After the Neolithic Revolution, pastoralism and agriculture led to more reliable and abundant food supplies, which increased the population and led to specialisation of labour, including new classes of artisans, warriors, and the development of elites. This specialistion was furthered by the process of industrialisation, and Industrial Revolution-era factories. Accordingly, many classical economists as well as some mechanical engineers such as Charles Babbage were proponents of division of labour. Also, having workers perform single or limited tasks eliminated the long training period required to train craftsmen, who were replaced with lesser paid but more productive unskilled workers.