In recent decades, human capital has become one of the earliest and best-known examples of the application of basic economic concepts to a broader set of topics in human and social behaviour, and Gary Becker was its leading proponent. This expansion of economic analysis has also been associated with a steady development of specialised economic fields that have tried to explore the potential and limitations of using economics to study a large array of topics (Backhouse and Biddle 2000). In the case of human capital, this research has infused several of these applied fields, with particular emphasis on labour economics, the economics of education, growth economics, development economics, population economics, household economics, economic history, and the economics of health.