Starch residue in ancient tool proves potato use in Utah goes back 10,000+ years

The town of Escalante in southern Utah is no small potatoes when it comes to scientific discovery; a new archaeological finding within its borders may rewrite the story of tuber domestication.

Researchers from the Natural History Museum of Utah and Red Butte Garden at the University of Utah have discovered potato starch residues in the crevices of a 10,900-year-old stone tool in Escalante, Utah — the earliest evidence of wild potato use in North America.

This is the first archaeological study to identify a spud-bearing species native to the southwestern United States, Solanum jamesii, as an important part of ancient human diets. The researchers pieced together evidence from stone tools, ethnographic literature and modern gardeners to show that Utahans have used the species intermittently for over 10,000 years. The Escalante area was even previously known as “Potato Valley” to early settlers.

Several Native American tribes, including Apache, Hopi, Kawaik, Navajo, Southern Paiute, Tewa, Zia and Zuni, consumed S. jamesii. The groups used various cooking and processing techniques, including boiling the potatoes, grinding them into flour or yeast, and mixing the potatoes with clay to reduce bitterness. Some groups still tend their potato populations in cultivated gardens.

The long history could mean that the species was transported, cultivated or even domesticated. If true, S. jamesii would be the first example of a plant domesticated in the western U.S. To find out, the researchers are collaborating with geneticists from the United States Department of Agriculture, who are mining S. jamesii’s DNA for genes resistant to drought and disease that could help diversify current potato crops to be more resilient.

Archaeologists use mathematical models derived from foraging theory to describe how and why people foraged for food resources. Using what is called the diet breadth model, archaeologists rank dietary animals and plants according to their energy content and the effort required to harvest and process the food.

The discovery of S. jamesii consumption adds a new energy source that has been largely ignored in ancient diets, partly because tubers don’t preserve well in archaeological deposits. Unlike animal bones and corn cobs, tubers are composed of soft tissues that disintegrate easily. Yet they pack a caloric punch, and are important for understanding ancient peoples’ way of life.

Louderback examined large sandstone slabs called metates and handheld grinding stones called manos, the ancient food processors on which people prepared meals. She found microscopic starch granules that previous archaeologists never suspected were present.

Lisbeth Louderback:

“Grinding plant tissues with manos and metates releases granules that get lodged in the tiny cracks of stone, preserving them for thousands of years. Archaeologists can retrieve them using chemicals, modern microscopy and advanced imaging techniques.”

The researchers want to make the potatoes available for the Escalante community to grow in their gardens to help with conservation. But first, they need to untangle the mysterious ecology of the potato in the wild — its pollinators and conditions necessary for sexual reproduction are still unknown.

Bruce Pavlik:

“We are working with the people of Escalante to bring awareness to this valuable resource and show them what the species looks like, where it grows, its tremendous history and enlist their help as stewards of the Four Corners potato.”

This work was funded by the National Science Foundation and the Vice President for Research Funding Incentive Seed Grant Program at University of Utah.