Biological determinism

Biological determinism is the position that human behavior, psychology, and social organization are fundamentally shaped — or fully determined — by biological factors: genetics, neuroanatomy, evolutionary history, or physiology. It stands in contrast to cultural relativism and social constructivism, which locate the primary causal forces in cultural transmission, socialization, and institutional structure. The debate between biological and cultural explanations of human behavior is among the oldest and most politically charged in the human sciences, because it intersects directly with questions of individual responsibility, group difference, and the possibilities of social change.

Biological determinism has appeared in several historical forms, ranging from Victorian craniometry and eugenics (which used crude biological proxies to justify racial and class hierarchies) to contemporary behavioral genetics and evolutionary psychology (which make claims of varying sophistication about heritable contributions to behavior). Each version has been attacked on methodological grounds by social scientists and on political grounds by those who argue that biological explanations are systematically deployed to naturalize existing hierarchies. The methodological critiques are often well-founded; the political critiques, however, do not refute the empirical claims and should not be confused with doing so.

The historiography of the debate is a case study in how scientific questions become culturally captured: positions in the biological-versus-cultural dispute correlate more reliably with political commitments than with evidence, which suggests the evidence alone does not determine the outcome.

The Behavioral Genetics Replication Crisis

The empirical program designed to establish the biological basis of behavioral variation has encountered a systematic replication problem that is distinct from — and more damaging than — political critique. It is a failure of the science on its own terms.

Candidate gene studies dominated behavioral genetics from the 1990s through the 2010s. These studies identified associations between specific genetic variants and complex traits — intelligence, depression, aggression, schizophrenia risk, novelty-seeking. The findings were widely publicized and influenced policy discussions about genetic determinism. A 2019 systematic review found that the vast majority of these associations have not replicated in adequately powered independent samples. The serotonin transporter polymorphism (5-HTTLPR) and stress-dependent depression — replicated in hundreds of studies, cited in textbooks — failed to replicate in a 2018 meta-analysis of 450,000 participants (Culverhouse et al., British Journal of Psychiatry, 2018). The candidate gene era is now described by leading researchers in the field as producing primarily false positives, a consequence of small sample sizes, publication bias, and underpowered studies.

Genome-wide association studies (GWAS) and the polygenic score approach that followed represent a methodological improvement: rather than testing candidate variants chosen for biological plausibility, GWAS agnostically scans hundreds of thousands to millions of variants across the genome. The signals it finds are real but modest. Polygenic scores for educational attainment — one of the most-studied behavioral phenotypes — predict approximately 10-15% of variance in well-matched samples. Crucially, the predictive performance of scores trained on European-ancestry samples drops substantially in African-ancestry samples, a finding that complicates any claim that these scores capture universal genetic architecture of intelligence or achievement rather than the genetic correlates of specific socially structured environments.

Twin studies — the methodological foundation of behavioral genetics — have produced a sustained literature challenging the equal-environments assumption (the claim that monozygotic twins experience environments no more similar than dizygotic twins for the traits being studied). Evidence that this assumption is violated for multiple phenotypes does not invalidate twin studies but does complicate heritability estimates, particularly for traits where appearance-based treatment effects are plausible.

These are not political objections. They are methodological findings that constrain what the behavioral genetics literature can support. The distinction the article should draw — and currently does not — is between:

• Weak biological determinism: heritable genetic factors contribute meaningfully to individual variation in some behavioral traits. This is supported by the GWAS literature, though the effect sizes are smaller than earlier candidate gene studies suggested.
• Strong biological determinism: genetic factors primarily determine the socially relevant behavioral differences between individuals and groups. This is not well-supported by the current methodological record, because the methodological program designed to establish it has repeatedly underperformed its promises.

The field is in genuine flux. What it has established is that behavioral variation has some heritable genetic component in studied populations. What it has not established is the magnitude, generalizability, or social interpretability of that component. The gap between those two claims is precisely where the most important scientific and ethical debates live — and where the greatest uncertainty remains.

The empiricist's obligation is to track the evidence, not the agenda. Biological determinism in its strong forms has been a scientific program that has repeatedly promised more than it delivered. The replication crisis in behavioral genetics is not a reason to abandon genetics; it is a reason to read the literature carefully and resist the temptation to report preliminary findings as settled science.