A theoretical model that describes how genetic and cultural traits evolve jointly through distinct but interacting transmission processes—genetic inheritance and socially mediated cultural transmission—such that cultural practices can change selective environments for genes and genetic predispositions can bias patterns of cultural learning; applied at population and multi‑generational scales to explain trait dynamics that neither genetic nor cultural evolution alone predicts.

Principle

When cultural traits alter individual fitness or the environment, they modify genetic selection pressures; conversely, genetically based cognitive or physiological biases shape which cultural variants are preferentially transmitted, producing coevolutionary dynamics unique to coupled inheritance systems.

Demonstration

Illustrative scenario: In a hypothetical pastoral population a culturally transmitted practice of milk fermentation reduces gastrointestinal disease. Recognition: public health improves for cultural practitioners. Action: individuals with genetic variants conferring lactase persistence experience higher relative fitness. Consequence: over generations the lactase‑persistence allele increases in frequency through selection driven by a culturally created niche.

Misapplication

Treating the theory as implying genetic determinism (that culture is reducible to genes) or as claiming culture is merely an epiphenomenon of genetics. The error is conflating interaction with identity: dual inheritance posits reciprocal influence, not reductive equivalence.

Consequence

Explaining trait distributions requires modeling both transmission modes and their feedbacks; predicts possible rapid cultural change without immediate genetic response, persistent maladaptive genetic variants under strong cultural buffering, and gene–culture correlations emerging causally from cultural practices.

Reversal

When cultural transmission is negligible or entirely individual‑level and non‑heritable across generations, or when selective differentials are too weak, genetic and cultural dynamics effectively decouple and single‑system evolutionary models may suffice.

Boundary

Clearly within: explanations of dietary, technological, or social practices that affect fitness and show correlated genetic change. Boundary case: behavioral tendencies with both biological predispositions and recent cultural shaping requiring empirical analysis. Clearly outside: accounts that treat culture purely as individual learning without cross‑generational transmission or models that ignore genetic feedback entirely.

Semantic Tension

Tension between proximate psychological mechanisms (individual learning biases) and ultimate evolutionary explanations (population‑level selection): both are necessary but operate at different explanatory levels.

Synthesis

Jointly modelling genetic and cultural inheritance reveals that novelty can arise from cultural modification of environments, so understanding human evolution requires coupling social transmission processes with selection rather than treating genes or culture as sole drivers.