Niko Tinbergen was familiar with both conceptual categories (i.e. the four central questions of biological research and the levels of analysis), the tabulation was made by Gerhard Medicus. Certainly, a humanist perspective always involves a transdisciplinary focus. A good and classic example of mixing very different sciences was the work developed by Leibniz in seventeenth-eighteenth centuries in order to create a universal system of justice.[15]