Linda Perry spends her days at the Smithsonian National Museum of Natural History in Washington DC, gazing down a microscope at corn kernels and other grains. The grains —often thousands of years old — reveal information about both the farming and trading patterns of long-gone civilizations.

Perry began studying the role that plant foods had played in South American history while doing her doctoral work in the Orinoco valley of Venezuela. The work involved refining techniques for analysing the residues of starch grains on tools used to cut and scrape plant foods. In a study that appears on page 76 of this issue, Perry applied these techniques to identify the remains of ground-up corn in soil and tools collected from a 4,000-year-old house buried in the Andean mountains of Peru. This suggests that the Andean people were grinding the corn to make flour. Perry also found remnants of arrowroot, used today as a thickening agent. This plant does not grow at the altitude where the house was located, but would have flourished in the low-lying rainforest regions. “It provides an important link between the Andes and the tropical rainforests,” says Perry.

Starch grains and silica phytoliths (microscopic chunks of mineral that form inside living plant tissues) are microfossils that are used to identify ancient plant remains. They are particularly useful in tropical climates, where macrofossils such as wood and carbonized charcoal are rarely well preserved. Archeologist Daniel Sandweiss of the University of Maine in Orono recruited Perry and her Smithsonian colleague Dolores Piperno to the Andean project due to their expertise with these residues. Sandweiss was following the trail of deposits of a volcanic rock called obsidian in Peru, near the modern-day town of Alca, in search of evidence that ancient peoples mined and used obsidian. He stumbled on the 4,000-year-old house during a test excavation. While he looked for obsidian and other artefacts, he sent specimens to Washington, where Perry and Piperno carried out starch and phytolith analyses, respectively.

Finding that goods and people moved between the Andes and the rainforest is not a surprise. A famous carving, the Tello obelisk, recovered from the archeological site of Chavín de Huántar, also in the Peruvian Andes, shows carvings of tropical forest plants. “The iconography tells us of a connection between these two areas, but until now there was no solid evidence,” says Perry. She would like to continue to chart this connection by “following the arrowroot track down the mountain”, she says.

Perry, who majored in biology at Tulane University in New Orleans, says that archaeobotany is perfect for her. “It is a combination of things that I love and that challenge me,” she says. “Trying to put together the fossil record is like assembling a very difficult puzzle.”