In their expansive article, Uchiyama et al. address the neglect of cultural evolutionary dynamics in contemporary behavior genetics (BG) models by unification under a dual inheritance (genetics and cultural) model. I concur with their arguments about the need to incorporate cultural evolutionary theory into BG; however, I submit that their proposed model is underdeveloped and their focus on heritability estimates is misguided. I address four issues here: (1) the ambiguity in the conception of culture in the proposed dual inheritance model, (2) the model's neglect of social structure, (3) the lack of a theory of human development and behavior in BG, and (4) the questionable focus on heritability and cross-population comparisons thereof.

Uchiyama et al. correctly, in our view, fault BG approaches for their failure to adequately incorporate cultural evolutionary dynamics. To remedy that deficit, Uchiyama et al. proffer an approach that merges cultural evolutionary theory with BG. Unfortunately, the scope and adequacy of their model is limited by the ambiguity of their key concepts. What Uchiyama et al. mean by “culture” and related concepts – “cultural traits,” “cultural opportunity,” “cultural clusters,” and “cultural inequality” – are not defined. Throughout, Uchiyama et al. seem to conceive of culture as tantamount to social environments or group dynamics, writ large. However, humans are not only cultural; we are hierarchical. The social environments in which we are born and develop include both structural and cultural forces, shaping experiences, constraints, and opportunities.

Although not defined by Uchiyama et al., culture is commonly conceptualized as shared information (beliefs, values, and skills), habits, and styles that exist in human minds and shape collective worldviews or cognitive landscapes (Hannerz, Reference Hannerz1969; Wilson, Reference Wilson2010). Social structure refers to the organized hierarchy of society, including social roles and positions and the social machinery organizing and perpetuating these social positions (Sampson, Reference Sampson2008; Wilson, Reference Wilson2010). Individuals in the same society who share a culture may nonetheless face distinct experiences given their different positions in the social hierarchy – stratified along SES, sex/gender, racial/ethnic, age, and other social positions. A wealth of research highlights the importance of both social structure and culture in shaping behavioral differences, including rich depictions of culture as adaptation to structure (Anderson, Reference Anderson1999; Burt, Reference Burt2018; Massey & Denton, Reference Massey and Denton1993; Patterson & Fosse, Reference Patterson and Fosse2015; Wilson, Reference Wilson2010).

In Uchiyama et al.'s model, different social structural positions and constraints are either ignored or conceived as cultural differences. This both distorts our understanding of culture and impairs our ability to adequately explain human behavioral differences within and across contexts. To fully appreciate and explain the environmental influences on divergent social outcomes of human groups, we must take into account both structure and culture as well as their interplay (Burt, Reference Burt2018; Carter, Reference Carter2003; Patterson & Fosse, Reference Patterson and Fosse2015).

The more significant problem is, however, the deficit of an overarching theory in BG – specifically, a theory of human development and differences. Although Uchiyama et al. suggest that BG explicitly or implicitly adopts evolutionary theory, I disagree. Frequently, BG scholarship seems unconcerned with, even contradictory to, evolutionary theory. The fact that humans did not evolve for educational attainment, wealth, income, happiness, or even longevity – phenotypes commonly studied in BG – but to leave descendants is invariably neglected. Considerations of the goal of evolutionary processes – enhanced survival and fitness in environments that are constantly changing – is often entirely absent from contemporary BG models focusing on phenotypes that capture mainstream WEIRD-cultural notions of “social success” or high status (viz., educational attainment, IQ, risk behavior, and income). (WEIRD = western, educated, industrialized, rich, and democratic.) We are, thus, left with contradictions: BG theorizes “education-related genetics” as reflecting the “winners of the genetic lottery,” even as BG scholarship reveals that present educational attainment and income are associated with lower not higher fertility (Belsky et al., Reference Belsky, Moffitt, Corcoran, Domingue, Harrington, Hogan and Williams2016, Reference Belsky, Domingue, Wedow, Arseneault, Boardman, Caspi and Herd2018). In short, while incorporating cultural evolutionary theory is beneficial, it is not enough. BG has and continues to produce mounds of estimates and evidence, but without a guiding theory it is unable to organize and explain this evidence, including heritability estimates.

Finally, I will note I am perplexed by Uchiyama et al.'s focus on heritability estimates, in general, and their argument for comparing heritability estimates across populations, in particular, as a way of “[cutting] through the nature–nurture debate and [helping] resolve controversies” (abstract). Heritability estimates do not overcome the nature-nurture debate; they perpetuate it. Furthermore, as Uchiyama et al. recognize on occasion, comparing heritability estimates across contexts is foolhardy because heritability estimates are a function of genetic and environmental – cultural, structural, and physical – variation. However, by conceiving of culture as equivalent to the environment, Uchiyama et al. argue that controlling for culture (via proxies of culture such as “cultural looseness/tightness” or the CF_ST) will provide a reference that can shed light on differences in heritability across contexts. Yet, even if we could adequately control for cultural variation – and I think unlikely given that culture is multifaceted and some cultural influences are trait-specific – we would still have uncontrolled structural and physical environmental influences, all of which are constantly changing and interacting. Controlling for culture is not enough because the environment is much more comprehensive. Any results are likely to be partial, at best, and likely misleading. Reconciling BG with cultural evolutionary theory does not make heritability estimates comparable across populations.

In the end, this inability to compare heritability estimates across populations is no great loss. Trying to refine, as we and others have argued, a conceptually and methodologically problematic and ultimately not very useful (outside of controlled breeding) heritability estimate is a wasteful distraction (Burt & Simons, Reference Burt and Simons2014; Turkheimer, Reference Turkheimer2011). As Turkheimer (Reference Turkheimer2011) averred more than a decade ago: “In the real world of humans, in a given context everything is heritable to some extent and environmental to some other extent, but the magnitudes of the proportions are variable from situation to situation, and have nothing whatsoever to do with the causal properties of genes and environments for the trait in question, unless one is interested in the pointless null hypothesis that one of the components is zero” (p. 598). Science is about causal explanations, and heritability is not about either. The time for heritability estimates is past, with or without cultural evolutionary theory.