For thousands of years, corn has been a dietary staple of many Indigenous cultures in the Americas. Food and drinks containing the cereal—such as an alcoholic drink called cauim, made by the Tupi people—are typical of the Amazonian diet and are often used in rituals. Some Indigenous Brazilian ethnic groups, such as the Mbyá Guaraní, consider them sacred. It is the most widely produced grain worldwide, mostly used as feed for livestock, in addition to a notable presence in the human diet. This has led archaeologists and geneticists to investigate the origin, dispersion, and domestication processes that corn has undergone since the origin of agriculture in the Americas.
New interpretations published in the journal Science Advances in September described the similarities between archaeological samples of corn and modern varieties cultivated by Indigenous people and traditional Brazilian farmers. The authors claim that corn arrived in the southwest of the Amazon 6,000 years ago, and was only partially domesticated at the time, having its origins in Mexico 9,000 years ago. It then underwent various phases of selection and diversification in regions such as the Central-West, South, and Southeast of the country.
This does not mean that domestication in the Amazon is complete. Corn samples from Minas Gerais dated between 570 and 1,010 years old show characteristics compatible with the first corn planted in the Americas. Currently, there are about 300 varieties of corn in the American continent. Of these, 15 are Brazilian, divided into 19 subvarieties, of which four are native, associated with Indigenous peoples: Entrelaçado, Caingang, Avati Moroti, and Lenha.
Flaviane Costa / USPDomestication in the Americas gave rise to great diversity on the continentFlaviane Costa / USP
The scientists analyzed the morphology and DNA of 282 fragmented ears of corn, two whole ears, and 12 ancient kernels found in the Peruaçu Valley, Minas Gerais, in the 1990s by a team from the Natural History Museum of the Federal University of Minas Gerais (UFMG), led by French archaeologist André Prous. One of the authors of the article, agricultural engineer and geneticist Fábio de Oliveira Freitas, from the Genetic Resources and Biotechnology division of the Brazilian Agricultural Research Corporation (EMBRAPA) in Brasília, is currently responsible for curation of the material. “A large amount of material was found at those archaeological sites, especially given the high potential for degradation due to the country’s tropical conditions. The corn was preserved because it was in caves and buried inside baskets,” says geneticist Flaviane Costa, a postdoctoral researcher at the Luiz de Queiroz College of Agriculture of the University of São Paulo (ESALQ-USP) and lead author of the article. She carried out the analyses as part of research led by geneticists Elizabeth Ann Veasey, her PhD advisor, and Maria Imaculada Zucchi, her current advisor.
All the specimens had what biologists call a floury endosperm, meaning a large part of the kernel’s body, where the nutrients are stored, was opaque. Other more transparent versions are classified as vitreous. The archaeological samples were compared with corn varieties with floury endosperms currently cultivated by Indigenous peoples and traditional Brazilian farmers, as well as with teosinte, a wild plant related to corn that is similar to its ancestral form. The teosinte specimens are stored at the Peabody Museum of Archaeology and Ethnology at Harvard University, USA. Information about modern corn was obtained from collections at USP and the University of the Republic in Uruguay.
The archaeological samples are conical ears with four to 40 kernels in four to 18 rows. This is a similar shape to modern teosinte, the cylindrical ears of which have between two and eight rows, each comprised of between six and 27 kernels. Based on these characteristics, the team determined that corn varieties can be classified as primitive—meaning they appeared early in the domestication process—if they had fewer than eight rows, because no modern variety of the cereal in the lowlands of South America has so few. South American varieties generally have around 12 rows, although some have up to 26. Ninety-five percent of the teosinte samples had fewer than eight rows.
Among the 282 samples from Peruaçu Valley, the geneticists found 14 archaeological specimens with four or six rows, despite the fact that domestication of the cereal began 9,000 years ago in Mexico and 5,000 years ago in the western Amazon. “This is something completely new,” says archaeologist Tiago Hermenegildo, a postdoctoral researcher at the Max Planck Institute of Geoanthropology in Germany, who is also affiliated with USP’s Museum of Archaeology and Ethnology (MAE). Hermenegildo is conducting archaeological research on corn in the Amazon, but did not participate in the study. It is a peculiar finding because in theory, the long process of domestication, marked by an increase in the number of rows of kernels, should have eliminated these characteristics.
The discovery, together with comparative data collected by the researchers, suggests that corn was not yet completely domesticated when it arrived in Brazil. “The article is disruptive because until 2018, it was thought that corn was fully domesticated in Mexico,” says Costa. “There was a huge gap in the data for the lowlands of South America (the regions of the continent below 1,500 meters in altitude).”
A 2018 study that mapped the complete genome of several corn varieties from South America found variations in genes associated with domestication. When the process is complete, certain genetic forms (alleles), like those that increase the number of kernels, for example, are expected to be the only ones in existence—fixed, in genetics terminology. “Now we have archaeological examples of corn found in Brazil with primitive characteristics, which corroborates these previous works,” says the ESALQ researcher.
A consensus is yet to be reached. “What genetic studies show is that at the beginning of the domestication process in Mexico, corn underwent a much more intense gene exchange with wild varieties,” says Hermenegildo. “When it arrives in Brazil, this exchange stopped occurring, although there was still gene flow with other varieties in a process of secondary domestication, and this is reinforced by the new research.”
Fábio de Oliveira Freitas / EMBRAPACave paintings in Peruaçu, Minas Gerais, indicate that corn and buriti were part of the lives of the people who inhabited the regionFábio de Oliveira Freitas / EMBRAPA
Migration across the continent
Costa’s group also sought to trace the migration route corn took across the continent by identifying similarities between existing groups and the specimens compared to archaeological samples of the Entrelaçado, Caingang, Avati Moroti, and Lenha varieties, in addition to results from the same varieties published in other articles. This is how they discovered that local specimens of Entrelaçado corn from western Amazonia were similar to archaeological samples found in the Cerrado and Caatinga biomes.
Avati Moroti corn is found in various regions of Brazil. Specimens of the variety found in the Cerrado were similar to a sample from the Atlantic Forest and others described in the scientific literature. Meanwhile, another subvariety of the same strain was identified further south, in the Pampas region. Local varieties of Caingang and Lenha corn also exist in the Pampas and the Atlantic Forest.
All this information allowed the researchers to propose a route that the cereal appears to have taken across South America. They theorize that corn was brought to Brazil by humans migrating to the western Amazon, from where it was taken to the Caatinga and Cerrado regions in the Central-West and Northeast regions of the country. At the same time, other waves of migration also transported the grain to the Atlantic Forest regions, especially in the Southeast, and to the Pampas in the South of Brazil.
Flaviane Costa / USP Teosinte, like these samples from Harvard University, shares similarities with ancestral corn Flaviane Costa / USP
“The scientific community has known about these native corns since 1958, but no one in archaeology paid them any attention until recent years,” points out Hermenegildo. “Current evidence about the plant was completely ignored during decades of archaeological research in the Amazon; the work is fundamental in this sense.”
By highlighting the resilience of corn’s primitive characteristics, the research can also have an impact on current conservation and management policies. For Costa, the millennia-long presence of exclusively South American varieties reinforces the need for public policies and international agreements on their conservation. An absence of such policies could lead to extinction of local and native varieties. “The study highlights the planting carried out by traditional and Indigenous populations.”
For Hermenegildo, this is important because many types of corn planted by Indigenous peoples became extinct along with those who cultivated them. “It was cultural and genetic erosion, which has occurred since colonial times.”
The story above was published with the title “Custom corn” in issue 344 of October/2024.
Project
Populational genomics and phenotype characterization to explain aspects of the origin, domestication, and dispersal of achiote (Bixa orellana) and maize (Zea mays) in the lowlands of South America (n° 15/26837-0); Grant Mechanism Regular Research Grant; Principal Investigator Elizabeth Ann Veasey (USP); Investment R$192,720.56.
Scientific article
COSTA, M. F. et al. Archaeological findings show the extent of primitive characteristics of maize in South America. Science Advances. Vol. 10. Sept. 4, 2024.
