How did biological determinism support eugenic ideas?

Biological determinism provided the pseudoscientific foundation for eugenics by asserting that human characteristics—including complex social and psychological behaviors—are rigidly fixed by heredity and largely immune to environmental influence.1

By framing social issues such as criminality, pauperism, and intellectual disability as the result of "defective genes," eugenicists argued that society was deteriorating due to the reproduction of "degenerate" populations. This perspective promoted the unethical belief that human worth could be quantified and categorized, often using flawed metrics like early IQ tests to justify the marginalization of disadvantaged individuals.1

Ultimately, biological determinism was used to support the following harmful practices:

• Selective Breeding: Proponents advocated for "positive eugenics" to encourage reproduction among those deemed "well born" and "negative eugenics" to prevent it among those labeled "defective".12
• Compulsory Sterilization: Based on the false premise that social traits were purely genetic, many governments implemented laws to forcibly sterilize individuals in institutions, violating fundamental human rights and bodily autonomy.1

It is essential to recognize that these applications were not only scientifically unsound but also morally reprehensible, as they were used to restrict human potential and justify systemic discrimination.1