Assessing subclinical psychopathological and personality traits in a small-scale subsistence society.

Background and objectives: Are psychiatric conditions linked to Western, Educated, Industrialized, Rich, and Democratic (WEIRD) lifestyles, akin to other "diseases of civilization", or have they always been part of human variation? Are psychiatric traits always harmful and selected against, or can they be neutral or adaptive in some contexts? Addressing such core questions in evolutionary psychiatry requires examining and quantifying psychiatric symptoms and their subclinical manifestation in radically different cultural and ecological settings, such as small-scale subsistence societies. Available tools designed for the global North are often ill-suited for these communities, failing to translate and to reflect culturally-specific experiences. Here, we present a multi-stage approach for assessing subclinical psychopathological and personality traits among the Tsimane', an Indigenous forager-horticulturalist population in lowland Bolivia. Methodology: Building on established questionnaires, we reviewed over 400 items through extensive collaboration with local research assistants, focus groups, and cognitive interviews. We grounded each item in culturally relevant examples and translated them into Tsimane', ensuring both conceptual accuracy and comprehensibility. Results: The final instrument consists of 117 items associated in Global North settings with autism spectrum disorder, attention deficit hyperactivity disorder, obsessive-compulsive disorder, schizotypy, depression, anxiety, trauma, substance use, and personality. Conclusions and implications: This study provides a model for developing culturally sensitive tools to measure mental health traits in small-scale societies. It contributes to evolutionary psychiatry by laying the groundwork for quantifying subclinical psychopathology and personality traits, enabling rigorous tests of evolutionary hypotheses.