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Behavioral genetics and cultural evolution have both revolutionized our understanding of human behavior—largely independent of each other. Here we reconcile these two fields under a dual inheritance framework, offering a more nuanced understanding of the interaction between genes and culture. Going beyond typical analyses of gene–environment interactions, we describe the cultural dynamics that shape these interactions by shaping the environment and population structure. A cultural evolutionary approach can explain, for example, how factors such as rates of innovation and diffusion, density of cultural sub-groups, and tolerance for behavioral diversity impact heritability estimates, thus yielding predictions for different social contexts. Moreover, when cumulative culture functionally overlaps with genes, genetic effects become masked, unmasked, or even reversed, and the causal effects of an identified gene become confounded with features of the cultural environment. The manner of confounding is specific to a particular society at a particular time, but a WEIRD (Western, educated, industrialized, rich, democratic) sampling problem obscures this boundedness. Cultural evolutionary dynamics are typically missing from models of gene-to-phenotype causality, hindering generalizability of genetic effects across societies and across time. We lay out a reconciled framework and use it to predict the ways in which heritability should differ between societies, between socioeconomic levels and other groupings within some societies but not others, and over the life course. An integrated cultural evolutionary behavioral genetic approach cuts through the nature–nurture debate and helps resolve controversies in topics such as IQ.

Behavioral genetics and cultural evolution have both revolutionized our understanding of human behavior, but largely independently of each other. Here we reconcile these two fields using a dual inheritance approach, which offers a more nuanced understanding of the interaction between genes and culture, and a resolution to several long-standing puzzles. For example, by neglecting how human environments are extensively shaped by cultural dynamics, behavioral genetic approaches systematically inflate heritability estimates and thereby overestimate the genetic basis of human behavior. A WEIRD (Western, educated, industrialized, rich, democratic) gene problem obscures this inflation. Considering both genetic and cultural evolutionary forces, heritability scores become less a property of a trait and more a moving target that responds to cultural and social changes. Ignoring cultural evolutionary forces leads to an over-simplified model of gene-to-phenotype causality. When cumulative culture functionally overlaps with genes, genetic effects become masked, or even reversed, and the causal effect of an identified gene is confounded with features of the cultural environment, specific to a particular society at a particular time. This framework helps explain why it is easier to discover genes for deficiencies than genes for abilities. With this framework, we predict the ways in which heritability should differ between societies, between socioeconomic levels within some societies but not others, and over the life course. An integrated cultural evolutionary behavioral genetics cuts through the nature–nurture debate and elucidates controversial topics such as general intelligence.

Human neurodevelopment is described in terms of its predictable scaling relationships with primate and general mammalian development. The highly predictable, stepwise nature of early brain development, including neurogenesis, axon extension and synaptogenesis, circuit assembly and initial behavior is contrasted with the more malleable nature of brain development as it interacts with the life history events of birth and weaning, which occur at variable times with respect to neural maturation. The early birth and weaning in humans places them in an unusual developmental niche, decoupled from unique association with the mother, for most of their extended development.

Human neurodevelopment is described in terms of its predictable scaling relationships with primate and general mammalian development. The highly predictable, stepwise nature of early brain development, including neurogenesis, axon extension and synaptogenesis, circuit assembly and initial behavior is contrasted with the more malleable nature of brain development as it interacts with the life history events of birth and weaning, which occur at variable times with respect to neural maturation. The early birth and weaning in humans places them in an unusual developmental niche, decoupled from unique association with the mother, for most of their extended development.