A theoretical framework that models human behaviour and trait evolution as the product of two interacting inheritance systems—genetic transmission and culturally transmitted information—whereby cultural processes (learning, teaching, imitation) and genetic evolution co-influence selection pressures and trait dynamics across generations.

Principle

Because cultural traits can be transmitted independently and often more rapidly than genes, cultural transmission can modify selection pressures on genetic variants (and vice versa), producing coevolutionary dynamics that neither genetic nor cultural evolution alone would predict.

Demonstration

Hypothetical Demonstration → In a population, a culturally transmitted shift to a new subsistence practice is learnt and copied across families within a few generations; this persistent cultural practice alters resource use and mortality patterns, thereby changing selection pressures on genetic variants related to digestion or disease resistance—analysts model this as interacting inheritance pathways producing coevolutionary change.

Misapplication

Treating cultural transmission as equivalent to genetic inheritance (e.g., assuming cultural traits are encoded in DNA) or assuming genes deterministically fix cultural behaviours; the semantic error conflates distinct transmission mechanisms and ignores modality-specific rates, biases and pathways.

Consequence

Applying the framework clarifies mechanisms for complex human adaptations, guides integration of archaeological, anthropological and genetic data, and frames testable hypotheses about timing and directionality of change; misapplied, it risks biological determinism or reduction of cultural processes to genetic explanations.

Reversal

When cultural transmission is negligible or when cultural traits spread too erratically for sustained selection (e.g., transient fads without intergenerational persistence), genetic evolution proceeds independently and dual-inheritance interactions are minimal; conversely, very rapid cultural change can outpace any detectable genetic response.

Boundary

Clearly within: explanations of persistent traits where both intergenerational cultural transmission and genetic variation plausibly affect fitness across generations. Boundary case: a technology adopted by a single generation and abandoned thereafter—cultural influence exists but is unlikely to shape genetic selection. Clearly outside: one-off learned behaviours that do not transmit beyond individuals or generations.

Semantic Tension

Tension between frameworks that prioritize genetic causation and those that privilege cultural construction; the two must be treated as interacting explanatory layers rather than as mutually exclusive alternatives.

Synthesis

Dual inheritance theory reframes human evolution as multilayered: meaningful explanations emerge only by specifying the transmission modes, timescales and interaction pathways by which cultural and genetic systems shape trait dynamics.