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What Can Past Climate Change Reveal about Human Adaptation?

How did historic climate change shape human evolution?



LAWRENCE BERKELEY NATIONAL LIBRARY

Research on climate change today focuses mostly on the future, taking stock of how humans have influenced the planet and using computer models to project unwanted changes like warming temperatures or rising seas and ways we might avoid them.

But a new report suggests that there's value in looking at not just how humans shape the climate, but how the climate shaped human development going back millions of years.

"How we get here is relevant to where we are going as a species," says the analysis released yesterday by the National Academy of Sciences. Written at the behest of the National Science Foundation, it lays out a 10- to 20-year plan for research that would improve understanding of the ancient climate and how that influenced human evolution.

Rick Potts, a Smithsonian Institution paleoanthropologist who helped write the report, said thatuntil about 20 years ago, scientists had a simplistic view of how the environment shaped human history. They believed that a few major events, like the expansion of grasslands in Africa and later ice ages in Europe and Asia, signaled forks in the evolutionary path that led to Homo sapiens.

But with more data available now on ancient climate -- such as temperature records derived from sediment cores drilled from lake beds and ocean floors -- researchers now believe humans evolved amid "a great deal of instability and environmental fluctuation," said Potts, director of the Human Origins Program and curator of anthropology at the National Museum of Natural History.

"The human species today is a survivor of lots of different environmental changes," he said. "The possible implication is that we have, built into us, a certain degree of adaptability or resilience."

But history also shows there are limits.

"Look back to the fossil known as 'Lucy' -- her species, Australopithecus afarensis, lived back beyond 3 million years ago," Potts said. "Her species had a certain resilience to environmental change, but her species is no longer around."

A more recent example is the Classic Mayan civilization in southern Mexico and Central America, the report notes. Over a 400-year span between 750 and 1150, the Mayan population dropped by 70 percent or more.

'We're in an experiment that's never been tried'



Some archaeologists believe that a series of protracted droughts helped bring about the Mayans' downfall, basing their controversial theory on climate information gleaned from sediment cores.

Potts said he believes the research program outlined in the new report would help society look to its future, not just better understand its past.

The science academy panel is recommending an effort to broaden the collection of fossils to new geographic areas and across time periods, expand scientific drilling programs in lakes and oceans near sites where ancient humans evolved, and improve climate models to help scientists reconstruct the environment of the past.

That could help researchers understand how fast the environment changed at different points in human history -- and how that compares to conditions today.

"I think we need to look very closely at climate changes in the past and compare them to climate changes in the present and see where our sources of resilience will come from," Potts said. "What we're in now is an experiment that has never been tried. Homo erectus was never able to modify the landscape in the ways we do today."

"There's kind of a cautionary message there," he said, "but also a hopeful one."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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