The theory of human capital, even if it reckons the importance of time in science, is too short for explaining the existing diversity of scientific output. The paper introduces social capital as a necessary complement to explain the creation of scientific human capital. It connects these two concepts by means of a hierarchical econometric model. Bibliographical databases contain much information which is exploited to figure out collaboration, mobility, publishing habits and institutional characteristics. The two level hierarchical model is estimated on 14 European countries using bibliometric data in the fields of economics.