Washington, DC
March 23, 2009
Source: The
National Academy of Sciences
- Wild grass became maize crop
more than 8,700 years ago
- Probably domesticated in the Mexican tropical forest
The earliest physical evidence for
domesticated maize, what some cultures call corn, dates to at
least 8,700 calendar years ago, and it was probably domesticated
by indigenous peoples in the lowland areas of southwestern
Mexico, not the highland areas.
This new evidence comes from an international team of
researchers, who report the findings in two companion papers in
this week's Proceedings of the
National Academy of Sciences. They place maize domestication
in Mexico about 1,500 years earlier than previously documented
there and 1,200 years earlier than the next earliest dated
evidence for maize in Panama.
"Our primary goal was to document the early history of maize
domestication in the homeland of its wild ancestor," said
Anthony Ranere, Department of Anthropology at Temple University,
Philadelphia, Pennsylvania. He acknowledged the timelines make a
good deal of sense because the wild ancestor of maize is native
to the regions of southwestern Mexico where the team worked, and
these regions had not been previously explored by
archaeologists.
Researchers focused on the Xihuatoxtla Shelter in an area of the
Balsas Valley that is home to a large, wild grass called Balsas
teosinte that molecular biologists recently identified as the
ancestor of maize. The shelter contained early maize and squash
remains as well as ancient stone tools used to grind and mill
the plants.
"We found the remains of maize and squash in many contexts from
the earliest occupation levels," said Dolores Piperno, senior
scientist and curator of archaeobotany and South American
archaeology for the Smithsonian's Museum of Natural History in
Washington, D.C. "This indicates these two crops were being
routinely consumed nearly 9,000 years ago."
Ranere and Piperno discuss both the archaeological context and
botanical evidence for maize and squash domestication in the
papers published in the Proceedings of the National Academy of
Sciences. Ranere is the first author of the archaeological
paper, while Piperno is the first author of the botanical paper.
Both papers result from work by the same five investigators,
including Irene Holst, Smithsonian Tropical Research Institute,
Panama; Jose Iriarte, University of Exeter, U.K.; and Ruth
Dickau, Temple University. The research is partially funded by
the National Science Foundation.
"Finding early human settlements in this part of Mexico is also
very important, as it shows people were becoming well-adapted to
tropical forest settings early on," said Piperno. The findings
suggest domestication of maize in Mexico's lowland areas as
opposed to highland areas as has long been thought.
The search for maize origins in the 1950s through the 1970s
focused on arid or semi-arid regions in the Mexican highlands
where preservation of dried out plant remains was common. Not
surprisingly, the earliest maize remains in the form of maize
cobs and kernels came from highland caves and rock shelters.
But search locations shifted when molecular biologists began to
study where the ancestor of maize, teosinte, grows today and
when researchers began using phytoliths and starch grains to
identify maize and other plant species, both domesticated and
wild, in the 1990s. Starch grains and phytoliths are microscopic
particles that occur in leafs, stems and roots of many plants,
and unlike whole seeds and roots are well-preserved in tropical
forest environments, such as those in lowland areas of Mexico
and Panama.
Even more, phytolith and starch grain evidence allowed
researchers to trace the dispersal of maize as a domesticated
crop from its origin in or around the Balsas Valley to Panama by
7,600 years ago and shortly thereafter to Colombia and Ecuador,
and to Uruguay by 4,600 years ago.
The researchers acknowledge, however, that maize already appears
to have been domesticated in the earliest occupation of the
Xihuatoxtla Shelter. "We did not find evidence for the earliest
stages in the domestication process," said Ranere. "We need to
find more ancient deposits in order to document the beginning of
the process."
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Researchers find the earliest evidence of
domesticated maize |
Philadelphi, Pennsylvania
March 20, 2009
Source: Temple
University
Maize was domesticated
from its wild ancestor more than 8,700 years ago
Maize was
domesticated from its wild ancestor more than 8700
years according to biological evidence uncovered by
researchers in the Mexico's Central Balsas River
Valley. This is the earliest dated evidence -- by
1200 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, reported their
findings in two studies -- "The Cultural and
chronological context of early Holocene maize and
squash domestication in the Central Balsas River
Valley, Mexcio" and "Starch grain and phytolith
evidence for early ninth millennium B.P. maize from
the Central Balsas River Valley, Mexico" -- being
published in the PNAS Early edition, March 24.
According to Ranere, recent studies have 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.
"We went to the area where the closest relative to
maize grows, looked for the earliest maize and found
it," said Ranere. "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."
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 7000
years ago. She also found maize and squash
phytoliths -- rigid microscopic bodies found in many
plants -- in lakeside sediments.
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.
Ranere excavated the site and recovered numerous
grinding tools. Radiocarbon dating showed that the
tools dated back at least 8700 years. Although
grinding tools were found beneath the 8700 year
level, the researchers were not able to obtain a
radiocarbon date for the earliest deposits.
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 7600 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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