Dual Inheritance Theory

What is dual inheritance theory?

Dual inheritance theory examines how genes and socially learned culture contribute to change across generations. The key idea is that humans have two routes of inheritance, with different rules.

How it works

Genes pass through reproduction. Cultural information can come from parents, peers, or other people. These routes can interact, but a cultural change need not wait for a genetic change.

Paciotti, Richerson, and Boyd explain how small differences in learning and transmission can accumulate into population-level change. The framework uses models of those processes to connect what individuals learn with what spreads.

Examples and gene–culture coevolution

Language and dietary practices help illustrate the questions. A child can learn words or ways of preparing food from people other than their biological parents. That is cultural transmission. Establishing gene–culture coevolution requires a further step: evidence that a cultural practice changes genetic selection, or that genetic differences affect how culture spreads.

Dairying and lactase persistence

Dairying is a cultural practice: people learn to keep milk-producing animals and use their milk. Lactase persistence is an inherited capacity to continue digesting milk sugar into adulthood. Where adult milk consumption becomes important, variants supporting that capacity can gain a selective advantage. A learned dietary practice can therefore change the conditions under which genetic variants spread.

Tishkoff and colleagues (2007) found lactase-persistence-associated variants in sampled East African populations that differed from the well-known European variant, along with genetic evidence consistent with strong selection. The example involves more than dietary differences: it connects cultural milk use, heritable biological variation and changes across generations. It also shows why gene–culture coevolution should not be told as one identical genetic history for every dairying population.

Why it matters

“Nature and nurture both matter” leaves much unexplained. Dual inheritance theory asks how information travels, how it persists, and how cultural practices and genetic inheritance interact. A particular claim of gene–culture coevolution still needs evidence for that interaction; cultural variation alone is not enough.