Currently, the human fossil record shows a correlation with climate patterns in Africa. About 5,000 to 10,000 years ago, the Earth's axis of tilt shifted (a process called precession), which changed the amount of rain that Africa received.
"It is not true that the Sahara Desert has been a permanent feature for millions of years," said Peter deMenocal, a professor at the Lamont-Doherty Earth Observatory at Columbia University. Africa oscillated between wet and dry every few thousand years, and each shift induced adaptation in the creatures that lived in the region.
About 3.35 million years ago, Ethiopia was forested and Lucy's species thrived with its ape-like features. The climate changed and the habitat switched to woodland, and then to the African savannah. Then, about 2.95 million years ago, it switched back to woodland. Unable to adapt, Lucy's species went extinct around this time after 900,000 years.
About 2 million to 2.5 million years ago, an intense dry period led to the first migration of Homo erectus out of Africa into Southeast Asia, according to scientists.
About 5,000 years ago, with the creation of the Sahara Desert, humans migrated into the Nile Delta, creating an urban settlement, according to deMenocal.
"Civilizations and populations can be very plastic that way," said deMenocal. "Climate change alters ecological landscapes, creates unnatural selection pressures, and promotes genetic selection to fit the pressures."
A more visible effect of climate change on human morphology was the development of large nasal cavities in Neanderthals, the most recent relative of the modern human displayed at the Smithsonian.
"We used to think of environment as a backdrop, but now, with the development of environmental records, we are more in tune to the consequences of environmental dynamism," said deMenocal.
Scientists at the Smithsonian panel called for greater field exploration to create a larger record of our past. Gaps in the fossil record make it difficult to closely relate particular adaptations to climate change. Better climate modeling is also necessary, according to deMenocal.
The recent discovery of Australopithecus sediba, a new species of hominid from about 2 million years ago, in Malapa, South Africa, provides a new link that is yet to be correlated with past climate.
"All human species face questions about adaptation, long-term perspectives versus short-term gains," said Potts at the Smithsonian. "I'm hopeful because we are a species that's emerged from a long history of adaptation."
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500