Ancient Seeds Sow Debate Over Sunflower-Farming Origins

Scott Norris
for National Geographic News

April 28, 2008

Editor's note: For further discussion on the origin of sunflower farming, see the Letters section of the journal Proceedings of the National Academy of Sciences.

Sunflowers were grown as a domesticated crop in Mexico more than 2,000 years ago, according to a new study.

The new findings run counter to a theory that sunflower farming began in what is now the U.S. East and then trickled south into Mexico.

Plant remains discovered in a dry cave suggest that farmers in Mexico were cultivating sunflower strains with large seeds by around 300 B.C.

A 2001 study by the same team had found evidence of Mexican sunflower domestication as early as 2600 B.C., but that finding was controversial.

A Smithsonian Institution expert on early agriculture has argued that the remains described by the team in 2001 had been incorrectly identified as sunflowers.

Eastern U.S. Origins

Sunflowers were a cultivated food crop in what is now the eastern United States 4,000 to 5,000 years ago, most experts agree.

But did sunflower farming spread south from eastern North America to Mexico and beyond? Or did ancient Mexicans develop sunflower farming on their own?

The latest evidence supports an independent origin for Mexican sunflower farming, said study leader David Lentz of the University of Cincinnati.

"We have filled in the gaps with lots of additional data that now make the Mexican sunflower [domestication] hypothesis irrefutable," Lentz said.

"Given all available data, the best explanation is that the sunflower was domesticated twice."

The study by Lentz's team was funded in part by the National Geographic Society's Committee for Research and Exploration and will appear in tomorrow's edition of the journal Proceedings of the National Academy of Sciences. (National Geographic News is part of the National Geographic Society.)

(See also "Ancient Chilies Suggest Spicy Cuisine in Early Mexico" [July 10, 2007].)

The new archaeological evidence consists of three large and well-preserved sunflower "achenes"—fruits containing seeds—unearthed at a site called Cueva del Gallo in the Mexican state of Morelos.

"Early farmers selected for large achene size," Lentz said.

"Through time, the achenes become noticeably bigger than those of any wild sunflowers, and at that point we know they were domesticated."

Bruce Smith, the Smithsonian expert who cast doubt on Lentz's earlier study, said the new paper still provides no strong evidence that domestication occurred outside of eastern North America. (Smith is a member of the National Geographic Committee for Research and Exploration.)

"Genetic research shows that all present-day domesticated sunflowers originated from a single domestication event, from wild progenitor populations in the central United States," said Smith, of the Smithsonian's National Museum of Natural History in Washington, D.C.

Smith believes that domestic sunflower strains could easily have spread from the U.S. into Mexico by 300 B.C.

If sunflower cultivation were widespread in ancient Mexico, he added, many more clearly identifiable remains would have been found.

"Even if sunflower was domesticated independently in Mexico, then it was a sidebar event, and the resultant domesticate did not endure up to the present day," Smith said.

Study author Lentz counters that additional, still undescribed Mexican sunflower remains are probably already present in museum collections. For example, the remains described in his team's new paper were first collected in 1996 but not studied until now.

Also, the larger size of Mexican achenes, compared to U.S. specimens, makes a north-to-south transfer unlikely, Lentz said.

The genetic studies that Smith cites as evidence of a north-to-south transfer are inconclusive, Lentz added, because they did not include sunflower samples of known Mexican origin.

Ceremonial Uses

Sunflower fruit may never have been as important a food source in ancient Mexico as in the eastern U.S., Lentz's team says. But the plants may have been used in different ways throughout history.

"There appears to have been a shift over time from food to ceremonial uses" in Mexico, Lentz said.

Lentz's team interviewed indigenous people in different parts of Mexico where sunflowers are grown today.

Eleven of 14 indigenous groups had unique words for "sunflower" bearing no resemblance to the Spanish word for the same species, according to the new study. Spaniards did not arrive in Mexico until the 1500s.

This linguistic evidence—along with distinctive traditions associated with the plant—suggest a long history of indigenous Mexican use and not a more recent cultural borrowing, the researchers argue.

They also suggest that the Spanish may have suppressed indigenous use of the sunflower because of the plant's symbolic associations with the sun god and warfare—hence the lack of modern Mexican remains with lineages that can be traced back to ancient times.