Starchy residue preserved in ancient stone tools may rewrite the story of crop domestication in the American Southwest, according to new research led by the University of Utah.
The Four Corners Potato (Solanum jamesii) has been an important cultural, nutritional and medicinal food staple across the Colorado Plateau for millennia. Despite its long history and contemporary use, the extent to which Indigenous people domesticated S. jamesii remains unknown. Previous genetic research has shown that the tubers were transported and intentionally cultivated far beyond its natural range—two crucial steps toward proving domestication.
In a new study, researchers analyzed 401 ground stone tools from 14 archaeological sites located within and beyond the potato's natural range. They were searching for microscopic starch granules from S. jamesii in the crevices of early food-processing tools—large slabs (metates) and handheld grinding stones (manos). S. jamesii granules were present on tools at nine of the archaeological sites, four of which showed consistent use of the tuber as early as 10,000 years ago.
These findings, combined with independent lines of evidence from nearly a decade of investigation, strongly support that the initial stages of S. jamesii domestication by Indigenous people occurred across the Four Corners region of the United States.
"By adding new archaeological data and ethnographic interviews, we are building a case for domestication of S. jamesii in the American Southwest," said Lisbeth Louderback , anthropologist at the U and the Natural History Museum of Utah and senior author of the study.
The study is the first to define the anthropogenic range of S. jamesii, a product of extensive trading networks across the Colorado Plateau. Indigenous people carried plants from their natural range to establish new populations along a narrow band in the Four Corners region, especially in present-day Escalante, Bears Ears and Mesa Verde.
"Traits of S. jamesii from the anthropogenic range already show evidence of manipulation, including population-based variations in freezing tolerance, extended tuber dormancy, sprouting resilience, and we suspect there are others that can be identified in the genome," said Bruce Pavlik, plant ecologist at BMP Ecosciences, research affiliate at the museum and co-author of the paper. "The next step in the project is to detect artificial selection—the ultimate evidence for full domestication."
These cultivated plants established a unique cultural element centered around the potato that continues to this day. Nearly all Diné (Navajo) elders interviewed for the study had special knowledge of the tuber, referring to it as "nímasii yázhí," a term of personhood known as the tiny potato relative. Hopi elders used the term "tumna." Remnant gardens with live plants can still be found in those ancient gardens, along with the telltale starch granules pressed into the surfaces of stone tools so long ago.
"The mobility of Indigenous foodways was driven by kinship-based practices across the landscape. Indigenous knowledge holders, especially matrilineal women, held on to these seedlings and stories across generations to sustain ties to ancestral land and foodways," said Cynthia Wilson (Diné), doctoral candidate at University of California, Berkeley and co-author of the study.
S. jamesii is a wild tuber native to the Mogollon Rim, a region spanning southcentral Arizona and into the Mogollon Mountains of New Mexico. Here, S. jamesii plants are common across the landscape. Outside of this natural range, populations tend to be small and usually occur within 300 meters of archaeological features.
Compared with red potatoes, Four Corners spuds have three times the protein, twice the calories and essential minerals and much more dietary fiber. The nutritious snacks were highly valued, easy to travel with and provided a consistent diet. In 2024, DNA analysis of the living plant populations revealed genetic corridors along which people transported and cultivated new populations.
Metates and manos
The current study established consistent use of the transplanted potatoes, a crucial data point needed to claim domestication. Indigenous people prepared potatoes and other crops using manos and metates. The grinding process releases starch granules from plant tissues, which get lodged deep into crevices of the stone. Over the last decade, Louderback has advanced the method for extracting, isolating and identifying the starch granules.
"You can tell which stones are tools by their ground surfaces. It's very worn and smooth where the rock has been polished from repeated use," Louderback said. "They could have been used a few times or a hundred times—we don't know. But tools with higher starch yields may suggest that people processed the potato more frequently."
Her team sampled 401 metates and manos from 14 archaeological sites within and beyond the tuber's natural range. More than half of the tools came from the Natural History Museum of Utah's archaeological collections, with the rest borrowed from various repositories across the country.
The tools with the highest proportion of S. jamesii starch granules came from the Four Corners region of southern Utah (North Creek Shelter), southwest Colorado (Long House, Mesa Verde) and northwest New Mexico (Pueblo Bonito, Chaco Canyon). These sites also have populations of live plants growing nearby.
"The starch granules corroborate our previous assertion that tubers were transported long distances, but it also suggests that the species was used persistently for thousands of years within the region we describe as the 'anthropogenic range,'" said Louderback.
Agricultural legacy on the Colorado Plateau
Academia has long dismissed the notion that Indigenous people of the American Southwest domesticated native plants, arguing instead that local agriculture relied primarily on crops domesticated in Mesoamerica, such as maize, beans or squash. Recent studies have challenged this paradigm by presenting evidence of people cultivating and influencing native plants, including agave, barley and amaranth. Yet these studies often fall short when compared to the robust documentation associated with plants from other regions of the world.
In the last decade, the study's research team has pursued multiple, independent lines of evidence for S. jamesii domestication, including genetic, ecological, archaeological, biogeographical, ethnographic and linguistic data. Indigenous people routinely traded plants across the region, altering local landscapes and leaving ecological legacies that persist to this day. In 2021, the research group found dense concentrations of culturally significant plants surrounding archaeological sites , even when the species was absent from the wider environment. The Four Corners potato was one such species.
The study's interviews revealed that Diné farmers and elders still know, grow and eat S. jamesii tubers, as well as use them for spiritual purposes including in water offerings and seedling ceremonies. There was a striking difference in the way interviewees referred to the potato. Women used the present tense and knew how to process and eat the potato—all mentioned using glésh (special white clay) to reduce its bitterness. The men spoke about the potato in the past tense and had no specific understanding of its preparation. The interviewees talked in detail about how they use other wild plants and domesticated crops. All spoke of contemporary struggles, including access issues, that hinders their ability to continue traditional land-use practices and food systems.
"Engaging the voices of Indigenous farmers and foragers on land-use practices is essential to preserve the Indigenous health of the land and the people by maintaining access to the tiny tubers from traditional, undisturbed populations," Wilson said.
