Which human traits did early eugenicists claim were inherited?

Early eugenicists operated under the flawed premise of biological determinism, asserting that a wide range of human characteristics were rigidly inherited and largely unaffected by environmental factors. They sought to categorize various social, psychological, and physical conditions as "defective" traits caused by genetic anomalies.1

The traits and conditions early eugenicists claimed were inherited included:

• Intellectual and Psychological Conditions: Intellectual disability, bipolar disorder, and hyperactivity.1
• Social and Behavioral Conditions: Criminality, alcoholism, pauperism, shiftlessness, and promiscuity. Eugenicists often argued that low mental ability was the root cause of these antisocial behaviors.1
• Physical Traits: Conditions such as cleft palate, clubfoot, dwarfism, and gigantism.1

It is important to note that these claims were often based on biased intelligence tests or subjective observations rather than rigorous scientific evidence. The eugenics movement’s reliance on these pseudoscientific assumptions led to grave ethical violations, including the involuntary sterilization of thousands of individuals deemed "unfit".12