Birth polis-demographic and economic development
Economic development determined by the agrarian revolution during the birth of the polis was a remarkable demographic effect: the ability to keep and take care of the children were higher than before and the number of births increased.
The systematic excavations of places desalinated for burials of Athens' citizens and the rest of the attic territory, in fact, showed that the population of this area, remained stable for centuries, in the 8th century BC grew suddenly and significantly: this is shown with no possibility of doubt by comparison with the number of the tombs of previous centuries.
The increase in the number of burials can be found also in other areas, like Argos and Corinth.
And Sparta, in the same period, was extended towards the South and the Laconia Messinia, driven by a population growth similar to that already highlighted for other cities. The growth of the population, therefore, necessitated the creation of new forms of organization of social life, in most regions of Greece.
Another very clear sign of the growing population, finally, is found also in the movement of colonization, which began around 750 BC: during this period, in fact, cities like Corinth, Megara, Chalcis, Eretria and Miletus sent groups of citizens in distant areas of Sicily, southern France, the Black Sea and of Cyrenaica (North Africa).
Evidently, the lands which these populations had were no longer sufficient to feed the population, or to allow a decent standard of living.