Broad Spectrum Diets in Arid Australia
Edwards, Douglas A., O'Connell, James F., Antiquity
A characteristic feature of human subsistence as the last glaciation ended was the turn towards new food sources, in a `broad spectrum' transformation. Australia took an unusual course, and the trajectory in its arid zone is especially striking. What were the broad spectrum diets in arid Australia? Why did they arise so late? Did they arise late?
Following the peak of the last glaciation, human diets in most parts of the world changed dramatically. Wild plant and animal foods previously available but not much exploited suddenly became important, sometimes dominant, elements of local diets. Because of the diversity of new foods involved, this change is sometimes called the `broad spectrum revolution' (Flannery 1969). Many connect its onset with other changes in human behaviour, including the appearance of new technologies, larger and more stable settlements, higher regional population densities, increased reliance on food storage, and, in some instances, the development of agriculture and the emergence of complex social organization.
Experts disagree about the causes of this dietary `revolution'. Some see it as a product of terminal Pleistocene climatic changes that made these resources more widely available, and more attractive to potential consumers. Others, noting high processing costs and low nutrient return rates, attribute their adoption to the elimination of previously preferred prey, either by climatic change, human population growth and consequent over-predation, or a combination of the two. Still others take the change in diet to reflect the emergence of social institutions that require more intensive exploitation of all resources, particularly those that are most abundant, regardless of cost and independent of climatic change.
Australia provides an interesting and potentially important example of the problem. Judging from the recent literature, it apparently witnesses the broad spectrum change in diet continent-wide, in combination with the appearance of new technologies, changes in settlement pattern at several scales, and a sharp increase in refuse deposition rates read by many to mark a general increase in population density. But these changes are late: on present evidence no earlier than the mid Holocene, well after the first evidence for similar changes on other continents, and unconnected with any major climatic changes of the kind some see as provoking its onset elsewhere. This difference makes Australia a critical test for any general explanation of this phenomenon, particularly those that appeal to climate as the cause.
Here we discuss the origin of the broad spectrum revolution in Australia, with special reference to the arid zone. We focus on this region because of its size, the availability of an ethnographic record in which the use of broad spectrum resources figures prominently, and because their exploitation may be understandable in terms of the same few constraints region-wide.
We begin with an overview of regional environments and continue with summaries of pertinent ethnographic, paleoenvironmental, and archaeological data. We then elaborate general arguments about the origins of the broad spectrum revolution, and evaluate each in light of the arid Australian data.
The arid zone
The arid zone can be defined as that large part of the continent (c. 5,000,000 sq. km, 70% of its present land surface) where evaporation equals or exceeds precipitation (Figure 1). Analysts have long agreed that its occupation by humans is tightly constrained by the distribution of food and water, both in turn largely determined by climate and local topography.
By definition, the arid zone is hot and dry (Gentilli 1971). Summers are very hot (mean January highs >35[degrees]C); winters are moderate (mean July lows ~5-10[degrees]C. Rainfall is low and highly variable. The annual average is less than 500 mm everywhere, less than 125 mm in the driest parts. …