The answers to these questions have been drawn from archaeological evidence, and have painted scholarly ideas of tributary and oikos economies. The general idea of a tributary economy in the 5th and 4th millennia has been deduced from broad archaeological evidence. Individual houses had their own means of production, and there were certain temple buildings within which wealth was concentrated. There was some social stratification, but it was perhaps due to individual talents at hunting or other skills more than social hierarchy.
However, by the late 4th millennium there had been sufficient urbanization and resultant specialization within cities that there were distinct populations: rural primary producers; urban specialists; and the urban elite who administered government, likely couching their authority in the divine.
The failure of this system is hypothetical, but regardless some sort of crisis inflection point must have passed in order for it to fade from the archaeological record and be replaced with the oikos economy.
However, it is unlikely that the oikos economy totally replaced the tributary economy. Rather, there must have still been rural folk who were self-sufficient primary producers; and perhaps members of their family served both in the kin household and one or more non-kin oikoi.
Thus, the oikos economy which emerged was an interconnected web that allowed urban elite to remain posh while relieving lower castes from having to produce sustenance for themselves and also pay an increasingly burdensome tribute.
Tributary economy: 5th and 4th millennia
The elite were urban and depended on the primary producers of the hinterland to grow food and make craft products (who had their own means of doing so), with some of the surplus being collected as tribute. This provided the elite with sustenance, with a portion sometimes set aside in case of disasters, and also funded political control, exotic imports, luxury goods and labor. Tribute demands increased in the 4th millennium, forcing rural folk to either flee to the remote countryside or move to the cities; later, an inability to collect sufficient tribute would precipitate the collapse of the tributary economy as the elite found other avenues of maintaining their lifestyles.
Archaeological evidence at rural settlements reveals that most houses had a range of artifacts for output of food, textiles, pottery and chipped stone tools. Tools were made out of whatever was local and abundant, suggesting that most or all people could access the basic means of production. Sheep, goats, cattle and pigs were grown; and wild ass, gazelle, onager, deer and fish were exploited. Among these, different regions favored certain animals due to the local environment. Wheat and barley were mainly cultivated, as well as lentil and flax. Reeds were woven in mats, and local trees were used for food, fuel and construction; tamarisk, almond, poplar and willow in southwestern Iran, and tamarisk, poplar and date palm in Sumer.
The Ubaid economy was by and large a tributary economy: most households had to produce mundane goods such as food and cloth, with surplus being exacted by elites who may have couched this as a voluntary religious duty. Surplus may have been stored extra to guard against disaster, but records of this indicate that payouts in emergencies were a fraction of the total collected. By the Middle Uruk era in the 4th millennium, it had become the norm for mundane utilitarian goods to be centrally produced in cities. A larger pool of available specialized labor offered elites who could afford to employ it the opportunity to commission luxury goods; also, the laborers needed employment, as the cities were too densely populated and the fields too far away for the laborers to have grown their own food. Simultaneously, and likely as a result of this, tribute exactions were increasing. This may have precipitated sedentary agriculturalists to vote with their feet and become nomads or move to a different region (these outcasts were later targeted by governments and known as habiru), or else move into the city.
House sizes varied, but pottery densities were generally equal, so this was likely due to family size rather than social stratification. Certain houses have unique quantities of certain types of artifacts (ie, mostly just bowls) or bone species (ie, nice gazelles) with occasional correlation house size. Perhaps some persons were just better hunters, but regardless some houses were larger and seem to have had access to better resources. Also, there is heterogeneity in burial goods at a cemetery near Susa. In addition to some disparities at houses, evidence for social stratification arises from the presence of temples. They were generally not much bigger than houses, but were raised on a platform, with niched and buttressed façades, mosaic decoration and recessed portals. They had about the same contents as houses, with the addition sometimes of highly decorated goods and also seals. While it has been suggested that priests led everyday lives outside of temple responsibilities, they likely benefited from the offering of luxury goods (ostensibly for the gods) and the use of authority (indicated by the stamp seals).
Transition: 4th millennium
This decrease in tribute approached (or perhaps reached) crisis levels for some urbanites whose lifestyle depended on rural producers' surpluses. This caused the oikoi -- that is, temples, royal palaces and wealthy estates -- to expand their strictly kin-based households to include a non-kin labor force.
Thus, what followed the demise of the tribute-based economy when tributes diminished, was an oikos-based economy that was an interdependent network that included kin-based households, and oikoi with dependent laborers.
Oikos economy: 3rd millennium onwards
Textual studies have revealed that the Sumerian é and Akkadian bîtum, roughly translated as household, subsumed various entities not included in the modern Western notion of a household. A household meant anything from a nuclear or extended family living under one roof, all the way to grand temples (a deity's earthly residence), royal palaces and public officials' wealthy estates. Temples, palaces and wealthy estates are in modernity referred to as oikoi, with each oikos serving as a socioeconomic unit with a dependent and not-kin-related workforce and management, in addition to animals, pastures, fields, orchards, storage facilities and workshops.
The oikos is identifiable as a large structure (or set of related structures) with evidence of: varied craft residues (bead-making, textiles) and sustenance-related production; storage of raw materials and goods; participation in exchange and accounting; and display and/or exercise of force. With its own accounting and production means, these oikos households must have relied on non-kin labor that was paid in rations, and maintained themselves with some measure of force.
What strongly distinguishes the oikos and tributary economies' archaeological record is that in the oikos economy, non-elites could work in one or more oikoi and receive rations in exchange; thus, many small kin-based households lacked tools and resources for production, with these instead being held by the oikoi.
|Harvesting||Sickle blades (chipped stone or copper).|
|Butchering||Chipped stone blades without sickle gloss.|
|Fishing||Copper hooks, net weights (ceramic or stone), copper pronged tools.|
|Cooking, baking, heating||Ovens, hearths, ceramic cooking pots, ceramic braziers|
|Food Consumption||Charred plant remains, animal bones.|
|Textiles||Spindle whorls (spinning), loom weights (weaving), needles and awls (sewing, leatherworking).|
|Sculpting||Copper chisels, stone hammers.|
|Stone Tool Manufacture||Flint or obsidian cores, bone punches, stone hammers.|
|Personal Adornment||Jewelry: bears, amulets, pendants, rings, pins, etc; toiletry items: cosmetic containers (shell, metal, stone), bone or copper tools for applying cosmetics, copper tweezers.|
|Architectural and furniture adornments||Stone statues, usually in human form, clay or stone plaques, pieces of inlay (shell, stone, bitumen) set into portable objects.|
|Exercise or Display of Force||Stone maceheads, copper dagger blades, axes, spearheads, arrowheads and lanceheads.|
|Receipt of Goods||Clay sealings|
|Preparation of Materials for Exchange||Stone weights|
|Accounts of goods and persons, sales of fields||Tablets|