Examined Lives: Dual Inheritance Theory (Session 29)

In humans, genes and culture are intertwined streams of inheritance. Consider that our jaws are too weak and our guts are too short for a world without controlled fire and cooked food. In our evolutionary past, we were able to leverage non-genetic adaptations (i.e. culture) to compensate for genetic shortcomings or mismatches. In doing so, we constructed niches for ourselves within which our genes evolved, making us dependent on our cultural inheritance.

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A basic definition of heritability is "the proportion of phenotypic variance for some trait that is explained by genetic variance". Traditionally, biologists calculate heritability of phenotypes by statistically separating genes and environment and seeing how much variance is attributable to genes. In humans, however, the "environment" also includes our inheritable culture which often masks the effect of genes. Without an adequate understanding of humans as a dual-inheritance species, much confusion has arisen in the study of heritability when it comes to IQ, literacy, personality, and other sticky subjects.

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In this session, we will weave our way through some of the puzzles outlined by Michael Muthukrishna to clear up our own thinking on how we humans become the way that we are.

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Recommended background:

‍Cultural evolution of genetic heritability‍
‍(Original peer-reviewed paper. Includes other optional related articles)

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