The main purpose of this paper is to propose the hypothesis that inequality was essential for the sustainability and 'development' of early agriculturally based societies that developed in Prehistory and Ancient History. This was so for varied reasons: there was a need for some members of societies -- the dominant class also called the elite -- to escape from the Malthusian trap. In most cases, agriculture produced a bigger economic surplus eventually. In most cases, agriculture produced a bigger economic surplus eventually. Managerial problems -- such as the ones associated with storage, the division of labor, irrigation, trade -- being part of the consequences of the Neolithic revolution, created pressures to develop more centralized political organizations, a process which led later to the formation of the early states. This result involves an important modification of Malthus' theory. However, inequality -- though necessary -- was not a sufficient condition for the sustainability and economic development of these early societies.