Genetic determinism

Genetic determinism is the position that an organism's traits — including behavior, cognition, and personality — are primarily or fully determined by its genetic makeup, with minimal or no significant contribution from environmental factors, development, or experience. It is the strongest form of biological determinism and, in its strict form, is not held by any serious contemporary scientist. What is contested is the degree to which genetic factors constrain or predict behavioral outcomes in real populations — a question the behavioral genetics research program has approached with results that are real but modest.

Genetic determinism should be distinguished from the empirically defensible claim that genetic variation contributes to phenotypic variation: heritability estimates for many traits are substantial (0.3-0.8 in well-studied populations), meaning that a meaningful fraction of phenotypic variation in those populations is statistically explained by genetic differences. This does not mean genes determine traits in any strong sense: the same genotype produces different phenotypes in different environments (phenotypic plasticity), gene expression is regulated by epigenetic mechanisms, and the interaction between genetic and environmental factors is often non-additive in ways that make "genes versus environment" a false dichotomy. What heritability estimates measure is the proportion of variance explained by genetic differences in a particular population in a particular environment — not the proportion of the trait that is "genetic" in any more fundamental sense.

The persistence of strong genetic determinist views in popular discourse, long after the scientific community has abandoned them, reflects the political utility of determinism: if behavioral outcomes are genetically fixed, they are beyond the reach of social intervention, and existing inequalities are naturalized as biological fate. This is the political use of a scientific claim that the science does not support.