ScienceWeek

ARCHEOLOGY: ON THE FAILURE OF HUMAN CIVILIZATIONS

The following points are made by Kathleen D. Morrison (Nature 2006 440:752):

1) Archaeology, it seems, really is a matter of life and death --this was the theme to emerge from a recent meeting [5] convened to address the question of what makes societies more likely to collapse or to achieve long-term sustainability. Just as we do today, our ancestors faced problems of resource depletion, environmental degradation, political instability, demographic pressure and social upheaval. And, as today, success in dealing with these challenges was never assured.

2) Consider the following contrasts. The islands of eastern Polynesia were all settled within a few centuries of one another by people sharing the same ancestral culture. Yet whereas some islands, such as Tahiti, have sustained human populations for centuries, others, such as Easter Island (Rapa Nui), supported populous and complex societies for only a short time before experiencing profound demographic and social disruption. Completely isolated since its initial colonization, variously dated between about AD 750 and 1200 [1,2], this scrap of land came to the notice of the world with the visit of the Dutch explorer Jacob Roggeveen on Easter Sunday, 1722. Roggeveen marvelled not only at the more than 200 massive stone statues, the Moai, which ring the coast, but also at the barrenness of the landscape and the destitution of its small population. The rich soils of Easter Island, oddly enough, supported a depauperate vegetation virtually devoid of woody plants.

3) That Easter Island had once supported a much larger population with a complex political structure was clear from the archaeological record. But it took a combination of archaeological and palaeoenvironmental data (pollen, microscopic charcoal and faunal analysis) to reveal the extent to which the island's degraded landscape was a product of human action. Once covered by subtropical forests dominated by a now-extinct species of large palm [3,4], the island environment was ravaged by intensive human exploitation. With the destruction of plants for canoe-building, offshore food resources such as the marine mammals exploited early in the island's human history receded from reach, as did any chance of mobility as an option for addressing the mismatch between resources and needs. Although ecological constraints certainly played a role in the variable success of human populations on Pacific islands, cultural practices were clearly also crucial. Longer-term sustainability involved agricultural systems and levels of resource extraction compatible with local conditions.

4) Not all anthropogenic environmental change has led to cultural collapse, as both the contrasts between Pacific islands and the evidence from more complex continental contexts shows. One such comparison is between the long-term occupation of the Basin of Mexico and the well-studied collapse of the Classic-period Maya. The Maya, a complex urban society organized into a series of competitive city states, abruptly ceased building monumental structures around the ninth century AD. Large parts of the Maya homeland were depopulated, although others continued to thrive. Many factors -- including environmental degradation, population expansion, warfare and a decline in the ideology of kingship --seem to have been at issue in the collapse. Not far away, however, in central Mexico, the city of Teotihuacan managed to maintain a large population, perhaps as many as 100,000 people, for more than 400 years. The area has continued to support a large population to this day.

References (abridged):

1. Green, R. C. & Weisler, M. I. Asian Perspect. 41, 213-241 (2002)

2. Hunt, T. L. & Lipo, C. P. Science 311, 1603-1606 (2006)

3. Flenley, J. R. & King, S. M. Nature 307, 47-50 (1984)

4. Dransfield, J. et al. Nature 312, 750-752 (1984)

5) Arizona State University, January 31 to February 2, 2006.

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