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Ancient Irrigation in Sonoran Desert Shows Humans’ Longstanding ‘Love-Hate’ Relationship With Environment

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Current debates about climate change notwithstanding, humans have tried to harness their environment since time immemorial, from the invention of fire to irrigation.

“Control of natural resources by human groups is a given,” said Jim Watson, Arizona State Museum’s assistant curator of bioarcheology and an anthropology professor at the University of Arizona, in a recent interview. “People have burned prairies to encourage the growth of grasses and mimimize tree growth in farming areas. Human/environmental interactions have a history as long as the existence of our species on the planet. Hominid ancestors began polluting the environment nearly 700,000 years ago with the control of fire and have never looked back. They’ve been modifying their environment every step of the way.”

Watson looks into the past for clues to the future, reconstructing historical discoveries to understand bygone populations and lessons learned by studying the ways they adapted to their changing environment. He is especially interested in understanding prehistoric human adaptations in desert ecosystems and the role that local resources play. Fieldwork in northern Sonora, Mexico, has revealed what he calls a "love-hate" interaction between early inhabitants and their surroundings.

“Since the end of the Ice Age, the environment has been going through fluctuations—dry periods, wet ones, cold and warm cycles—and human groups have responded in different ways,” he said. “Adaptations to a village life and adoption of community agriculture are examples of using landscape to their advantage.”

According to Watson, while long-term environmental trends encouraged stable adaptions, more rapid climate changes required human groups to adapt quickly. Early farmers in the Sonoran Desert did so by employing technological strategies, such as building canals 3,000 years ago to water steep farming slopes during dry spells. The earliest village settlements in the desert utilized geomorphological characteristics of the local landscape to facilitate their rather sophisticated form of irrigation agriculture.

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Other historical, but more current, canals built by the Hohokam in the Phoenix basin were massive in comparison—six feet deep and 12 feet wide versus the earlier two foot deep, three feet wide. But “it’s not the size, it’s the concept,” Watson said. “The development and spread of agriculture among prehistoric human populations throughout the globe catapulted human cultural evolution far beyond those accomplishments of the previous four million years of biological evolution.”

In other words, the issues being discussed this week in Brazil at the United Nations Conference on Sustainable Development, known as Rio+20, were sparked with the invention of fire. It's just that now, Earth's population has reached a level that has scientists from many quarters predicting that the pressure being put on the environment that sustains us may soon reach a point of no return.

“Humans will always come up with ideas, but whether or not they take hold is another story,” Watson said. “It’s about understanding the need for adaptability, and ingenuity is the key. Historically we’ve seen numerous adaptations among O’odham groups caused by environmental changes, going back to traditional technologies like early canals or farming and harvesting in an arid desert landscape.”

Based on his years of research, Watson believes the human/environmental interaction is unidirectional: The environment continues to deteriorate as global human populations expand, even though at times, “Mother Nature does have her say through major natural disasters that directly affect how humans adapt and continue to live in these areas impacted by climate change.”

The past may play a part in our future as the concept of environmental adaption seen in previous cultures becomes a viable option, if not a mandate, he believes.

“We’re currently in a major drying trend, and the environment is changing significantly, whether as a result of global warming or a long-term general global climatic trend that may perpetuate the human love/hate relationship with our environment,” Watson said. “One the one hand, we love it because it provides for us, but on the other hand, we continue to destroy it, to exploit it so we can survive. Hopefully we will be smart enough to adapt to try and save what we haven’t already destroyed.”