Defining Genetic Determinism: Three Old Concepts, One New Problem and a Modest Proposal

In this paper, I assess whether certain concepts of genetic causation, namely, the “gene for a trait,” norm of reaction and heritability can capture a feasible version of genetic determinism in the postgenomic era. The result is mostly negative, due to the various shortcomings of those concepts. “Gene for a trait” is obsolete because it implies monogenic causality for human behavioral traits. Norm of reaction, although theoretically the best alternative, is not an option in human subjects, due to ethical considerations. The strength and the weakness of heritability lies in its being obtained by non-experimental methods. The advantage is that it is compatible with polygenic inheritance models and can be estimated by non-experimental methods. The disadvantages are related to its causal interpretation, especially in humans. Besides, the missing heritability problem demonstrated that modern genomic methods like genome-wide association studies come short on accounting for the causal paths from genomes to highly heritable traits. Based on the new understanding of genetic causation, I define a weak form of genetic determinism.