New charcoal and plant microfossil evidence from Mexicos 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 Smithsonians National Museum of Natural History and the Smithsonian Tropical Research Institute in Panama.
Pipernos 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.