Rapid climate change in East Africa about 2 million years ago may have influenced human evolution according to researchers from Rutgers University and Penn State, including Professor of Geosciences at Penn State, Katherine Freeman and Clayton Magill, graduate student in the same department.
"The landscape early humans were inhabiting transitioned rapidly back and forth between a closed woodland and an open grassland about five to six times during a period of 200,000 years," said Clayton Magill "These changes happened very abruptly, with each transition occurring over hundreds to just a few thousand years."
According to Freeman "There is a view this time in Africa was the 'Great Drying,' when the environment slowly dried out over 3 million years, ....But our data show that it was not a grand progression towards dry; the environment was highly variable."
According to the researchers, many anthropologists believe that changing experience and challengesm can lead to advances in evolution.
Magill stated that "Early humans went from having trees available to having only grasses available in just 10 to 100 generations, and their diets would have had to change in response....Changes in food availability, food type or the way you get food can trigger evolutionary mechanisms to deal with those changes. The result can be increased brain size and cognition, changes in locomotion and even social changes -- how you interact with others in a group. Our data are consistent with these hypotheses. We show that the environment changed dramatically over a short time, and this variability coincides with an important period in our human evolution when the genus Homo was first established and when there was first evidence of tool use."
The researchers examined sediments from lakes in Olduvai Gorge in Tanzania. They looked especially for biomarkers, fossilised molecules from ancient organisms, especially leaf waxes, which are tough and survive well. They found that there was a rapid transition between woodland and open grasslands during that period.
They have published two papers, including one showing that rainfall was greater when there were trees and less when there was grassland, pointing to the importance of water in an arid country like Africa.
"The research points to the importance of water in an arid landscape like Africa," said Magill. "The plants are so intimately tied to the water that if you have water shortages, they usually lead to food insecurity.
"Together, these two papers shine light on human evolution because we now have an adaptive perspective. We understand, at least to a first approximation, what kinds of conditions were prevalent in that area and we show that changes in food and water were linked to major evolutionary changes."
Image shows Olduvai Gorge in Tanzania, where the research took place