environments, with more than 55% of people now living in cities [ 1 ]. While there are advantages to urbanization, urban living is, nonetheless, associated with poorer mental health, reduced subjective well-being, and a higher risk of psychiatric disorders [ 2 – 4 ]. A reduction in nature experiences in urban environments has been shown to be a key risk factor for mental health issues and is associated with an increased risk of anxiety and depression [ 5 – 7 ]. However, there is marked variation in the extent to which individuals within populations have nature experiences [ 8 – 10 ], and this inevitably affects who receives the associated physical and psychological benefits from experiencing nature [ 6 ].

Unstandardized genetic and environmental variances (upper panels) and heritability (lower panels) in (A) nature orientation, (B) frequency of public nature space visits, (C) duration of public nature space visits, (D) frequency of garden visits, and (E) duration of garden visits as a function of level of urbanization of the home district (urban; 0 = rural areas, 1 = highly urbanized areas) based on the moderation models controlling for age and sex. The thick lines are the estimated variances at different levels of urbanization, and the thin lines are the 95% CIs. Model comparisons to test the statistical significance of the moderation effect are shown in S3 Table . CI, confidence interval. The data and code underlying this figure can be found at https://doi.org/10.6084/m9.figshare.17054540.v1 .

Our moderation models tested whether the level of urbanization of the home district moderated the genetic and environmental influences on nature orientation ( Fig 4A ) and nature experiences ( Fig 4B–4E ). The path coefficients are shown in S2 Table , and model comparisons to test the significance of moderation effects are shown in S3 Table . The unique environmental influence on the frequency of public nature space visits was significantly reduced with increasing levels of urbanization ( Fig 4B , S3 Table ), but unique environmental influence on the frequency of garden visits was significantly increased with increasing levels of urbanization ( Fig 4D , S3 Table ). However, we did not detect any significant change in the genetic influences on nature orientation and nature experiences across the levels of urbanization ( Fig 4 , S3 Table ).

There were negligible shared environmental influences on nature orientation and 4 dimensions of nature experience ( Fig 2 ), but a moderate shared environmental influence on the level of urbanization of the home district (39%, 95% CI = 22% to 55%, Fig 2 ). The unique environmental influences explained more than 50% of the individual variation in all 6 phenotypes ( Fig 2 ). However, there were generally low unique environmental correlations among these phenotypes ( Fig 3B , e.g., unique environmental correlations between nature orientation and frequency of public nature space visits = 0.23, 95% CI = 0.16 to 0.29). These results indicate that there may be different environmental factors influencing a person’s nature orientation, nature experiences, and whether a person lives in a rural/urban area.

Estimates of (A) genetic and (B) unique environmental correlations of nature orientation (orientation), level of urbanization of home district (urban), frequency of public nature space visits (nature freq), duration of public nature space visits (nature duration), frequency of garden visits (garden freq), and duration of garden visits (garden duration) from the multivariate model controlling for sex and age using a direct symmetric approach. Error bars = 95% CIs. The genetic correlations were not estimated if there was negligible heritability ( Fig 2 , the CI of heritability includes negative values). CI, confidence interval. The data and code underlying this figure can be found at https://doi.org/10.6084/m9.figshare.17054540.v1 .

There was a high positive genetic correlation between nature orientation and frequency of public nature space visits (0.59, 95% CI = 0.30 to 0.88, Fig 3A ) and a moderate positive genetic correlation between nature orientation and frequency of garden visits (0.43, 95% CI = 0.04 to 0.80, Fig 3A ). These results indicate that genetic components of individual variation in nature orientation and frequency of nature experiences are partially shared; a higher level of nature orientation may predispose individuals to visit parks and gardens more frequently or vice versa.

Standardized genetic and environmental variance explained in nature orientation, level of urbanization of home district (urbanization level), frequency of public nature space visits (nature frequency), duration of public nature space visits (nature duration), frequency of garden visits (garden frequency), and duration of garden visits (garden duration) with the multivariate model controlling for sex and age using a direct symmetric approach. Error bars = 95% CIs. CI, confidence interval. The data and code underlying this figure can be found at https://doi.org/10.6084/m9.figshare.17054540.v1 .

In our multivariate ACE model, nature orientation (heritability = 46%, 95% confidence interval (CI) = 26% to 67%), frequency of public nature space visits (heritability = 48%, 95% CI = 27% to 70%), frequency of garden visits (heritability = 34%, 95% CI = 13% to 57%), and duration of garden visits (heritability = 38%, 95% CI = 16% to 62%) were moderately heritable ( Fig 2 ). There was negligible heritability for the level of urbanization of home district and duration of public nature space visits ( Fig 2 ).

No overlap between MZ and DZ correlations implies genetic influences on the traits. The intraclass correlation with traits controlling for sex and age is included in S1 Table . CI, confidence interval; DZ, dizygotic; MZ, monozygotic. The data and code underlying this figure can be found at https://doi.org/10.6084/m9.figshare.17054540.v1 .

MZ twins were more similar to each other in nature orientation and 3 of 4 dimensions of nature experience (frequency of public nature space visits and frequency and duration of garden visits) than DZ twin pairs ( Fig 1 ). By contrast, the intraclass correlation between MZ pairs and that between DZ pairs on level of urbanization of their home district and on duration of public nature space visits partially overlapped ( Fig 1 ), suggesting weak genetic influences.

Discussion

The results demonstrate genetic contributions to nature orientation and nature experience, while environmental contributions are the predominant source of individual variation. We also find that the genetic basis of nature orientation and of frequency of nature experience partially overlap, as supported by positive genetic correlations. The environmental factors for nature orientation and those for nature experience may be different, with low environmental correlations, suggesting that diverse behavioral interventions or urban planning strategies might be necessary to increase the well-being benefits that people can gain from nature experiences. The environmental influences on frequency of nature experience were further moderated by the level of urbanization of the home district.

Importance of genetic and environmental contributions Our results shed light on the debate on the cause–effect relationship between nature orientation and nature experiences [11–13] by suggesting that their relationship is due to a partially shared genetic basis. One potential mechanistic explanation is that some genes underlying nature orientation (i.e., a stronger desire to seek nature experience) might drive a person to experience nature more frequently. Importantly, the role of nature orientation goes beyond simply visiting nature, and it may also mediate the amount of psychological well-being that a person gains from nature experiences. There is evidence that people who are more oriented toward nature can reap more psychological benefits from nature experiences, such as improved life satisfaction or mood [28–30]. However, unlike life satisfaction and mood, a high level of nature orientation may not be necessary for one to gain cognitive benefits from nature experiences [31,32]. Considering the genetic component of nature orientation, individuals with certain genetic variants may be more responsive to exposure to natural environments when it comes to their psychological well-being [33]. Despite the genetic influences, environmental factors explained more than half of individual variation in nature experiences. The environmental factors influencing nature experience may include, among others, the travel time and distance to the nearest nature space and the quantity and quality of nature that is accessible to the individual [14,15]. But these environmental factors for nature experience do not necessarily associate with those influencing nature orientation, as noted by their low but positive environmental correlations. The lack of a substantial overlap in environmental factors influencing nature experience and nature orientation highlights the importance of diverse urban planning in providing accessible and good quality natural spaces, along with separate interventions to strengthen an individual’s orientation toward experiencing nature. We find very little genetic influence on the level of urbanization of home district, while about 40% of individual variation can be explained by the shared environmental factors. The shared environmental factors may respond to, for example, socioeconomic factors. For instance, socioeconomic status may correlate with access to nature [19,34–36]. Despite the commonly reported relationship between level of urbanization and nature experience [5,11,13–15], the unique environmental correlations between them were low. This may be because the level of urbanization was quantified at the district level due to confidentiality reasons, and people in the same district could differ markedly in their actual opportunity to visit nature spaces. The unique environmental correlation between the level of urbanization and public nature space visits may be higher if future studies have access to higher resolution spatial data.

Influence of age on genetic and environmental contributions A person’s nature orientation has been suggested to result from learning (i.e., through environmental factors) based on the observation that children prefer urban over natural environments, and such urban preference declines with age [32]. While Meidenbauer and colleagues documented the change of mean preference for natural environments across age, we focused on how individuals differ from each other by comparing the similarity between MZ twins and the similarity between DZ twins to estimate the sources of individual variation [32]. Our results are not necessarily at odds but complement findings in [32], since a learned behavior does not conflict with evidence of a behavior being heritable (e.g., academic performance is highly heritable in adequate environments [37]). Similarly, nature orientation could be partially heritable but requires the right environment for its expression. Our study reveals a low shared environmental influence (such as parental family) on nature orientation. It is possible that this parental effect on nature orientation, as reported by [32], is only strong for children and teenagers, and we were unable to detect such effect as our study population comprised relatively old adults (mean = 60.4, ranging from 19 to 89). This seemingly opposing result could be explained by parental influence not lasting and declining once individuals leave the parental home [38]. Future studies performing twin analyses on nature orientation using children or teenagers could help complement our study, and we hypothesize that the shared environmental influences might be higher than those we observed in relatively old adults. Heritability may not be constant across ages [39,40]. Our age moderation analyses (S1 Note) show that the heritability of frequency of public nature space visits reduced with age, driven by increased unique environmental influences. The increased unique environmental influence across age could be due to multiple mechanisms. First, there are more environmental factors that affect elderly individuals in deciding the frequency of their nature space visits, such as accessibility to a green space with specific facilities. Second, the same environmental factors may affect young and old individuals, but these environmental factors have stronger influences on older individuals. Third, the environmental influences may change from generation to generation (i.e., people born in different periods have different experiences), but not with age (i.e., development of individuals). Future research could consider long-term repeated measurements of twin individuals to ascertain the mechanisms underlying changes in the genetic/environmental influences on nature experiences.

Moderation of the level of urbanization on environmental contributions The results show reduced unique environmental influences on frequency of public nature space visits in highly urbanized areas. This could be due to limited public nature spaces in highly urbanized areas [9], which may limit the opportunities of nature space visits for most urban residents. This suggests that a person’s (genetically predisposed) nature orientation could be more important in explaining individual differences in frequency of nature space visits for urban residents as they may be more inclined to overcome these barriers to visit nature space in urban settings or to travel to rural areas. The unique environmental influence on frequency of garden visits increased with the increasing level of urbanization. The uneven access to a garden for urban residents (S1 Fig) might explain the increased environmental influences of garden visits in the highly urbanized areas. Post hoc analyses using only twin individuals in which both twins reported owning a garden (999 twin pairs, 87% of 1,153 twin pairs) showed that the increased unique environmental influence on the frequency of garden visits was no longer evident (S2 Fig, S4 and S5 Tables), suggesting that having access to gardens may be a key factor to explain individual variation in garden visits for urban residents. In the post hoc analyses using only twin individuals in which both twins reported owning a garden, we also observed that the increased genetic influences on the frequency of garden visits for all twins changed to have a decreasing trend (despite not a statistically significant result, S2 Fig). This reversal may suggest that the changes of genetic influences for garden visits across levels of urbanization ought to be interpreted with caution, as reflected in the large CIs of genetic influences at the high levels of urbanization. In the studied population, fewer participants live in highly urbanized environments, and, among those, few own a garden. This may then have limited the power of the moderation analysis on the genetic influences, and future studies could usefully include more urban residents.

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