The hydrologic hypothesis is one which was developed during the early 20th century and is a product of the observation that while agriculture and neo-lithic assemblages developed in various places, that early civilizations flower into history along river valleys. There is also the analogy of the importance of large public works projects to civilization, which the 19th century had begun, and which would accelerate with the 20th century. Finally the hydrologic hypothesis explained the highly centralized nature of capital and wealth in early civilizations, and provided an explanation for the relative stability of these early civilizations. The concept was already quite old by the time Karl August Wittfogel would name the term "hydrologic empire."
Wittfogel's own journey from marxist to anti-communist is comparable to the arc of the idea: in its original incarnation it was a progressive era assertion that the creation of a program of concentration of effort for the public good was fundamental to "civilization." In its middle incarnation it asserted even farther that the nature of civilization was a specialized bureaucracy, and that bureaucracy's functioning was the essential glue of social order. But in the post-war era it became an assertion that ineffective and corrupt empires maintained their control through a "water monopoly" which functioned as a long term rent in support of an inefficient priest-caste, a "agromanagerial despotism."
This hypothesis was attacked, so that by the early 1970's its defenders were on the retreat. For example this is from Mitchell's weak defense in 1973:
Some archaeologists criticize the na- tion that centralized political power in the early states centered around con- trol of irrigation activities. Adams (1960,1969), for example, has argued that in Mesopotamia and Mesoamerica the centralized state developed prior to large-scale irrigation activities. In- deed, he argues (1960:280) that "the introduction of great irrigation net- works [in Mesopotamia] was more a 'consequence' than a 'cause' of the appearance of dynastic state organiza- tion-however much the requiremenu of large-scale irrigation subsequently may have influenced the development of bureaucratic elites charged with ad- ministering them." Other scholars have reached similar conclusions for Mesopotamia (Hole 1966) and Mesoa- merica (Steward 19550, Wolf and Pa- lerm 1955). For Peru, Rowe (1963:20) has found that in lea "large cities appear first and major irrigation canals were only built later. It would be diffi- cult to argue that there was any rela- tionship between irrigation and the development of cities in the area, unless it was that the growth of cities produced a pressure on the land which was met by irrigation projects on an unprecedented scale."
Decontructed, this is about the conflict between appearance of cities, and appearance of irrigation, and goes to the point of the argument that has been being outlined in this piece so far: namely that domestication is the spark and what follows is consequence versus the idea that irrigation takes a scattered neo-lithic system and makes possible civilization and empire.
A large part of the problem with the mid-century version of this hypothesis is that the economic records of several of the areas that supposedly practiced it do not bear out the hypothesis that water management produces a naturally despotic system. The Harrapan civilization of the Indus river valley was not notably despotic, and it does not have the physical marks of being a repressive or centralized state, more to the point, the economic records that we will examine from Summeria will show that the control of the irrigation systems did not lead to the control of the economic system, in fact, the builders were often at the mercy of the temple-market forces.
In the present the hydrologic hypothesis has undergone a revival, but in a very different from. Typical is the work of the Kennetts who recently have combined the "oasis" hypothesis with the assertion that it was river people who would develop irrigation, and that irrigation, not domestication, is the crucial shift in the development of advanced civilizations.
In this context the argument put forward by Douglas Kennett and James Kennett begins with an almost revolutionary manifesto:
The evolution of the earliest complex state-level societies and cities from small sedentary communities took place in southern Mesopotamia between 8000 and 5000 cal yrs BP during the ‘Ubaid and Uruk periods. Attempts to explain this transition often discount the role of environmental change and tend to evaluate available archaeological evidence for urban-based state development either within a static environmental context or assuming conditions similar to those of the present. This practice is no longer tenable given newly available paleoenvironmental records for the region.
This to some extent is a wake up call in the light of already existing evidence, but the mid-1990's the coastline reconstructions of Jenkins were already available, based on coral studies done in the 1980's, and they clearly showed that the Persian Gulf of today, was the Persian Plain of the Dryas and Early Holocene. Reconstructions of pollen and other proxies for condition had also long been available, as had floating tree ring chronologies that clearly showed radical change in conditions. Archeology moves almost as slowly as some of the things that it studies. The touchstone work on the evolution of different river systems, however was "On the geographical position of as yet unexplored early Mesopotamian cultures" in Journal of the American Oriental Society, volume 99, Number 2, April-June, 1979, where Nutzel outlined the series of river systems from the 70Ka to 14Ka glacial system, forward to the present.
The Kennetts point to the growing wave of scholarship in the early part of this decade which began to question the analysis which saw development of states as being entirely "endogenous" – that is internal – and therefore amenable to ergodic explanations.
The gradual filling in of the Persian Gulf is hypothesized to push humans up from the Ur-Schott river value, leaving the evidence of their material culture underwater. In short, an argument for a program of underwater archeology.
While the paleo-climatology is not in question, the gaps in this hypothesis are glaringly large. The first is the admitted on: that geo-political concerns have halted work in this area, one might also add redirected it, as the Saudis are not interested in funding research that would point to Sumerian societies, and the Iranians are most interested in reconstructing the periods of the dominance of Mede, Parthian, and Persian empires much later. The second is that this model would propose the Sumerians as "out of the gulf" along, perhaps, with the Elamites. However, both the Sumerian and Elamite economic systems rest on a herding ethos - the goat part of the Capricorn, which means that they were from the mountains. Their architectural styles also point to a mountain genesis. The "out of the gulf" hypothesis would suppose there being a root ergodive-agglunitive language family rooted in the area under the Gulf. However, there is no cluster of such languages found around the Gulf. Instead, the only possible clusters are far to the north, in the form of the Georgian languages, and far to the East, in the form of the Dravidian languages. There are no Haplotype maps for a genetic movement back from India, hence, it is difficult to draw a coherent movement or diffusion history which works. Nor is the paleo-lithic history from Arabia helpful: instead of seeing the once hypothesized highway from Africa through Arabia over the filled in Red Sea, we find a unique Arabian peninsula industry, which has some backwash into the Horn of Africa.
In short, the linguistic, genetic, and physical evidence point against a founding of the Sumerian culture by in migrating Gulf peoples based on a centralized irrigation political economy. We should expect this. As noted before the hydrologic society always supposed that the need for irrigation and other forms of powerful bureaucracy produced a top down political system to create and control the building of large scale works. Since the Sumerian corpus is very clear on kings as builders, it has a certain straightforward appeal, especially in light of the patterns of centralized of capital seen in the 19th century and early 20th century, whether private or public. The analogy runs this way: "capital needs to be centralized to perform large scale works, thus the presence of such works imply the creation of an information bureaucracy to control them." However, empires come after irrigation, cities come before it. The dry hypothesis may be wrong about "Eden" but it is correct in pointing out that before people had powerful centralization, they had the ability to execute monumental and organized systems.
With the "dry" hypothesis contradicted by missing toolkit and proto-neo-lithic domestications, and the present form of the "wet" hypothesis contradicted by genetic and linguistic evidence, the way is open for a more comprehensive combining of genetic, linguistic, climate, and physical evidence.