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Corn Domesticated From Mexican Wild Grass 8,700 Years Ago

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Maize was domesticated from its wild grass ancestor more than 8,700 years ago, according to biological evidence uncovered by researchers in Mexico’s Central Balsas River Valley.

This is the earliest dated evidence — by 1,200 years — for the presence and use of domesticated maize.

The researchers, led by Anthony Ranere of Temple University and Dolores Piperno of the Smithsonian National Museum of Natural History, report their findings in the March 24 edition of Proceedings of the National Academy of Sciences (PNAS).

 

Balsas teosinte, a large wild grass that grows in the Central Balsas River Valley of Mexico, is the closest relative to maize.

Photo courtesy Anthony Ranere/Temple University  

Ranere said that the studies confirmed that maize derived from teosinte, a large wild grass that has five species growing in Mexico, Guatemala and Nicaragua, The teosinte species that is closest to maize is Balsas teosinte, which is native to Mexico’s Central Balsas River Valley, he said in a news statement about the research.

“We went to the area where the closest relative to maize grows, looked for the earliest maize and found it,” Ranere said. “That wasn’t surprising since molecular biologists had determined that Balsas teosinte was the ancestral species to maize. So it made sense that this was where we would find the earliest domestication of maize.”

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The suppression of branching from the stalk of Teosinte resulted in a lower number of ears per plant but allows each ear to grow larger, the National Science Foundation said in a news release about the research. “The hard case around the kernel disappeared over time. Today, maize has just a few ears of corn growing on one unbranched stalk.”

Photo by Nicolle Rager Fuller, National Science Foundation

The study began with Piperno, a Temple University anthropology alumna, finding evidence in the form of pollen and charcoal in lake sediments that forests were being cut down and burned in the Central Balsas River Valley to create agricultural plots by 7,000 years ago, the news statement added.

NGS-Grant-logo.jpg“She also found maize and squash phytoliths — rigid microscopic bodies found in many plants — in lakeside sediments.”

Piperno’s explorations of the origins of maize in the Rio Balsas watershed were funded in part by the National Geographic Society’s Committee for Research and Exploration.

Ranere, an archaeologist, joined in the study to find rock shelters or caves where people lived in that region thousands of years ago.

“His team carried out excavations in four of the 15 caves and rock shelters visited in the region, but only one of them yielded evidence for the early domestication of maize and squash,” the release said.

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Researchers focused on excavating the Xihuatoxtla Shelter in an area of the Balsas Valley in southwestern Mexico. Searching this lowland site represented a shift from previous searches in the Mexican highlands, according to a National Science Foundation news release. “The Xihuatoxtla archaeological site yielded evidence of maize and squash dating back 8,700 years, representing the earliest remains of maize yet discovered.”

Photo courtesy Anthony J. Ranere, Anthropology Department, Temple University

 

Grinding Tools Date Back 8,700 Years

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This 8,700 year-old milling stone was used to process maize and other crops. Maize starch grains were recovered from the cracks and crevasses in the slightly concave surface of the tool, according to a news statement.

Photo courtesy Anthony J. Ranere, Anthropology Department, Temple University

Ranere excavated the site and recovered numerous grinding tools. Radiocarbon dating showed that the tools dated back at least 8,700 years. Although grinding tools were found beneath the 8,700-year level, the researchers were not able to obtain a radiocarbon date for the earliest deposits.

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Previously, the earliest evidence for the cultivation of maize came from Ranere and Piperno’s earlier research in Panama where maize starch and phytoliths dated back 7,600 years.

Ranere said that maize starch, which is different from teosinte starch, was found in crevices of many of the tools that were unearthed.

“We found maize starch in almost every tool that we analyzed, all the way down to the bottom of our site excavations,” Ranere said. “We also found phytoliths that comes from maize or corn cobs, and since teosinte doesn’t have cobs, we knew we had something that had changed from its wild form.”

Ranere said that their findings also supported the premise that maize was domesticated in a lowland seasonal forest context, as opposed to being domesticated in the arid highlands as many researchers had once believed.

“For a long time, I though it strange that researchers argued about the location and age of maize domestication yet never looked in the Central Balsas River Valley, the homeland for the wild ancestor,” said Ranere. “Dolores was the first one to do it.’

In addition to Ranere and Piperno, other researchers in the study included Irene Holst of the Smithsonian Tropical Research Institute, Ruth Dickau of Temple, and Jose Iriarte of the University of Exeter.

The study was funded by the National Science Foundation, National Geographic Society, Wenner-Gren Foundation, Smithsonian National Museum of Natural History, Smithsonian Tropical Research Institute and the Temple University College of Liberal Arts.

 

 

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NGS illustration of Indians farming corn by Roy Anderson

 

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New World Farming Began Around Same Time As Near East’s

Ancient Fig Find May Push Back Birth of Agriculture