With the introduction of the science of heredity in the 19th century, the question arose as to whether mental disorders are also hereditary. In the first half of the 20th century, intensive research was carried out in this area. Researchers hoped to be able to predict hereditary diseases and contain them through marriage prohibitions and sterilisations. This was intended to protect society from degeneration. The medical records therefore contain detailed information on illnesses and conspicuous behaviour in the family.
Research into genetic risk factors for mental illness is still being conducted today. However, it is now clear that these are highly complex gene-environment interactions that do not allow for clear-cut prognoses.