Genes, Circumstances, and Volitional Activities are Not Independent Additive Factors
The conceptualization of the happiness pie and its underlying variance decomposition is only correct when all three factors are independent (i.e., they do not interact and do not covary). As Krueger (2015) has pointed out, this assumption is unlikely to hold. As an example of an interaction, lower well-being due to anxiety might be the result of the interaction of childhood stress with a genetic predisposition (cf. Swann and Seyle 2005).
Considering covariation between the factors influencing happiness, the simple additive model ignores the possibility that the effects of genes on happiness might be largely mediated by circumstantial factors and volitional activities (e.g., Lykken 1999, p. 81). Lyubomirsky et al. (2005) acknowledged that genes influence happiness indirectly through experiences and environments, but they seemed to interpret this only in terms of mitigation of negative genetic influences, as in the claim that “unwanted effects of genes could be minimized by active efforts” (p. 114). It seems equally plausible, however, that positive genetic influences on happiness might be mediated through behaviors that could be classified as volitional activities. For example, Lyubomirsky et al. mentioned exercising regularly and striving for important personal goals as volitional activities, but both the inclination to perform daily physical activity and the tendency to persevere in one’s efforts seem to be partly heritable (Moore-Harrison and Lightfoot 2010; Rimfeld et al. 2016). This is neither particularly surprising (cf. Turkheimer 2000), nor does it constitute support for genetic determinism, but merely demonstrates that the simple breakdown of the three factors into proportions that sum to 100% is unjustified from an empirical point of view.
Furthermore, the distinction between the slices of the happiness pie might reify common misunderstandings regarding the nature of heritability estimates. While it seems popular to assume that high heritability implies low malleability, this is not the case: A trait can be both highly heritable and malleable at the same time. For example, the heritability of general intelligence is high, but education reliably increases intelligence (Plomin and Deary 2015; Ritchie and Tucker-Drob 2018).