From Survival to Susceptibility: How Relaxed Natural Selection Shapes Global Neurological Disease Patterns

Background: The global burden of dementia and other neurological disorders is increasing rapidly, particularly in low and middle income countries (LMICs). While ageing, economic development, and urbanization are well established contributors, the potential influence of evolutionary processes such as relaxed natural selection, captured through the concept of selection opportunity, has not been fully explored. Methods: This ecological study analysed data from 204 countries to examine the relationship between selection opportunity, measured by the Biological State Index (I _bs ), and the incidence of nine neurological disorder indicators. These included grouped conditions such as total neurological disorders and individual conditions such as Alzheimer’s disease, Parkinson’s disease, and headache disorders. Data were obtained from the Institute for Health Metrics and Evaluation, the World Bank, and the World Health Organization. Statistical analyses included Pearson and Spearman correlations, partial correlations, multivariate linear regressions (enter and stepwise methods), and Fisher’s z-tests to assess global associations and subgroup differences by income level and geographic region. Results: Selection opportunity was significantly and positively associated with global dementia incidence (r = 0.651, p < .001), with stronger relationships observed in Lower-and-Middle-Income Countries settings. After controlling for ageing, national wealth, and urbanization, selection opportunity remained an independent predictor of dementia (β = 0.304, p < .001), Parkinson’s disease (β = 0.290, p < .001), and total neurological disorder burden (β = 0.181, p < .05). In contrast, idiopathic epilepsy showed a strong negative association (β = − 0.623, p < .001), and no significant associations were found for migraine or multiple sclerosis. Conclusions: This study provides new evidence that relaxed natural selection may independently contribute to the global incidence of neurological disorders. Integrating evolutionary perspectives into public health strategies may improve the understanding and management of these conditions, particularly in countries undergoing demographic and health transitions.