Human evolution was critically influenced by climate fluctuations says study

First Posted: Dec 26, 2012 01:12 PM EST

Human evolution could have been accelerated by rapid environmental changes that happened around 2 million years ago in East Africa, instead of a slow one time change in climate, as previously thought. Researchers at Penn State and Rutgers University found that "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".

Compared to this, the current leading hypothesis suggests that evolutionary changes among humans during the period the team investigated were related to a long, steady environmental change or even one big change in climate, said Katherine Freeman, professor of geosciences, Penn State.

"There is a view this time in Africa was the 'Great Drying,' when the environment slowly dried out over 3 million years," she said. "But our data show that it was not a grand progression towards dry; the environment was highly variable."

The reason that this is important to, and potentially speeding up, evolution is that variability of experience can trigger cognitive development, according to anthropologists. The researchers explain in their release, that the changing vegetation posed a challenge to humans living at that time: "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 new findings about the climate of that period were gained by examining organic matter in sediments from northern Tanzania. Employing gas chromatography and mass spectrometry to determine the relative abundances of different leaf waxes and the abundance of carbon isotopes for different leaf waxes, it was possible to proof the occurence of several different climate periods, with different kind of plant growth.

THe team used mathematical and statistical models to correlate the environmental change in East Africa with other climate factors. "We find complementary forcing mechanisms: one is the way Earth orbits, and the other is variation in ocean temperatures surrounding Africa," said Prof. Freeman. 

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