This paper investigates the concept of scientific complexity by analyzing global talent mobility through the lens of a bipartite network connecting countries to scientific fields. We introduce a novel set of metrics based on the Revealed Comparative Advantage (RCA) of countries in specific talent fields, which enables the identification of talent mobility patterns and the classification of scientific fields by their relatedness. Drawing on the Method of Reflections (MR), we derive the Talent Complexity Index (TCI) to measure the sophistication of national talent spaces. We further explore the fitness index to capture the dynamic interplay between country-level capabilities and the complexity of scientific fields. Our findings suggest that the fitness index not only reveals the structural intricacies of scientific ecosystems but also serves as a reliable predictor of a country’s future economic performance. These results underscore the importance of talent mobility and scientific complexity in shaping global economic success.