Wednesday, November 23, 2011

Analyzing Dietary Remains of the Past

With the theme of Thanksgiving in mind our thoughts this week turn to diets. Nothing to do with dieting, rather we’d like to look at what people have eaten for the past few thousands of years. Most people immediately think about deer, elk or bear for meat, some may think of corn or grains. The diet of native peoples was very diverse and complex and changed over time in conjunction with changes in the environment. You might wonder how archaeologists are able to recreate a picture of the foods consumed by native peoples thousands of years ago.

Paleoethnobotany is the science which looks at the relationship between humans and plants. How humans impact the development of plants and the level of labor required to process these plants and seeds. What is preserved? How do we recover these remains of the past? With assistance this week from a guest blogger Roger Moeller, PhD, we will learn about the floatation process.

The flotation process is very simple. The best flotation tub is a square, galvanized, handled, wash tub (12 gal Dovertm) with the bottom replaced by 1/16” hardware cloth. Standing in flowing water with the tub submerged to within 3" of the rim, slowly pour soil into the tub while agitating the tub in a circular pattern. When the all the fine-grained soil has passed through the screen, skim the floating materials with a tea strainer and place them onto a drying pan. When all the floating material has been skimmed, lift the tub out of the water and pour the heavy portion onto the same or separate drying pan. When the materials have dried, sort them into seeds, bones, lithics, charcoal, and other categories. Each different item is identified and quantified. This sounds very simple, but it is not.

flotation in progress using local water source

Unfortunately all of these good intentions and hard work are more than likely to produce at best inconsistent truisms if the samples are too small, not intensively or systematically collected, or culturally biased. The keys to the flotation trap are that random samples produce random results, small samples produce small results, and culturally biased samples produce meaningless results. Stratigraphy must be followed, and holistic studies are the only way to create a complete data set. Flotation is of undeniable importance in determining the qualitative nature of data present. Without it, data interpretation is severely handicapped or, even worse, misleading.

Excavations at one site prior to the use of flotation recovered only a small quantity of bone. The assumption was made that the acidic soil had long since destroyed all but the large, heavy bones. Flotation showed a variety of small mammals, fish, birds, amphibians, and a much wider distribution of mussels which had only been inferred previously. Even though they may represent only a small fraction of the total bone recovered by weight, the species they represent played a role in aboriginal subsistence and must be taken into account.

sorting float material back at the lab

There is also the smaller debitage (byproducts of stone tool manufacture) which is indicative of close retouch or reworking of artifacts. Missing these data would distort the range of manufacturing and maintenance tasks undertaken. The identification of seed remains provides the necessary data for determining diet, seasonality, eco-niches exploited, reasons for the encampments, and possible techniques for food preparation and preservation. Without flotation very few seeds would ever be recovered during excavation.

The discarded soil matrix as well as control samples from seemingly non-cultural zones should be analyzed as closely as the cultural samples. What seems intuitively obvious in the field when the context was positive should be quantified and described for those contexts of unknown integrity. What is not found can be as important as what is found. The recent contaminants (background noise) can yield data crucial to interpreting the occupation. One's interpretation can be biased by the nature of the flotation sampling regime. To understand what should be done, one must start by defining a meaningful cultural context, proceed with the appropriate equipment, conduct an intensive analysis of all materials found in the dried flotation samples, and interpret everything within a holistic framework.

Everything present means something in relation to everything else. Flotation sampling should be thought of in the same light as soil coring. There must be a precise level by level record of the soil strata which can be examined for color, texture, nature of inclusions, and cultural materials. Many samples are taken since there is no reason to assume that the strata or contexts are identical everywhere on the site. The precise location of the sample is mapped to facilitate its correlation with other observations, artifacts, and ecofacts to aid in the analysis and interpretation of the site.

flotation material sorted and bagged by artifact type

Flotation is by far the most economical and efficient technique yet devised for the large scale recovery of small scale remains from archaeological deposits. At one site all the thousands of carbonized seeds, most of the identifiable bones, and a small percentage of the thousands of artifacts examined, counted, and classified were the result of flotation.

Dr. Moeller has addressed some of the key issues in the floatation process. As he points out paramount to the success of this type of analysis is the need for controlled collection and floatation from every level of a site and across a broad scope. This level of analysis is time consuming and often costly, but the benefits have far outweighed the costs in terms of identifying the food sources of Native peoples. Archaeologists are enhancing this data set every time an excavation is conducted utilizing floatation. We often have written about “painting a picture of our past” this is the type of data that strengthens our analysis and interpretation.

Paleoethnobotanists have identified the presence of squash much earlier in the archaeological record than previously thought. This evidence needs to be tested against other data to ensure its accuracy, but archaeologists are excited by this increased interest in floatation and the merits of research. As we sit down to our Thanksgiving meal, let’s take a moment to reflect on the role of prehistory on the development of the plants, nuts and seeds we enjoy today.

Keep checking back with us over the next few weeks as we continue to develop our Farm Show exhibit on Native American foodways in Pennsylvania, and mark your calendars for the week of January 7th to visit the exhibit at thePennsylvania Farm Show Building.

For more information, visit or the Hall of Anthropology and Archaeology at The State Museum of Pennsylvania .

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