Why Do Psychiatric Disorders Persist in Humans?

Key Points:

• A large-scale genetic study in Nature Communications reveals that psychiatric conditions like schizophrenia, bipolar disorder, autism, and ADHD are linked to specific genetic forms of intelligence—such as creativity, accumulated knowledge, and reaction time—in European populations, offering insight into why these disorders persist evolutionarily.
• The study distinguishes intelligence into three categories: reaction time, fluid reasoning, and crystallized knowledge, each with different developmental trajectories, highlighting that some cognitive traits associated with psychiatric conditions may confer evolutionary advantages.
• Genetic correlations show that while psychiatric disorders often involve cognitive deficits, they also associate with positive traits like creativity and higher educational attainment, suggesting that these genes have been preserved through evolution due to their beneficial effects.
• The concept of pleiotropy explains why it is difficult for evolution to separate advantageous cognitive traits from psychiatric vulnerabilities, as individual genes can influence multiple traits simultaneously, making it impossible to "keep the good and discard the bad."
• The findings caution against simplistic approaches to genetic selection in embryos, as selecting against genes linked to psychiatric conditions might unintentionally reduce desirable traits like creativity, underscoring the complexity of genetic influences on intelligence and mental health.