Supplementary material to reply to comment by P. A. Washington on “Emergence of Complex Societies after Sea Level Stabilized”
John W. Day Jr., Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge;
Joel D. Gunn, Department of Anthropology, University of North Carolina at Greensboro;
William J. Folan, Centro de Investigaciones Historicas y Sociales, Universidad Autonoma de Campeche, Campeche, Mexico;
Alejandro Yáñez-Arancibia, Unidad de Ecosistemas Costeras, Instituto de Ecologia, Xalapa, Mexico;
Benjamin P. Horton, Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia
Citation:
Day, J. W., J. D. Gunn, W. J. Folan, A. Yáñez-Arancibia, and B. P. Horton (2007), Reply to comment on “Emergence of complex societies after sea level stabilized”
Eos Trans. AGU, 88(42), 429.
[Full Article (pdf)]
We thank Paul Washington [this issue] for his response to our article on urbanization and sea level stabilization. Here, we first respond to specific comments and then add some general comments to explain our original article (Day et al., 2007) in more detail.
Washington refers several times to increased marine productivity. In our article, we linked the initial development of complex social organizations to coastal margin productivity. We defined coastal margin ecosystems to include the continental shelf, nearshore upwelling zones, estuaries (including deltas), and lower river floodplains affected by coastal water levels. Thus, the Nile, Mesopotamia, Indus, Mississippi, and Yellow societies were influenced by coastal margin productivity. The Mississippi valley society was affected by coastal water levels that led to the formation of extensive alluvial floodplains and wetland ecosystems. This effect extended far inland. Today, the bed of the Mississippi is permanently above sea level north of Vicksburg, Mississippi, which is more than 850 river kilometers upstream from the mouth of the river.
We did not imply that the first complex societies did not have an important agricultural grain base. However, the abundant availability of animal protein from marine, estuarine, and freshwater sources provided an important energy subsidy to coastal margin populations, removing the protein and fat restrictions of the more carbohydrate-based Neolithic diet, as well as providing a source of omega-3 fatty acids which are important for neural development and maintenance.
While it is true, as we point out in our article, that grain-based subsistence economies developed in the regions Washington listed, the early Holocene phase of these societies was generally at a suburban scale of less than 2500 persons. Only occasional exceptions occurred at well-known trade nexi. These early Holocene societies, however, typically were not stratified by social classes and did not produce monumental structures requiring the labor of thousands of persons. Calculations by Gibson (1998; 2006) at Watson Brake suggest the population of the builder societies at a few hundred with no indications of social stratification supporting the construction. The later building of mounds at a much larger physical scale at Poverty Point, however, would have required the labor input of thousands of people. Furthermore, the origins of the Poverty Point culture, with its peculiar penchant for stratification and long-distance trade, have been traced to locations in the Mississippi delta. After sea level stabilization, Poverty Point was directly linked to coastal margin ecosystems and productivity.
As Washington points out, following our own cautionary note, sea level rise and the subsidence of coastal zone landscapes pose a significant problem to the verification of the coastal zone origin of complex societies. However, these problems are not insurmountable, as lower Mississippi valley archaeologists have recovered evidence of the coastal zone roots of Poverty Point culture as well as of the far more ancient Paleoindian residents of the area. This pattern of discovery has been repeated in all of the regions Washington lists. In Egypt, predynastic culture followed sea level stabilization even though current evidence does not support the development of the first stratified society in the delta. This is equivalent to what we define as the “Neolithic population inflection”, an archaeologically detectable increase in population, which typically followed sea level stabilization and possessed an advanced ceremonial burial complex reflecting the advent of social classes, but further upstream than in other regions. Because of the high productivity of aggrading lower floodplains and their link to sea level, we included that habitat in our consideration of sea level stabilization. Mesopotamia is a particularly revealing case since there is evidence of longstanding scuffling between Neolithic villages; but here as well, it was only after sea level stabilization that rudimentary monumental architecture appeared in the then-coastal village of Eridu, followed by grand-scale construction at Uruk and other cities further inland.
With regard to the exploitation of riparian grain production, as we pointed out, grain production began in the Near East and other areas of the world soon after the advent of Holocene atmospheric moisture conditions. However, most specifically in Mesopotamia, the occupation of the lower floodplain was absent except for winter grazing of livestock and some opportunistic grain planting until after sea level stabilization. It was only after this stabilization and the establishment of stratified society in the coastal zone that additional intensification of Neolithic domesticated plants was undertaken through irrigation agriculture. We suggest that this intensification process was driven by upper class concerns to expand their hegemony inland and that it required grand scale irrigation projects, necessitating the division of labor and supervision. As Washington points out, this intensification process would have been augmented by the effects of post-sea level stabilization on alluviation in the lower river valleys. Rich river levees and floodplains provided a site for highly productive agriculture. For these reasons, from the beginning we have included lower river valleys of major river systems in what we term coastal margin ecosystems.
Our analysis and that of Washington of the effects of rapid sea level rise in the period between 18,000 and 7,000 years ago is that there would not have been substantial earlier near-shore communities. Rapidly rising sea level would have precluded the development of mature coastal margin ecosystems and attendant high levels of coastal margin productivity, which require 500 years or more to reach maturity. This rapid rise in sea level is attributed to the eustatic (i.e., relatively uniform worldwide change in sea level) contribution, which averaged 10 millimeters per year-1 during deglaciation, but peak rates potentially exceeded 50 millimeters per year-1 during “meltwater pulses” at 19 and 14.5 cal kyr BP (e.g., Alley et al., 2005). The time to maturation of human social organizations must be added to the time for maturation of coastal habitats. Research by Kennett and Kennett (2006) suggests that this would be an additional 500 years. Our figure of an average of 1100 years from sea level stabilization to the onset of stratified society in coastal zone villages supports this combined effect.
In addition, Kennett et al. (2003) carried out a literature review of wetland and lower river valley dynamics in the late Pleistocene and Holocene. During glacial periods and the early post-glacial, rivers flowed across the coastal plain and current continental shelf in deeply incised valleys tens of meters deep and discharged to the ocean over the continental slope. This led to lowered water tables and little interaction between the incised river channel and adjacent uplands. Because of this, there was little coastal and lower alluvial floodplain wetland development. With sea level rise, river channels infilled rapidly and alluvial floodplain development was initiated. The narrowness of the incised valleys and rapid infilling would have precluded significant urban development within the area affected by river channels. Any significant urban development on adjacent uplands would still be evident today.
Thus, the high rate of aggradation and frequent flooding would have limited significant urban development. In addition, when they developed, the earliest Mesopotamian cities (i.e., Eridu, Ur, Lagash, and Laisa) were on the edge of a shallow estuarine embayment caused by sea level rise. By Greco-Roman times, the embayment had filled and the sea was several hundred kilometers further to the south.
We disagree, for reasons stated above, that sea level advance submerged evidence of earlier complex social organizations along continental margins. Empirical (e.g., Fairbanks, 1989; Horton et al., 2005) and modeling studies (e.g., Milne et al., 2005) suggest a significant reduction in eustatic contribution during the Holocene beginning ca. 7,000 years ago. This is not to say that there were not Mesolithic villages along older shores, as was the case in northwestern Europe where excavations on islands off the south coast of Brittany have revealed active exploitation of the ocean. Washington appears to underestimate the ability of archaeologists to revive evidence of ancient settlements and complex societies. For example, in special circumstances along the Black Sea, Neolithic settlements have been detected under the water. These settlements developed because a sill protected the Black Sea from sea level rise for some time into the Holocene (Kerr 1998). More commonly elevated “islands” of sediment appear in deltas caused by occasionally high discharge rates during the climatically unsettled declining stages of the Pleistocene (Hassan 1997).
In addition to our responses to specific issues Washington raised, we need to briefly expand our presentation of circumstances leading to complex social organization from that presented in our article to address Washington's statements. In the broadest terms, our model assumes three background or boundary conditions for the development of civilization, or more specifically, complex social organizations capable of mustering large labor forces to build monumental structures. We define monumental structures as requiring the labor of thousands of people, a labor force too large to be organized, sustained, and guided by non-stratified society. Monumental architecture generally appeared early in the development of complex social organizations to legitimize the power of sun kings or castes (Trigger 2003).
1. The first of the background conditions is that of the Pleistocene. Pleistocene conditions were starkly different from the present. Most pertinent to Washington's concerns is the fact that Pleistocene climate was chronically unstable (Feynman and Ruzmaikin 2007; Thompson, et al. 1997). This was caused by lower global temperatures that were not stabilized by large, warm oceans with extensive coastal shallows such as appeared in the Holocene. As a result, the global climate was susceptible to exogenous forces such as changes in insolation and volcanism. The consequence was a planetary surface that would have been unrecognizable by any modern standard. Continents were dusty, windswept grasslands. There was little atmospheric moisture because of low global temperatures. Shores were steep and craggy because of the precipitous slope of the continental shelf margins where sea level stood.
The human adaptations to the Pleistocene condition were small, nimble societies capable of moving over great distances and having knowledge of resources over vast regions. Broad territories buffered these small, mobile societies from the high probability of sudden changes in their ambient circumstances. Despite unfavorable conditions for the development of coastal zone resources, humans seem to have developed a notable dependence on polyunsaturated fats (omega 3) for gestation and the maintenance of large brained adults. This suggests a certain dependence on coastal zone and lacustrine habitats, as they are the richest and most reliable sources (Broadhurst, et al. 2002).
2. The second background condition pertinent to our understanding of human population aggregates is the melting of the Pleistocene ice sheets from about 18,000 years ago to 7,000 years ago. During this period, precessional insolation maximized during the May-June season, which hurried and lengthened the summer. The global climate encountered an additional source of volatility sourced in glacial meltdown processes. The grandest of these processes were the periodic releases of great quantities of fresh water into the north Atlantic. They halted the worldwide maritime conveyor system and the delivery of warm, moist air to higher northern latitudes, especially around the north Atlantic. The best known of these global temperature downturns was the Younger Dryas between 12,900 and 11,500 years ago. Instabilities appear to have prevented the development of shore species such as coral until after 8,000 years ago (Milne, et al. 2005). However, warmer global temperatures and the development of coastal shallows greatly increased global atmospheric moisture, reversing the Pleistocene conditions of impoverished continental flora.
For humans, this yielded the possibility of transition to modestly larger population aggregates made possible by the increased availability of flora and fauna. These village-scale aggregates of over 500 person required social organizations capable of ordering the lives of people living in permanent settlements. Social organizations were composed of associations or networks of people who assumed differentiated roles. However, populations tended to be small enough that the age-old Pleistocene customs of maintaining egalitarian statuses appears to have continued in the context of these "Neolithic" villages. Settlements were generally focused in foothills and mountains where climate was relatively equitable across the seasons. The classic example is Mesopotamia where settled living developed early in the foothills of the Zagaros Mountains and the coastal mountains of the Levant. The higher temperatures of the lower Euphrates and Tigris floodplains were avoided, except during winter for grazing of newly domesticated animal species.
3. Sea level stabilization followed the reduction in eustatic contribution during the Holocene beginning about 7,000 years ago. As the coastal margins were now along the gently sloping inner continental shelves, broad, shallow coastal margin resources developed. These brackish, warm waters provided exceptionally rich fish and plant food as well as sources of voluminous humid air to moisten nearby coastal plains and more distant mountains through uplift precipitation. The floral and faunal systems of coastal shallows require about 500 years to mature into well-developed sources of food for humans.
Within 500 years of sea level stabilization, Neolithic villages began to appear near continental margin shallows (Kennett and Kennett 2006). Among these villages, the first evidence of stratified society appeared in the form of elaborate grave goods marking the veneration of remains of people of high status. Occasionally, incipient monumental architecture appeared in these near-shore communities. An example is Euridu on the shore of the Persian Gulf. It is clear that in these communities the old social custom of maintained egalitarian status was breaking down. This process was probably driven by the necessity to organize sea-going means of fishing, and to resolve conflicts between coastal groups over access to the exceptional coastal resources. This required the increased status of individuals, or more likely the formation of tribal-scale social groups to special status as organizers and warriors.
For reasons that are not yet entirely clear, complex social organizations inevitably moved the center of their focus from the shore to inland urban centers. The reason probably was that they quickly discovered one of the fundamental rules of military tactics, that one should not locate one's center of political and military control at locations of strategic importance, in this case the fishable shallows.
Our concerns and those of Washington evolve around the transition from step 2 to step 3.
To summarize then, it is our belief that Washington's criticisms are based on two assumptions that we argue are outdated when viewed in the perspective of the sea level stabilization model. First, Washington assumes a gradual increase in the use of grains to support settled life; our model suggests a stepwise change after sea level stabilization. Second, Washington fails to mark the common background condition of sea level stabilization on coastal margin ecosystems that increases the productivity of both delta-estuary resources and lower river valley resources as a common cause of urban civilizations.
The assumption of gradualism in the development of grain-based civilizations is basically the existing model that archaeologists also use. As we develop more fully in our extended online comments, domestication, and perhaps just as important, harvesting of wild grains, seeds, and other plant tissues to sustain villages, developed rather promptly with the onset of the Holocene, generally after 13,000 years ago. This harvesting was especially notable in the Near Eastern Natufian villages, but also elsewhere, for example in New Guinea where people harvested bananas after this time. Domestication apparently came along later, mostly after 10,000 years ago. The apparent lag in domestication is because there are limits to what archaeologists can do in detecting securely domesticated plants. Even so, this worldwide dependence on domesticated and non-domesticated crops continued at a village level until after sea level stabilization. This represents a period of about 6,000 years of relative stable utilization. The few exceptional population centers in this period—such as Jericho and Çatal Hüyük—can be understood as important trade nexi. After sea level stabilization, a qualitative change in the production of then-highly domesticated grains emerged. This is generally explained as extreme intensification though public works, often irrigation projects that exceeded even the labor inputs of monuments and required the labor of thousand of people.
Washington's argument weakens when tries to make a distinction between lower river system sediment accumulation as a result of sea level stabilization and delta-estuary enrichment as a result of sea level stabilization. During the Pleistocene, deeply incised lower river valleys would have been as unproductive as their overlooking uplands. Water tables would have been as deep as the incised channels. Nutrients and clays would have been stripped from old river bed sediments. The reworking of sediments by the meandering and braiding of low-discharge river systems would have conspired to lower productivity. With sea level stabilization, river floodplains rapidly filled with nutrient-rich sediments. Backswamps accumulated clay-rich deposits capable of retaining nutrients. Water tables rose to within a few feet of the surface. Desert civilizations such as Mesopotamia, Indus, and west coast South America turned to these enriched floodplains that to sustain large populations following the establishment of stratified societies in the even much richer coastal zones. In moister environments (Mississippi, Grijalva, Northwest Europe), complex social organizations evolved without, or with little, need for agricultural intensification. As in almost all aspects of its civilization, Egypt is a special case because of the Nile's peculiar volume and floodplain characteristics. Because the characteristics of the Nile took care of most agricultural needs more or less automatically, the population was free to invest in the largest monuments in the world. Nevertheless, here too, the flowering of civilization awaited sea level stabilization, raising an interesting question in itself. As in Mesopotamia, what restrained the development of Egyptian civilization until sea level stabilization?
References
Alley, R. B., Clark, P. U., Huybrechts, P. & Joughin, I.Ice-Sheet and Sea-Level Changes. Science 310, 456-460 (2005).
Broadhurst, C. L., Y. Wang, M. A. Crawford, S. C. Cunnane, J. E. Parkington and W. F. Schmidt
2002 Brain-specific Lipids from Marine, Lacustrine, or Terrestrial Food Resources: Potential Impact on Early African Homo Sapiens. Comp Biochem Physiol B Biochem Mol Biol 131(4):653-673.
Feynman, J. and A. Ruzmaikin
2007 Climate stability and the development of agricultural societies. Climatic Change.
Gibson, J. L.
1998 Elements and Organization of Poverty Point Politcal Economy: High-Water Fish, Exotic Rocks, and Sacred Earth. Research in Economic Anthropology 19:291-340.
2006 Navels of the Earth: Sedentism in Early Mound-building Cultures in the Lower Mississippi Valley. World Archaeology 38(2):311-329.
Hassan, F. A.
1997 The Dynamics of a Riverine Civilization: A Geoarchaeological Perspective on the
Nile Valley, Egypt. World Archaeology 29(1):51-74.
Kennett, D. J. and J. P. Kennett
2006 Early State Formation in Southern Mesopotamia: Sea Levels, Shorelines, and Climate Change. Journal of Island & Coastal Archaeology 1:67-99.
Kennett, J. P., K. G. Cannariato, I. L. Hendy and R. J. Behl
2003 Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis Special Publication Vol. 54. AGU Code: SP0542960.
Kerr, R. A.
1998 Black Sea Deluge May Have Helped Spread Farming. Science 279:1132.
Milne, G. A., A. J. Long and S. E. Bassett
2005 Modelling Holocene relative sea-level observations from the Caribbean and South America. Quaternary Science Reviews 24:1183-1202.
Thompson, L. G., T. Yao, M. E. Davis, K. A. Henderson, E. Mosley-Thompson, P.-N. Lin, J. Beer, H.-A. Synal, J. Cole-Dai and J. F. Bolzan
1997 Tropical Climate Instability: The Last Glacial Cycle from a Qinghai-Tibetan Ice Core. Science 276(5320):1821-1825.
Trigger, B. G.
2003 Understanding Early Civilizations. Cambridge University Press, Cambridge.
