In the pre-history era and the Stone Age human societies lived in groups because of the lack of economic growth and the strong need for each other to obtain food. In this era families were very big. With the growth of agriculture, the notion of family almost evolved into its present form, but evolution of families was not as quick as other west Asian countries. The shortage of water was the main cause of impeded economic growth and urbanism in most parts of Iran before the entrance of Aryans. As a result, families were bigger and related to meet their needs. Entrance of Aryans was accompanied by political evolutions in the region. The powerful Assyrian government was ending, native Iranian folks were tired of fighting this cruel enemy in the western areas, and thus Aryans were enabled to gain power. The Medians were often at war and they progressed in terms of military power. As the Achaemenids gained power, a new era of progress and growth started for west Asian civilizations. The Achaemenids properly learned from civilizations of adjacent tribes and actualized the Iranian culture and civilization with their innate wit and wisdom. The factor that considerably contributed to evolution of the institution of family in Iran in the Achaemenid era, especially with the reign of Darius I, was economic measures taken by Darius. These measures increased the government wealth as well as the body of Iranian society (to a lesser extent). Prevalence of coin on the macro level, creation of new jobs, and growth of wages were accompanied by financial independence of the nation. As a result, people were allowed to form families without the need for large families, and thus families transformed from extended families to nuclear families.
