Biological determinism

Biological determinism, also known as genetic determinism, is the belief that human behaviour is principally governed by an individual’s genetic makeup or physiological characteristics, often minimising or excluding the influence of environmental factors. This view assumes that inherent biological traits predetermine personal abilities, moral tendencies, and social behaviours. Although historically influential across multiple scientific and social movements, the concept has been widely criticised and superseded by contemporary understandings of gene–environment interactions, developmental plasticity, and epigenetics.

Definitions and Conceptual Distinctions

Biological determinism holds that genes or physiological features directly cause behavioural outcomes. A related but distinct concept, genetic reductionism, refers to explaining complex phenomena solely in terms of genes, reflecting a methodological stance rather than a causal claim.
Modern behavioural genetics recognises that genes contribute to human variation but operate within the context of environmental influences, learning processes, and developmental pathways. This synthesis undermines rigid determinist models by showing how biological and environmental factors are intertwined.

Historical Context

Biological determinism played a prominent role from the nineteenth to early twentieth centuries through attempts to explain social inequality, intelligence, and moral character in biological terms. These efforts influenced the development of eugenics, scientific racism, and debates about inherited intelligence.

Germ Plasm Theory

In 1892, August Weismann proposed the germ plasm theory, distinguishing germ cells—responsible for transmitting hereditary material—from somatic cells, which form the body. He argued that heredity flowed only from germ cells to somatic cells, not vice versa, thereby rejecting Lamarckian inheritance. This laid the foundation for later genetic theories and contributed to deterministic interpretations of heredity.

Eugenics Movement

Francis Galton, a cousin of Charles Darwin, coined the term eugenics and encouraged selective breeding to reduce the prevalence of what he considered undesirable traits. These included physical conditions such as club foot and psychological traits including alcoholism and criminality. Policies based on this ideology emerged in the United States during the early twentieth century, leading to compulsory sterilisation laws that targeted prisoners, psychiatric patients, and socially marginalised groups. Similar measures appeared in parts of Europe during the 1930s.

Scientific Racism

Biological determinism informed early forms of scientific racism. Researchers such as Samuel George Morton and Paul Broca sought to correlate cranial capacity with skin colour, claiming that larger skulls indicated intellectual superiority. Methodological flaws rendered these findings invalid, but they were used politically to justify slavery, colonialism, and resistance to women’s suffrage. Such work became emblematic of the misuse of biological arguments to support discriminatory ideologies.

Heritability of IQ

Intelligence testing emerged in the late nineteenth and early twentieth centuries. Alfred Binet developed tests intended to measure school performance, not innate ability. However, American psychologists including H. H. Goddard, Lewis Terman, and Robert Yerkes transformed these instruments into tools claimed to measure hereditary intelligence. The tests were culturally biased and often administered under unfair conditions, especially to immigrants, illiterate individuals, and minority groups. Results were used to argue for immigration restrictions and to reinforce racial hierarchies, illustrating how assumptions of determinism distorted scientific interpretation.

Biological Theories of Sexual Orientation

Human sexual orientation spans a continuum from heterosexuality to homosexuality and is influenced by both biological and environmental factors. Research indicates substantial biological contributions, especially among males, through genetic components and prenatal developmental processes. However, determinist interpretations that attribute orientation entirely to genetics have been replaced by more nuanced models highlighting the interplay between multiple influences.

Sociobiology and Evolutionary Debate

The publication of E. O. Wilson’s Sociobiology: The New Synthesis in 1975 reignited debates on biological determinism. Sociobiology sought to explain social behaviour through evolutionary principles, drawing from studies of social insects and other animals. Critics argued that extending these explanations to humans risked reviving deterministic assumptions.
Research into the genetic basis of altruism illustrates this debate. W. D. Hamilton introduced the concept of kin selection, proposing that genes promoting altruistic behaviour could spread if they benefited genetically related individuals. Later studies suggested potential genetic associations with altruistic behaviour, though the evidence remains inconclusive. Some biologists, such as Steve Jones, interpret altruism as partially rooted in genetic mechanisms that promote kin-directed behaviours. In contrast, mathematical models have shown that altruistic strategies may be evolutionarily stable under certain ecological conditions, challenging the idea that selfish traits necessarily prevail.

Nature versus Nurture

In the twentieth century, biological determinism was countered by extreme environmentalism, most notably the tabula rasa view that the human mind begins as a blank slate upon which experience alone writes. By the twenty-first century, both positions came to be considered overly simplistic.
Contemporary science recognises that genes are expressed within specific environments, and gene activity is continuously shaped by internal and external stimuli. Epigenetics has been especially important in demonstrating that gene expression can be modified by developmental conditions, stress, nutrition, and social context.
Twin studies, particularly those involving monozygotic twins, illustrate how individuals with identical genomes can develop distinct behavioural traits due to epigenetic modifications. These findings underscore that heritability does not equate to determinism.

Modern Perspectives on Behaviour

Current scientific understanding emphasises:

• Gene–environment interaction, in which genetic tendencies are influenced, moderated, or triggered by environmental conditions.
• Epigenetic mechanisms, including DNA methylation and histone modification, which regulate gene expression without altering DNA sequences.
• Developmental plasticity, highlighting how experiences shape behavioural outcomes across the lifespan.
• Cultural and social factors, which interact with biological processes to influence human behaviour.