Piperno, from the Smithsonian Tropical Research Institute and the Archaebiology Program at the National Museum of Natural History, and her STRI colleague Irene Holst had used starch analysis to chronicle plant domestication in the New World tropics.

Harvard University archaeologist Ehud Weiss and Dani Nadel, at the University of Haifa, had excavated a well-known paleo site in Israel, Ohalo II, and carried out analysis of the numerous macroscopic remains of seeds and fruits found there. When Piperno and Weiss met for the first time a few years ago at a conference luncheon, they discussed the possibilities of applying starch grain analysis to artifacts from this Old World site.

Starch grain analysis is painstaking work. First, a fine needle is used to dislodge minute particles from the face of a grinding stone. Then, the entire stone is placed in a sonicator, a water bath in which sound waves vibrate the artifact until smaller particles float free. Each microscopic starch grain is compared to starch grains from hundreds of species maintained in a modern reference collection of plants. “We had used starch grain analysis to study the development of agriculture in the tropics, where plant materials are poorly preserved,” explained Piperno. Significant and consistent differences in shape, size, and other features make it possible to distinguish starch grains from different plant species.

Grinding stones like the one found at Ohalo II have been excavated from other Old World sites dated to 13,000 – 45,000 years before present, but there has never been conclusive evidence to show that they were used to grind cereal grains or other types of plants, and not pigments. “It will be exciting to continue to analyze some of these older artifacts, to see if we can find evidence that they were used to process plants. We’re trying to find answers to two big questions: When were the first wild grains systematically collected as food and when did people begin to process seeds and underground plant organs to turn them into more digestible and nutritious dietary elements.”