[Aztlan] EARLIEST CORN DOMESTICATION IN MEXICO

[michael ruggeri]

Source:
Smithsonian Tropical Research Institute
Date:
June 1, 2007

Climate Change Linked To Origins Of Agriculture In Mexico
Science Daily — New charcoal and plant microfossil evidence from  
Mexico's Central Balsas valley links a pivotal cultural shift, crop  
domestication in the New World, to local and regional environmental  
history. Agriculture in the Balsas valley originated and diversified  
during the warm, wet, postglacial period following the much cooler  
and drier climate in the final phases of the last ice age. A  
significant dry period appears to have occurred at the same time as  
the major dry episode associated with the collapse of Mayan  
civilization, Smithsonian researchers and colleagues report in the  
Proceedings of the National Academy of Sciences online.

"Our climate and vegetation studies reveal the ecological settings in  
which people domesticated plants in southwestern Mexico. They also  
emphasize the long-term effects of agriculture on the environment,"  
said Dolores Piperno, curator of archaeobotany and South American  
archaeology at the Smithsonian's National Museum of Natural History  
and the Smithsonian Tropical Research Institute in Panama.
Piperno's co-authors include Enrique Moreno and Irene Holst, research  
assistants at STRI; Jose Iriarte, lecturer in archaeology at the  
University of Exeter in England; Matthew Lachinet, assistant  
professor at the University of Nevada in Las Vegas; John Jones,  
assistant professor at Washington State University; Anthony Ranere,  
professor at Temple University; and Ron Castanzo, research  
collaborator at the National Museum of Natural History.
Pollen of Podocarpus, a conifer now found primarily at higher  
elevations, is common in the oldest strata of sediment cores taken  
from lakes and a swamp in the central Balsas watershed. Along with  
pollen from grasses and other dryland plants, the Podocarpus  
indicates the environment encountered by humans at the end of the  
last ice age (14,000-10,000 B.P.) was drier and 4 or 5 degrees  
Centigrade cooler than it is today.
The Balsas valley is one of the most likely sites for the  
domestication of corn (Zea mays) from its wild ancestor, teosinte  
(Zea mays ssp. parviglumis) because populations of modern teosinte  
from that region are genetically closest to maize. As the lakes  
formed beginning around 10,000 B.P., they became magnets for human  
populations who exploited the fertile soils and rich aquatic  
resources the lakes contained. The researchers found prehistoric  
pottery sherds and other artifacts in sediments at the edges of the  
lakes. At one lake, phytolith data shows that maize and squash were  
probably planted at the fertile edges by 8000 B.P. Pollen from  
teosinte is indistinguishable from that of maize, but Zea pollen is  
consistently present in the cores since the end of the last ice age.
Pollen and phytoliths from weeds associated with crop plants become  
plentiful in the cores at roughly 6300 B.P Charcoal associated with  
agricultural burning practices also is abundant at that time. Between  
1800 B.P. and 900 B.P., a major drying event occurred, corresponding  
to the time when a drought occurred in the region of the Classic  
Mayan civilization. This evidence shows that even during the  
Holocene, severe, short-term climatic oscillations occurred that may  
have had considerable importance for social change.
"We continue to find that tropical forests played a much more  
important role in the origin of agriculture in the New World than was  
once thought," Piperno said.
The team will publish evidence from corresponding archaeological  
excavations of nearby caves and rock shelters that will begin to fill  
in cultural information that accompanied these changes and date them  
more precisely.
Note: This story has been adapted from a news release issued by  
Smithsonian Tropical Research Institute.


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